No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Relation between microbiological quality, metabolite production and sensory quality of equilibrium modified atmosphere packaged fresh-cut produce
Abstract
The quality of four types of fresh-cut produce, packaged in consumer-sized packages under an equilibrium modified atmosphere and stored at 7 degrees C, was assessed by establishing the relation between the microbial outgrowth and the corresponding production of nonvolatile compounds and related sensory disorders. In vitro experiments, performed on a lettuce-juice-agar, demonstrated the production of nonvolatile compounds by spoilage causing lactic acid bacteria and Enterobacteriaceae. Pseudomonas fluorescens and yeasts, however, were not able to produce detectable amounts of nonvolatile metabolites. The type of spoilage and quality deterioration in vivo depended on the type of vegetable. Mixed lettuce and chicory endives, leafy tissues, containing naturally low concentrations of sugars, showed a spoilage dominated by Gram-negative microorganisms, which are not producing nonvolatile compounds. Sensory problems were associated with visual properties and the metabolic activity of the plant tissue. Mixed bell peppers and grated celeriac, on the other hand, demonstrated a fast and intense growth of spoilage microorganisms, dominated by lactic acid bacteria and yeasts. This proliferation resulted in detectable levels of organic acids and the rejection by the trained sensory panel was based on the negative perception of the organoleptical properties (off-flavour, odour and taste). The applied microbiological criteria corresponded well with detectable changes in sensory properties and measurable concentrations of nonvolatile compounds, surely in the cases where lactic acid bacteria and yeasts were provoking spoilage. Consequently, the freshness of minimally processed vegetables, sensitive for outgrowth of lactic acid bacteria and yeasts (e.g., carrots, celeriac, bell peppers, mixtures with non-leafy vegetables) can be evaluated via analysis of the produced nonvolatile compounds.
... The unavoidable spoilage of vegetables with time is characterized by brown discoloration, necrosis, loss of texture, exudation and/or production of off-flavors (Ponce et al., 2002). Most studies linked sensory rejection of RTE vegetables point to an increased microbial load (Jacxsens et al., 2003;Ragaert et al., 2006). ...
... In the same direction, LAB are described as microorganisms with high spoilage capacity in these products (Pothakos et al., 2014). Within this group, Leuconostoc or Lactobacillus had been identified as some of the main causes of deterioration in salads (Nguyen-the & Carlin, 1994;Pothakos et al., 2014), but the levels reported hereby are below the, in theory, acceptable initial level (10 4 cfu.g -1 ) (Jacxsens et al., 2003). Flavobacterium, the mayor genus, is described as no-SSO in fish (Parlapani et al., 2013), but some strains can produce aromas related with chicken spoilage (Freeman et al., 1976) and it has been proposed as spoilage bacteria in frozen vegetables (Manani et al., 2006). ...
Spoilage flora is critical in vegetal ready to eat (RTE) product shelf-life and selecting efficient spoilage control technologies depends on the microorganisms present. This manuscript describes the evolution of the bacteriome of Batavia RTE lettuce, from fresh lettuce up to completely spoiled (day 14) and correlate these results with the sensorial characteristics. Research Method: The microbiome of vegetal RTE were examined using culture-dependent and culture-independent (16S rRNA metabarcoding) methods. Culture-dependent methods were related with the metagenomic results and sensory analysis to describe the evolution during spoilage and shelf-life. Findings: Our results demonstrated that the RTE lettuce bacteriome during spoilage is dominated by Gram-negative bacteria, mainly Flavobacterium and Pseudomonas. A bacterial population of 22 operational taxonomic units (OTUs) represent up to 96% of total bacterial reads and is maintained during the spoilage, representing the bacterial core of RTE lettuce. A high correlation was detected between culture-independent and culture-dependent results, both in general and selective culture media. Sensorial analysis of lettuce demonstrated that "odor" was the key parameter to determine the sensorial spoilage time and is related to total microbial load and to high concentrations of spoilage-related bacterial genera. Limitations: Hereby presented results are limited by the lettuce variety and by the storage conditions (MAP, 6°C, up to 14 days). Originality/Value: This paper describes an overview of the microbial and sensory evolution during spoilage of Batavia lettuce under MAP. A combination of culture-dependent and independent methods and sensorial analysis were used up to 14 days of storag
... The PCA profile of day 4 almost overlapped with day 0, while those of day 8 and day 12 were clearly separated from day 0-4, indicating that the flavor quality deteriorated significantly after 8 days of storage and that the e-nose could be used to discriminate the freshness of peeled potatoes. Furthermore, the off-odor may be caused by spoilage bacteria (Enterobacteriaceae, Erwinia, Leuconostoc and Lactococcus) due to fermenting sugar [24,28,44]. A principal component analysis (PCA) was used to analyze the differences of the flavor profiles of samples from different storage periods (Figure 5b). ...
... The PCA profile of day 4 almost overlapped with day 0, while those of day 8 and day 12 were clearly separated from day 0-4, indicating that the flavor quality deteriorated significantly after 8 days of storage and that the e-nose could be used to discriminate the freshness of peeled potatoes. Furthermore, the off-odor may be caused by spoilage bacteria (Enterobacteriaceae, Erwinia, Leuconostoc and Lactococcus) due to fermenting sugar [24,28,44]. ...
To reveal the potential relationship between the bacterial community and quality attributes of vacuum-packaged peeled potatoes, the bacterial community dynamics, visual quality, organic acids, flavor and volatile organic compounds (VOCs) during 12 days of storage under 10 °C were studied, and a correlation analysis was performed between the bacterial community and VOCs. During the whole storage, the dominant bacteria changed from Ralstonia, Pseudomonas, Pantoea and Comamonas to Clostridia, Clostridium, Lacrimispora, Lactococcus and Leuconostoc. The visual quality and hardness deteriorated significantly on day 12; meanwhile, lactic and acetic acid content accumulated to 0.79 and 4.87 mg/g FW, respectively. Potatoes’ flavor deteriorated severely after 8 days, as evidenced by results of an electronic nose (e-nose). A total of 37 VOCs were detected, and the total content showed an increasing trend from 2164.85 to 10658.68 μg/kg during the whole storage. A correlation analysis showed that Enterobacteriaceae, Erwinia, Lacrimispora, Lactococcus, Serratia, Pantoea, Clostridium, Flavobacterium and Clostridia were positively correlated with the biosynthesis of VOCs. In addition, 10 spoilage markers were screened according to a variable importance in projection (VIP) ≥ 1. Ethanol, which was the most abundant spoilage marker, was significantly related to Enterobacteriaceae, Erwinia, Lacrimispora and Lactococcus. The results of this study have great practical significance for prolonging the shelf life of fresh-cut agricultural produce.
... During anaerobic fermentation, water-soluble carbohydrates (WSC) are metabolically decomposed into lactic acid by lactic acid bacteria (LAB) until the pH drops to about 4.5 [12]. Additives can further improve the quality of silage [13]. Common additive types include fermentation accelerators and fermentation inhibitors. ...
... After the addition of cellulase, the dominant genus shifted from Lactococcus at 30 days to Lactobacillus at 60 days [26]. Jacxsens et al. [13] revealed that Pantoea agglomerans would be metabolized to produce acetic acid, propionic acid, and succinic acid. Enterobacteriaceae is also capable of producing sugar metabolism under anaerobic conditions. ...
Background: The objective of this study was to evaluate the chemical compositions and microbial communities of salt-tolerant alfalfa silage. Salt-tolerant alfalfa was ensiled with no additive control, and cellulase for 30 and 60 to 90 days. In this study, the dry matter (DM) content of the raw material was 29.9% DM, and the crude protein (CP) content of the alfalfa was 21.9% CP.
Results: After 30 days of fermentation, the DM content with the cellulase treatment was reduced by 3.6%, and the CP content was reduced by 12.7%. After 60 days of fermentation, compared with alfalfa raw material, the DM content in the control group (CK) was reduced by 1%, the CP content was reduced by 9.5%, and the WSC (water-soluble carbohydrates) content was reduced by 22.6%. With the cellulase, the lactic acid content of the 30- and 60-day silages was 2.66% DM and 3.48% DM. The content of Firmicutes in salinized alfalfa raw material was less than 0.1% of the total bacterial content. Before and after ensiling, the microbes had similar composition at the phylum level, and were composed of Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria. The abundance of Pantoea was dominant in fresh alfalfa. In the absence of additives, after 30 days and 60 days of silage, the dominant lactic acid bacteria species became Lactococcus and Enterococcus.
Conclusions: The results showed that LAB (Lactobacillus, Lactococcus, Enterococcus, and Pediococcus) played a major role in the fermentation of saline alfalfa silage. It also can better preserve the nutrients of saline alfalfa silage. The fermentation time would also change the microbial community of silage fermentation.
... Yeast and molds slightly increased during 14 days storage at 4 • C, except for SAR in the July harvest where the increase was significant (Table 5). However, values were between 2 and 3 Log 10 CFU·g −1 , which are much lower than the critical limit for yeasts and molds (5 Log 10 CFU·g −1 ) [34]. In the July harvest there was an increase in bacterial counts after 14 days storage at 4 • C for SAL and SAR (Table 5). ...
... In the July harvest there was an increase in bacterial counts after 14 days storage at 4 • C for SAL and SAR (Table 5). However, the bacterial counts, 4 Log 10 CFU·g −1 , were still much lower than the critical limits of 8 Log 10 CFU·g −1 [34]. ...
The aim of this work was to study the potential of two halophytes for fresh salads. Sarcocornia perennis (SAR) and Salicornia ramosissima (SAL) plant tips were harvested in May and July, and stored at 4 °C for 14 days. At harvest, mineral analyses (Na, K, Mg, Ca, P, N, Fe, Zn, Cu, Pb and Cd), chlorophyll content, protein, β-carotene and ascorbic acid were performed. Color (CIELab), phenolics, antioxidant activity and microbial contamination were measured at harvest and after 14 days storage at 4 °C, and a taste panel evaluated the products. SAL had generally slightly higher values of vitamin C, phenols and carotenoids than SAR. In SAR after 14 days of storage, the levels of phenols and the antioxidant activity were higher than at harvest, both in May and July. The opposite was observed for SAL. In this case, only the antioxidant activity was higher after 14 days of storage. Microbial contamination was very low, not reaching even half of critical limits. Both halophytes had good nutritional value, being suitable for use as fresh salads which can be stored for up to 14 days at 4 °C. SAR seems to be a better source of antioxidants, Ca and Fe than SAL and has less general quality and nutritional value changes from harvest time through cold storage. Fresh tips of both halophytes showed better appearance and nutritional quality when harvested in the early season (May) than at the end of the season (July).
... The TB and Y+M counts were performed on d0 and on d9, after incubation at 30 °C for 48 h. The results were expressed as colony-forming units (cfu g -1 ) FW (Abadias et al. 2008, ISO 21527-1:2008, ISO 4833:2003, Jacxsens et al. 2003). ...
... g -1 FW suggested by various authors for fresh-cut vegetables as the maximum recommended limit for consumption, although exceeding the microbial limit does not always result in the occurrence of visual defects (Scuderi et al. 2011). A higher amount of TB than of Y+M can be expected in fresh and minimally processed vegetables (Jacxsens et al. 2003). ...
The objective of this study was to evaluate the impact of different mixtures of two fresh-cut baby lettuce (Lactuca sativa L. var. crispa cv. Lollo Bionda [LB] and cv. Lollo Rossa [LR]) cultivars on lettuce phytochemical composition during postharvest. Lettuces were grown in a soilless culture system with continuous flotation (FL) in a greenhouse, mixed at harvest and packaged in polypropylene bags and stored at 4 °C for 9 days (d9). Mixes were made of 100, 75, 50, 25 and 0% of LB, respectively. The results showed that the phytochemicals were preserved during storage. In specific, 25LB had the highest pigment content on d1, while 50LB and 25LB had the highest inherent quality on d1.FL led to a reduced microbial contamination, thus, limiting its growth during storage. The results have revealed that high quality and microbiologically safe baby leaf vegetables (BLV), can be obtained by means of FL. The adopting a mix of lettuce cultivars could represent a positive postharvest practice to preserve the phytochemicals of BLV throughout their shelf life.
... An increase was observed in the acidity levels of both washed and unwashed samples (Table 1). Acid formation as a result of carbohydrate breakdown due to microbial growth [21] and chemical reactions might be the reason for the increase in acidity. Washing process and gases used in modified atmosphere packaging were found to have insignificant effect on acidity during storage (P>0.05). ...
... More taste loss was generally observed in the washed and vacuum packaged olive samples (Figure 2b). Low O2 levels in the packages were reported to contribute to an undesired taste formation [21,28]. The level of taste loss was higher for the washed samples when compared to the unwashed ones, however the effect of washing process on taste loss was found insignificant (P>0.05). ...
Hurma olive is a special olive cultivar that loses its bitter taste before harvesting, and sweetness occurs when the fruit is still on the tree. Thus, it can be directly consumed right after being harvested. Studies on the preservation of Hurma olive without salt have been very limited and it has not been implemented in practice yet. In this study, some quality characteristics of Hurma olives under different modified atmospheres were determined during storage. For this purpose, the efficacy of washing, lactic acid dip, and modified atmosphere packaging (MAP) were studied throughout 120 days at 1°C. Hurma olive samples were washed with tap water and dipped in lactic acid solution (0.2% w/v) for 1 minute before packaging. After the application of vacuum, samples were packaged under the atmosphere of 100% CO2, 60% CO2 / 40% N2, and air combination and then stored at 1°C for 120 days. Physicochemical analyses such as acidity, reduced sugar, bitterness, color (CIE L*, a*, b*) and dry matter contents along with sensory analyses were carried out at regular intervals throughout the storage period. Insignificant differences were determined among washed and unwashed Hurma olives in terms of their physicochemical parameters whereas unwashed olive samples retained sensory characteristics better and preferred more by sensory panelists than washed counterparts. Washed and vacuum packaged samples had more undesired values in terms of the sensory characteristics studied.
... mall fresh fruits, such as straw berries, raspberries, currants and grapes and delicate varieties of apples (Sivertsvik et al., 2002) [29] . Ethylene in the atmosphere is used to accelerate ripening or produce a desired color change and it is not considered preservative, although a combination of this gas and activated hydrocarbons can be utilized (Jacxsens et al,. 2003) [15] . ...
... Ethylene in the atmosphere is used to accelerate ripening or produce a desired color change and it is not considered preservative, although a combination of this gas and activated hydrocarbons can be utilized (Jacxsens et al,. 2003) [15] . ...
Consumption of vegetable and fruit commodities has intensely augmented about 30% in each part of the world throughout past decades, but its wastage was also assessed around 20 % of all vegetables and fruits produced each year. Simultaneously, customer need for accessibility commodity is growing and so is the demand for fresh-cut vegetables and fruit. Yet the standard and safety of such commodity is the subject of matter as they are more vulnerable to deterioration and can enable quick development of putrefactive microorganisms. Spoilage may rise from insect damage, indigenous enzyme activity and physical damage in the plant tissue or by microbial contaminations. The emphasis of this discussion is to deliver a general overview of the damages and distinctive microbial spoilage of vegetable and fruits and also some of the innovative techniques to avert the deterioration and prolong the shelf life.
... Wash water of poor sanitary quality and contaminated with enteric pathogens is another potential source of microbial contamination of RTE crops Holvoet et al., 2012). Maintaining clean and hygienic conditions during the packaging of RTEFP after drying, coupled with clean packaging material, can greatly help in combating cross-contamination of the produce and extending their shelf life (FAO, 2010;Jacxsens et al., 2003). ...
In the last decade, there has been a significant move toward healthy lifestyle habits and dietary choices, accelerating the global demand, market trade, and consumption of Ready-To-Eat Fresh Produce (RTEFP), including leafy green vegetables, salads, and fruits. However, consumption of such food items may result in human exposure to foodborne pathogens due to minimal processing and the lack of microbial inactivation steps during their preparation. This review summarises the key enteric pathogens potentially contaminating RTEFP, discusses safety risk factors, sources, and transmission, and summarises existing quantitative microbial risk assessment approaches used to model pathogenic loads. A strategic literature search across different scientific databases collated and presented the current state of knowledge for the present review. The research found that on the one hand, several possible contamination routes such as soil, irrigation water, and manure can introduce human pathogenic microorganisms in the pre-harvest stage; on the other, the temperature, storage, packaging, and sanitation processes of the fresh produce chain may affect the growth kinetics of microbes during the post-harvest stage. Many uncertainties and variabilities are likely to be present in microbial growth/ decay/ post-harvest storage/ inactivation data. In addition, the creation of full-spectra dose-response models of pathogens based on transmission routes, response type, and appropriate host species requires future research. Therefore, applying probabilistic/ stochastic quantitative microbial risk assessment models, including the Monte Carlo simulation approach, can benefit the identification and quantification of potential microbiological hazards across the farm-to-fork chain in RTEFP.
... 5 Temperature is a fundamental parameter affecting microbial growth along with the volatile aroma of the fruit. [6][7][8] Previous studies carried out on fresh-cut fruits, such as strawberries, melon and cantaloupes, have revealed changes in the aroma profile during storage. [9][10][11] Researchers have demonstrated enhanced aldehyde to its corresponding alcohol ratio for tomatoes stored under refrigerated conditions (10 and 20°C). ...
Headspace solid‐phase microextraction and gas chromatography mass spectrometry (HS‐SPME‐GCMS) was performed to study the aroma volatile profile of fresh‐cut jackfruit under different storage temperature conditions (4 and 10°C). Total viable counts (TVC) and yeast and mould count (Y&M) were also simultaneously estimated. Sensory analysis revealed a loss in texture along with an increase in ripeness during storage at both the storage temperatures. It was observed that the volatile profile demonstrated significant changes at different storage temperatures during storage. Principal component analysis performed on volatile compounds allowed to differentiate fresh samples from stored samples, the differential pattern of correlation with volatiles was observed at 4 and 10°C. During storage the ester content increased linearly at both temperatures, however acetate esters predominated initially at 4°C, followed by other non‐acetate esters. In the case of 10°C storage, higher levels of ethyl ester derivatives along with other esters were obtained in the later period of storage due to enhanced microbial activity.
... The authors also reported that these bacteria were negatively correlated with acetic acid and ammonia nitrogen concentrations and positively correlated with the WSC content. Jacxsens et al. 59 reported that Pantoea agglomerans can ferment sugars to acids under anaerobic conditions and also use lactic acid, causing nutrient loss. ...
Due to the co-evolved intricate relationships and mutual influence between changes in the microbiome and silage fermentation quality, we explored the effects of Lactobacillus plantarum and Propionibacterium acidipropionici (Inoc1) or Lactobacillus buchneri (Inoc2) inoculants on the diversity and bacterial and fungal community succession of rehydrated corn (CG) and sorghum (SG) grains and their silages using Illumina Miseq sequencing after 0, 3, 7, 21, 90, and 360 days of fermentation. The effects of inoculants on bacterial and fungal succession differed among the grains. Lactobacillus and Weissella species were the main bacteria involved in the fermentation of rehydrated corn and sorghum grain silage. Aspergillus spp. mold was predominant in rehydrated CG fermentation, while the yeast Wickerhamomyces anomalus was the major fungus in rehydrated SG silages. The Inoc1 was more efficient than CTRL and Inoc2 in promoting the sharp growth of Lactobacillus spp. and maintaining the stability of the bacterial community during long periods of storage in both grain silages. However, the bacterial and fungal communities of rehydrated corn and sorghum grain silages did not remain stable after 360 days of storage.
... Toward Food Freshness Monitoring: Coordination Binding-Based Colorimetric Sensor Array for Sulfur-Containing Amino Acids INTRODUCTION To date, there is an increasing demand from consumers to evaluate the safety of food products. Freshness is the main standard for food quality assessment, including the physical form (Luo et al., 2021), the number of microorganisms (Jacxsens et al., 2003), and biochemical components (Lonchamp et al., 2009). Among the common biochemical components, sulfur-containing amino acids (SCAAs) including L-cysteine (Cys) (Cebi et al., 2017;Garcia et al., 2015), L-cystine (CySS) , DL-homocysteine (HCys) (Hoey et al., 2007), glutathione reduced form (GSH) (Xu et al., 2015), and glutathione oxidized form (GSSG) (Moreira et al., 2011) have been used as analyte markers in food samples, including wine (Valero et al., 2003), wheat flour (Reinbold et al., 2008), and fruit juice (Fracassetti et al., 2011), to evaluate food quality. ...
... Fresh produce contamination with spoilage-causing bacteria is a problem as these bacteria are able to produce metabolites that may lead to undesirable sensory characteristics and product degradation, thereby limiting shelf-life (Gram et al., 2002;Jacxsens et al., 2003;Lee et al., 2013;Ragaert et al., 2007). Here we refer to shelf-life as the amount of time a food product is considered acceptable for human consumption when stored at the appropriate storage conditions, whereas spoilage refers to a process where a food product becomes undesirable for human consumption. ...
Spinach is a highly perishable product that degrades over time, including due to bacteria contaminating the product prior to packaging, yet the dynamics of bacterial spoilage and factors that affect it are not well understood. Notably, while China is the top producer of spinach globally, there is limited available microbiological data in the literature for spinach supply chains in China. The overall goal of this foundational study was to establish a baseline understanding of bacterial population dynamics on spinach from harvest to 10 days postprocessing for a Chinese supply chain that includes distribution via traditional grocery (a local physical store) and eCommerce (an online store). To this end, organic spinach samples were collected at different stages in a Chinese supply chain by following the same 3 lots, starting at point-of-harvest through processing and distribution via a local grocery store and eCommerce. After distribution, the same 3 lots were stored at 4 °C with microbiological testing performed on multiple days up to day 10 postprocessing, simulating storage at the point-of-consumer. Results showed aerobic plate counts and total Gram-negative counts did not significantly differ across stages in the supply chain from harvest through processing. However, packaged spinach from the same processing facility and lots, exhibited different patterns in bacterial levels across 0 to 10 days postprocessing, depending on whether it was distributed via the local grocery store or eCommerce. Evaluation of bacterial populations performed on a subset of the packaged spinach samples indicated Gram-negative bacteria, in particular Pseudomonas, were predominant across all days of testing (days 0, 3, and 10 postprocessing), with populations differing at the genus level by day. Overall, this study improves our understanding of the dynamics of bacterial populations on spinach and provides baseline data needed for future studies.
... The rest of the treatments were able to maintain the ethanol level throughout ( Figure 2F). These findings are in line with other works that reported an increase in the levels of ethanol during storage in high CO 2 (10-23%) and low O 2 , which was possibly due to the microbiological activity caused by mesophilic microorganisms [60,61]. Table S1). ...
The effect of elevated CO2 in a controlled atmospheric condition (CA) on the quality attributes of fresh-cut spearmint (Mentha spicata) during refrigerated storage is investigated in the present study. Cut stems of spearmint were exposed to the continuous flow of humidified air enriched with 0 (as a control), 5, 10 and 20% CO2 during storage at 5 °C. Weight loss, leaf colour, total phenols, antioxidant activity, aromatic profile, ascorbic acid, ethanol, ammonia and ethanol-acetaldehyde concentrations were measured before and after storage for 5, 10 and 14 days. Over time, CO2 treatments increased the weight loss, surface colour, L* (from white to black) and b* (from blue to yellow) values, but lowered a* (from green to red). When compared to fresh spearmint, the lowest CO2 concentration was able to maintain the overall colour variations. The 20% CO2 treatment showed significant declines in the total phenolic content, antioxidant potential and low appearance score after 10 days, thus its quality assessment was terminated. Vitamin C levels decreased with time in all the treatments, although the 10% and 20% CO2 treatments had the lowest levels. The toxicity of the cell structures detected by the ammonia content increased and was significantly higher in all CO2 treatments. Storage in the CA with the gas composition at 5% preserved the aromatic profiles similar to those stored in air. In conclusion, increased CO2 did not improve the storability of fresh cut spearmint held at low temperatures, and the 20% gas composition had a significant negative impact on the visual quality.
... Active packaging is also another recognized innovation which involves the use of emitters and absorbers or a discharging system of active components, ethylene emitters/ scavengers and also moisture absorbers in the packaging material (Rodriguez-Aguilera and Oliveira, 2009). The active ingredients extend shelf-life by modifying the atmosphere surrounding the product inside the package (Jacxsens et al., 2003). However, the extensive use of these intelligent and active packaging methods and their practical application is limited mainly because of regulatory issues and practical limitations including high costs (Realini and Marcos, 2014;Yam et al., 2005). ...
... To date, there is an increasing demand from consumers to evaluate the safety of food products. Freshness is the main standard for food quality assessment, including the physical form (Luo et al., 2021), the number of microorganisms (Jacxsens et al., 2003), and biochemical components (Lonchamp et al., 2009). Among the common biochemical components, sulfur-containing amino acids (SCAAs) including L-cysteine (Cys) (Cebi et al., 2017;Garcia et al., 2015), L-cystine (CySS) (Chen and Li, 2019), DL-homocysteine (HCys) (Hoey et al., 2007), glutathione reduced form (GSH) (Xu et al., 2015), and glutathione oxidized form (GSSG) (Moreira et al., 2011) have been used as analyte markers in food samples, including wine (Valero et al., 2003), wheat flour (Reinbold et al., 2008), and fruit juice (Fracassetti et al., 2011), to evaluate food quality. ...
Herein, a self-assembled colorimetric chemosensor array composed of off-the-shelf catechol dyes and a metal ion (i.e., Zn²⁺) has been used for the sulfur-containing amino acids (SCAAs; i.e., glutathione, glutathione disulfide, L–cysteine, DL–homocysteine, and L–cystine). The coordination binding–based chemosensor array (CBSA) fabricated by a competitive assay among SCAAs, Zn²⁺ ions, and catechol dyes [i.e., pyrocatechol violet (PV), bromopyrogallol red (BPR), pyrogallol red (PR), and alizarin red S (ARS)] yielded fingerprint-like colorimetric changes. We succeeded in the qualification of SCAAs based on pattern recognition [i.e., a linear discrimination analysis (LDA)] with 100% correct classification accuracy. The semiquantification of reduced/oxidized forms of SCAAs was also performed based on LDA. Furthermore, we carried out a spike test of glutathione in food samples using the proposed chemosensor array with regression analysis. It is worth mentioning that we achieved a 91–110% recovery rate in real sample tests, which confirmed the accuracy of the constructed model. Thus, this study represents a step forward in assessing food freshness based on supramolecular analytical methods.
... After the addition of cellulase, the dominant genus shifted from Lactococcus (30 days) to Lactobacillus (60 days) [22]. Jacxsens et al. revealed that Pantoea would be metabolized to produce acetic acid, propionic acid, and succinic acid [23]. Enterobacteriaceae is also capable of producing carbohydrate metabolism under anaerobic conditions. ...
Background
The objective of this study was to evaluate the chemical compositions and microbial communities of salt-tolerant alfalfa silage. Salt-tolerant alfalfa was ensiled with no additive control, and cellulase for 30 and 60 to 90 days. In this study, the dry matter (DM) content of the raw material was 29.9% DM, and the crude protein (CP) content of the alfalfa was 21.9% CP.
Results
After 30 days of fermentation, the DM content with the cellulase treatment was reduced by 3.6%, and the CP content was reduced by 12.7%. After 60 days of fermentation, compared with alfalfa raw material, the DM content in the control group (CK) was reduced by 1%, the CP content was reduced by 9.5%, and the WSC (water-soluble carbohydrates) content was reduced by 22.6%. With the cellulase, the lactic acid content of the 30- and 60-day silages was 2.66% DM and 3.48% DM. The content of Firmicutes in salinized alfalfa raw material was less than 0.1% of the total bacterial content. Before and after ensiling, the microbes had similar composition at the phylum level, and were composed of Firmicutes , Actinobacteria , Bacteroidetes, and Proteobacteria . The abundance of Pantoea was dominant in fresh alfalfa. In the absence of additives, after 30 days and 60 days of silage, the dominant lactic acid bacteria species became Lactococcus and Enterococcus .
Conclusions
The results showed that LAB ( Lactobacillus , Lactococcus , Enterococcus, and Pediococcus ) played a major role in the fermentation of saline alfalfa silage. It also can better preserve the nutrients of saline alfalfa silage. The use of cellulase enhances the reproduction of Lactobacillus . The fermentation time would also change the microbial community of silage fermentation.
... Lactic acid bacteria (LAB) are relevant spoilage-causing bacteria in vacuum-packed and modified atmosphere packed food, where sensorial spoilage due to growth of homofermentative LAB and acid production will usually be detectable when the numbers exceed 10 7 CFU/g (Jacxsens et al., 2003). In cases where growth of heterofermentative species at such high levels occurs, off-odour, slime and gas formations may develop. ...
A risk-based approach was developed to be followed by food business operators (FBO) when deciding on the type of date marking (i.e. 'best before' date or 'use by' date), setting of shelf-life (i.e. time) and the related information on the label to ensure food safety. The decision on the type of date marking needs to be taken on a product-by-product basis, considering the relevant hazards, product characteristics, processing and storage conditions. The hazard identification is food product-specific and should consider pathogenic microorganisms capable of growing in prepacked temperature-controlled foods under reasonably foreseeable conditions. The intrinsic (e.g. pH and a w), extrinsic (e.g. temperature and gas atmosphere) and implicit (e.g. interactions with competing background microbiota) factors of the food determine which pathogenic and spoilage microorganisms can grow in the food during storage until consumption. A decision tree was developed to assist FBOs in deciding the type of date marking for a certain food product. When setting the shelf-life, the FBO needs to consider reasonably foreseeable conditions of distribution, storage and use of the food. Key steps of a case-by-case procedure to determine and validate the shelf-life period are: (i) identification of the relevant pathogenic/spoilage microorganism and its initial level, (ii) characterisation of the factors of the food affecting the growth behaviour and (iii) assessment of the growth behaviour of the pathogenic/spoilage microorganism in the food product during storage until consumption. Due to the variability between food products and consumer habits, it was not appropriate to present indicative time limits for food donated or marketed past the 'best before' date. Recommendations were provided relating to training activities and support, using 'reasonably foreseeable conditions', collecting time-temperature data during distribution, retail and domestic storage of foods and developing Appropriate Levels of Protection and/or Food Safety Objectives for food-pathogen combinations.
... These values were lower than the critical limit for total microbial loads of vegetables (8.0 log CFU/g) (JACXSENS et al., 2002). YM values increased from 1.3 to 5.2 log CFU/g, overcoming the critical limits of 5 log CFU/g for yeasts (JACXSENS et al., 2003) after 12 days of storage. Increased trend in microbial counts of TAB and YM throughout the storage of fresh-cut papaya were also reported by Gonzalez-Aguilar et al. (2009) andWAGHMARE andANNAPURE (2013), correlated to the packaging systems, storage temperatures and different cut types of fresh-cut fruits. ...
In this study, the effects of cold storage (5±0.5°C and relative humidity of 90±1%) on the quality of fresh papaya slices packed in a passive atmosphere with a semi-permeable film were evaluated. Physico-chemical traits such as total soluble solids, reducing sugar, pH increased during storage as well as the polyphenols, carotenoid content and antioxidant activity that reaching the highest values at end of trials. Changes in colorimetric parameters resulted in a significant decrease after 4 days of hue angle values, which then remained constant. The cutting process enhanced the antioxidant enzymes activity such as superoxide dismutase, catalase and ascorbate peroxidase. The analysis of the main components showed physical-chemical, qualitative, and enzymatic changes in papaya samples during cold storage, showing a shift from negative to positive values along the PC1 and indicating a qualitative decay of sliced papaya.
... Durante esse período foram analisados nos tempos 0; 3; 6; 9; 15 dias de armazenamento quanto as medidas do parâmetro cor realizadas utilizando colorímetro digital (HunterLab) e escala CIELAB (sistema de Munsell); sólidos solúveis totais (expressos em °Brix), obtidos utilizando um refratômetro digital de bancada modelo HI 96801, segundo a metodologia descrita pelo Instituto Adolfo Lutz (2008); pH, determinado através do método potenciométrico, onde utilizou-se um pHmetro, modelo PHS-3B; acidez titulável, determinada pelo método de titulação volumétrica com indicador até o ponto de viragem com solução de NaOH 0,1 N, segundo metodologia descrita pelo Instituto Adolfo Lutz (2008); porcentagem de perda de massa, calculada pela diferença entre a massa inicial das embalagens com o minimamente processado e aquela obtida em cada dia de avaliação. ...
... Durante esse período foram analisados nos tempos 0; 3; 6; 9; 15 dias de armazenamento quanto as medidas do parâmetro cor realizadas utilizando colorímetro digital (HunterLab) e escala CIELAB (sistema de Munsell); sólidos solúveis totais (expressos em °Brix), obtidos utilizando um refratômetro digital de bancada modelo HI 96801, segundo a metodologia descrita pelo Instituto Adolfo Lutz (2008); pH, determinado através do método potenciométrico, onde utilizou-se um pHmetro, modelo PHS-3B; acidez titulável, determinada pelo método de titulação volumétrica com indicador até o ponto de viragem com solução de NaOH 0,1 N, segundo metodologia descrita pelo Instituto Adolfo Lutz (2008); porcentagem de perda de massa, calculada pela diferença entre a massa inicial das embalagens com o minimamente processado e aquela obtida em cada dia de avaliação. ...
Mexico ranks the fourth place of this fruit world production and it’s the first one in exportation, giving commercial priority to the primary sector of the agribusiness chain. 80% of the secondary sector is limited by generating differentiated products, this is
due to the restriction that technological development has. In the context of the mango processing industry, significant volumes of rubbish are generated, during transformation 28 to 43% of the total is discarded as waste. e present investigation objective was to
evaluate physicochemical characteristics and determinate sensorial characteristics degree of acceptance of discard Ataulfo mango fruits in Acapetahua municipality of Chiapas, Mexico for their potentially approach glimpse. For the evaluation were collected 200 discarded and quality Ataulfo mango fruits, physicochemical and sensorial variables were estimated. One-way analysis of variance (ANOVA) was used for statistical comparison continued by a Tukey test P≤0.05, discarded mango sensorial parameters were handle in a descriptive way. Significant statistical difference was found in firmness, coloration, total ashes and raw fiber of the pulp as part of the physicochemical variables. Discarded mango peel doesn’t comply approach specifications by damage and defects.
Physicochemical composition of discarded and quality mango peel results similar. Discarded mango pulp sensorial attributes (I like it to much and I like it) had the highest percents. Physicochemical and sensorial characteristics found in pulp of discard mango
make it able for it approach in Mango Agroalimentary Chain secondary sector.
... Dutkiewicz et al. (2016) recently demonstrated that Pantoea could inhibit the growth of Escherichia coli and fungi. Jacxsens et al. (2003) reported that Pantoea agglomerans can produce acetic acid, propionic acid, FIGURE 6 | A co-occurrence network analysis among the different microbiota and metabolites from the comparisons between the CON group and FRU group (A) and between the CON group and PEC group (B). Each co-occurring pair among microbial populations at the genus level and metabolites has an absolute Spearman rank correlation above 0.94 [red straight line, positive correlation (r ≥ 0.94); blue dotted line, negative correlation (r ≤ -0.94)]. ...
This study explored the effects of four sugar source treatments, including no sugar (CON), fructose (FRU), pectin (PEC), and starch (STA), on the microbiota and metabolome of alfalfa (Medicago sativa) silage. The bacterial community was determined via 16S rRNA gene sequencing. The metabolome was analyzed using ultra high-performance liquid chromatography tandem time-of-flight mass spectrometry (UHPLC/TOF-MS). After 60 days of fermentation, the pH values in FRU and PEC were lower than those in STA and CON. FRU had a greater lactic acid concentration compared to STA and CON. Weissella (47.44%) and Lactobacillus (42.13%) were the dominant species in all four groups. The abundance of Pediococcus was lower, and the abundance of Leuconostoc, Pantoea, and Microbacterium was higher, in FRU compared to CON. The abundance of norank_f__Bacteroidales_S24-7_group was higher, and the abundance of Turicibacter was lower, in both FRU and PEC than in CON. Leuconostoc was negatively correlated with the pH value, and Pediococcus was positively correlated with the pH value. No microbiomes were detected as discriminative features between STA and CON. The addition of FRU and PEC presented more peptides, such as Leu–Val–Thr, Leu–Phe, Ile–Pro–Ile, Val–Trp, and Ile–Leu–Leu but a lower abundance of metabolites for triterpene glycosides including sanchinoside B1, medicagenic acid, betavulgaroside IV, and prosapogenin compared to CON. The addition of PEC presented more phenyllactic acid compared to CON. Our study demonstrated that the addition of pectin and fructose improved the quality of alfalfa silage mainly by promoting Leuconostoc, Pantoea, and Microbacterium, and inhibiting Pediococcus in FRU, and promoting norank_f__Bacteroidales_S24-7_group and inhibiting Turicibacter in both FRU and PEC; this was due to altered metabolic profiles resulting from antifungal activity and decreased triterpene glycoside accumulation. This study improves our understanding of ensiling mechanisms related to the contributions of sugar.
... However, pH value of control fruits have not statistically differed from treatment 2.5% EAP and 1.5% EAqP (3.93 and 3.90, respectively). This lower pH value in 'Eva' for 2.5% EAqP treatment may be related to the greater conservation in storage and/ or decrease of microbial contamination due to propolis action, as according to Jacxsens et al. (2003) the microbiota (bacteria) actively participates in plants degradation, resulting the increase of pH, result of protein breakdown and compounds release. These results corroborate with Izumi et al. (1996), who associated pH increase in minimally processed zucchini with microbiological contamination. ...
The objective of this study was to evaluate the efficacy of different propolis extracts in post harvesting ‘EVA’ organic apple, in order to prolong storage and fruit quality maintenance. After selection, fruits were sanitized with vinegar (6%) solution, dried in the air and immersed in propolis solution for 1 minute when it has been possible. Treatments were T1: Control without application; T2: 1.5% propolis alcoholic extract (1.5% EEP); T3: 2.5% propolis alcoholic extract (2.5% EEP); T4: 1.5% aqueous propolis extract (1.5% EAqP) and T5: 2.5% aqueous propolis extract (2.5% EAqP). Fruits were packed in rigid plastic boxes and stored in a cold room with temperature of 5 ± 1 °C and 85 ± 1% RH for 80 days. Every 10 days some traits were evaluated as fruit weight loss (%), respiratory activity (mL of CO2 kg of fruit-1 hour-1), luminosity, chroma, Hue angle, pH, soluble solids (°Brix), titratable acidity (g of malic acid 100g-1) and reducing and non-reducing sugars. The experimental design was completely randomized in a factorial scheme and data were submitted to F test (p <0.05) and significant interactions were deployed via regression analysis. The application of propolis extract (aqueous and alcoholic) in ‘Eva’ organic apple post-harvest does not prolong refrigerated storage (5 ± 1ºC and 85 ± 1% RH) and does not influence in fruit quality conservation.
... It has been reported that 3-methyl-1-butanol could be considered a possible indicator of fish spoilage or loss of freshness during storage in ice (Soncin, Chiesa, Panseri, Biondi, & Cantoni, 2009). Moreover, 3-methy-butanol is associated with microbial catabolic pathways of leucine (Berry, 1998;Laursen, Leisner, & Dalgaard, 2006;Mejlholm, Boknaes, & Dalgaard, 2010) and has been considered responsible for the formation of nauseating and musty odors (Jacxsen et al., 2003). Here, the content of 3-methyl-butanol was relatively high in the white croaker at the beginning of storage, suggesting differences in microbial composition between the two fish species in the early stage of cold storage. ...
White croaker and small yellow croaker both belong to the fish family Sciaenidae, but their economic value and odor characteristics are quite different. In this study, electronic nose and gas chromatography–mass spectrometry were utilized to explore the odor characteristics of the two stored for different refrigeration periods. The results showed that their odor profiles could be clearly distinguished by principal component analysis. Compounds associated with fresh white croaker were found to be more complex than smaller yellow croaker through the load graph, while the result was opposite in later cold storage. The absolute peak areas of compounds like trimethylamine and 3‐methyl‐butanol were 6.42 and 1.42, respectively, in the white croaker, which were higher than in the small yellow croaker at the first day of refrigeration. And compound such as indole was first produced in white croaker during late cold storage. However, there were more compounds related to spoilage in the small yellow croaker; compounds like phenylethyl alcohol and benzeneacetaldehyde were not detected in the white croaker.
Practical applications
White croaker and small yellow croaker are almost indistinguishable in appearance, especially after being cooked. But there are vast differences in their meat quality and odor characteristics, which affect their commercial values. As a result, a lot of white croakers are dyed and sold as small yellow croakers, although this does not change their eating or odor qualities. Principal component analysis of the odor characteristics of the two species of fish stored for different periods of refrigeration might provide some scientific basis for exploring the causes of their economic value differences.
... Several authors have in fact noted the association between LAB growth and spoilage of fresh-cut fruits including pineapples when stored at 7 °C or above in a modified atmosphere. 23,24,25 Staphylococcus aureus from MPW and MPC pineapples was consistently undetectable by plating (< 2 Log CFU/g), hence data are not shown. Even though staphylococci have been found on fruits and vegetables during processing, they are generally unable to proliferate in the presence of the more dominant lactic biota and this may explain the poor isolation of staphylococci. ...
Pineapple is one of the most economically important fruit crops of Mauritius and is often sold after being minimally processed (MP). Unfortunately, minimally processed whole (MPW) and fresh-cut (MPC) pineapples are susceptible to microbial contamination that can compromise the quality of the products. It is therefore important that MP pineapples have optimal freshness, nutritional quality, and are free from microbial contamination which would otherwise constitute a public health hazard to the consumers. The main aim of this study was to assess the microbiological, nutritional, and physicochemical quality of MP pineapples sourced from wet markets and supermarkets. Samples of MPW and MPC pineapples collected from open markets and supermarkets were subjected to microbiological, pH, and vitamin C analyses. The MP pineapples were also challenged using the specific spoilage organism (SSO), Pseudomonas fluorescens and subsequently stored at either ambient or refrigeration temperature to simulate storage conditions of wet markets and supermarkets, respectively. Laboratory analyses revealed that the Total Viable Counts (TVC), pH, and vitamin C content for MPW and MPC pineapples sampled ranged from 4.8 - 5.5 Log CFU/g, 4.16 - 4.96, and 21.60 - 28.90 mg/100 g, respectively. Since the population density of TVC was less than 7 Log CFU/g, which usually marks the onset of microbiological spoilage, the products were considered to be of a satisfactory microbiological quality. Moreover, there was no statistically significant difference in the microbiological load, pH, and vitamin C content for pineapples sourced from markets and supermarkets. Taken together, this study reveals that MP pineapples sold in wet markets and supermarkets have a satisfactory microbiological, nutritional, and sensorial quality with a shelf-life of >7 hours and >5 days when stored at room (29°C) and refrigeration (4°C) temperatures, respectively.
... However, no significant difference was observed between the combined treatment with SAEW and AEW at 4°C. The difference in SI could be caused by the presence of different species of TVC with different metabolic activities and sensory quality deterioration depending on the type of fresh products (Jacxsens et al. 2003). The pH values of meat samples ranged from 4.33 to 5.58 after the EW treatment and did not differ remarkably between the treatments during 8 days of storage at 10°C. ...
Foods of animal origin, such as red meat and poultry products, are primary sources of superior protein for humans. With the production and consumption of these products increasing rapidly in recent decades, microbial safety and food quality are vital issues. Electrolyzed water (EW) as a sanitizer has awakened high interest in the food industry of many countries. The use of EW to decontaminate fresh red meat, ready-to-eat meat, poultry and shell eggs has been effective in reducing pathogenic microorganisms. Moreover, EW presents many advantages over traditional decontaminants; it provides effective antimicrobial activity and is environmentally friendly, simple to handle and relatively inexpensive. However, no complete elimination of pathogens on red meat and chicken meat was obtained after treatment of the meats with EW. This result probably occurs because organic matter and blood residue were present. This chapter provides a brief overview of how EW treatment affects foods of animal origin, especially the microbial safety and the physicochemical and sensory qualities of the food.
... Moreover, the high level of acetic acid and propionic acid in wilted silage may be important for aerobic stability (Zhang et al., 2016b); this issue requires further research. Jacxsens et al. (2003) reported that Pantoea agglomerans can produce acetic acid, propionic acid, and succinate, and these Enterobacteriaceae are able to ferment sugars to acids under anaerobic conditions. The relative abundance of Enterobacteriaceae (especially Pantoea) was relatively high in wilted silage in the present experiment (Figure 4), which may explain the increases in both organic acids. ...
The objective of this study was to evaluate the effects of wilting and Lactobacillus plantarum (LP) addition on the silage fermentation quality and microbial community of Moringa oleifera Lam. leaf silage. Unwilted (direct-cut) or wilted M. oleifera leaves were prepared either with or without LP (1.0 × 10⁶ cfu/g) followed by either 60 or 120 days of ensiling, leading to eight treatment groups. The results showed that lactic acid was the dominant fermentation product, and no butyric acid was detected for any of the treatments. Higher acetic acid and propionic acid were detected during the fermentation of wilted silage compared to unwilted silage. Although NH3-N content increased after wilting, the content was far below 10% of the dry matter (DM). In addition, higher pH was observed after 120 days of ensiling compared to 60 days. Wilting also influenced the bacterial community structure. Lactobacillus was the most dominant genus in unwilted samples while Enterobacteriales, Weissella, and Pantoea were the most dominant genera in wilted samples. Furthermore, the relative abundance of undesirable microorganisms was far below that of lactic acid bacteria in all treatments. In summary, wilting had significant effects on fermentation quality, and it was shown that M. oleifera leaves can undergo quality ensiling directly without the addition of LP.
... This is indicated by generation of off-flavor and enhanced production of CO 2 (Baldwin et al., 1999;Han, 2005). The increase in the CO 2 composition in control and alginate treated berries can be attributed to the production of CO 2 , ethanol, organic acids produced by spoilage microbes (Jacxsens, Devlieghere, Ragaert, Vanneste, & Debevere, 2003). ...
Strawberries are highly demanded fruits because of their color, nutritional values and appearance. The aim of this study was to develop and characterize alginate and limonene liposomes as edible coating materials and to determine their efficacy in shelf life extension and maintaining quality parameters of ‘Chandler’ strawberries. Alginate solution (1.5% w/v) and Limonene liposomes prepared from 80% lecithin and 20% PDA were used as edible coating materials. Fungal decay percentage, total yeast and mold counts, headspace atmosphere analysis, total soluble solids, pH, titratable acidity, total anthocyanin content and total phenolics were analyzed to assess fruit quality during 14 days at 4 °C of storage. Days of storage was found to be significant in maintaining the quality of the strawberries. Among the coating types, limonene liposomes were found to be significantly more effective in maintaining the lower concentration of carbon dioxide (CO2), lower the change in pH (3.9), and had higher total anthocyanin (43.85) content during storage than those without a liposomal coating. Thus, limonene liposomes were found to be useful for extending the shelf life and maintaining quality of strawberry fruits.
... After 7 and 14 days the CO 2 concentration in the containers with chitosan-coated melon plugs was significantly lower as compared to the containers with non-coated ones. The enhanced CO 2 accumulation upon prolonged storage of fresh-cut products is associated with microbiological factors such as spoilage bacteria and yeasts (Jacxsens, Devlieghere, Ragaert, Vanneste, & Debevere, 2003). Therefore, the antimicrobial effect of chitosan coating resulted in a reduction in the CO 2 accumulation. ...
... Packing materials can be divided into three main groups: metal, glass, and plastic. The correct combination of them can produce adequate weight and gas composition within a package, which may maintain the quality and safety, and extend the product's shelf life (Jacxsens, Devlieghere, Ragaert, Vanneste, & Debevere, 2003). ...
Unit operations modify material properties aiming to produce uniform and high-quality food products with greater acceptance by the increasingly demanding consumers or with longer shelf life and better possibilities of storage and transport. Microorganisms, including bacteria, molds, viruses, and parasites, may have different susceptibilities to unit operations employed during food processing. On-farm (cleaning, selection and classification, cooling, storage, and transport) and on-factory unit operations (heating, refrigeration/freezing, dehydration, modification of atmosphere, irradiation, and physical, chemical, and microbial-based operations) are commonly employed throughout food production chain. The intensity and combination of unit operations along with food composition, packaging, and storage conditions will influence on the dominance of specific microorganisms, which can be pathogenic or responsible for spoilage. Thus, in the context of food safety objective (FSO), the knowledge and the quantification of the effects caused by each step of processing can enable to control and ensure the quality and safety of manufactured products.
... and Lactococcus spp. have been identified as common spoilers under anaerobic conditions in fresh produce (Jacxsens et al., 2003;Paillart et al., 2017;Pothakos et al., 2014b;Ragaert et al., 2007). Additionally, psychotrophic representatives of these genera have been associated with cases of spoilage, especially in Belgium (Pothakos et al., 2014c). ...
Fresh cut iceberg lettuce spoilage was studied considering the microbial and biochemical activity, the formation of volatile organic compounds (VOC) and consumer acceptability. Lettuce was packaged under three different packaging conditions and stored at 4 °C for 10 days: anaerobic packaging (ANAER), equilibrium modified atmosphere packaging with 3% O2 (EMAP) and perforated packages (AIR).
Results indicated a clear distinction between packaging conditions. EMAP and AIR resulted in a short shelf life (≤5.6 days) which was limited due to browning, leading to consumer rejection as assessed via the Weibull hazard analysis method, while no off-odors were detected. Culture- independent 16 s rRNA gene amplicon sequencing revealed Pseudomonas spp. as the dominating species. In contrast, under ANAER conditions, lactic acid bacteria dominated with genera of Leuconostoc spp. and Lactococcus spp. proliferating, while also oligotypes of Pseudomonas spp. were found. Spoilage under ANAER occurred after 6.6 days and it was related to strong fermentative-like off-odors that were present by the end of storage. As revealed by selective ion flow tube mass spectrometry (SIFT-MS), these odors were associated with several VOCs such as: ethanol, 3-methyl-1-butanol, 2,3-butanediol, (Z)-3-hexen-1-ol, hexanal, acetic acid, ethyl acetate and dimethyl sulfide. Panelists rejected the iceberg lettuce due to the formation of off-odors while the overall appearance remained good throughout the study. Hence a sensor based technology incorporated in the packaging, detecting VOCs and in particular ethanol as dominant compound, could serve as a spoilage indicator for ANAER packed lettuce, which proved to have the longest shelf life.
... Microbial spoilage including off-flavor formation, slimy surface, wetness and soft rot, discoloration, and visual microbial growth/colonies has been used as a main or exclusive objective criterion to determine shelf life of fresh-cut products (O'Connor-Shaw et al., 1994; Sapers et al, 2001,). Jacxsens et al. (2003) reveal that green, yellow and red bell pepper was unacceptable by day 6 of storage under atmospheric condition of 7°C due to acidic flavor, water loss and texture change. Also, Allende et al. (2004) indicate that processed Lollo Rosso lettuce had a shelf life shorter than 7 days at 5°C due to high microbial counts and off-odor formation under MAP. ...
Against the background that leafy vegetables stored under ambient conditions are influenced by environmental factors which may cause significant quality loss in terms of freshness, colour, texture and composition, the iceless cooler was used to evaluate microbial load of leafy vegetables. The samples were evaluated for bacterial (coliforms and mesophiles) and fungal (mold and yeast) loads. Results of the microbial test showed that Corchorus olitorius had highest mean microbial load with plate count of 6.7 x 104 CFU/g and Hibiscus sabdariffa had the least mean microbial load with plate count of 4.8 x 104 CFU/g after five days of storage. Corchorus olitorius show a significant increase of Escherichia coli, Staphylococcus aureus and Streptococci species after five days of storage. The ANOVA results showed that vegetables stored under ambient conditions were significantly different (p˂0.01) from those stored in the iceless cooler. The results also indicate that Amaranthus dubius recorded the highest mean weight of 1.94kg and maintained its freshness and colour for up to three days compared with Corchorus olitorius with the least weight of 1.84kg.
... The two most used protection technologies for minimally processed vegetables are low temperature and controlled (CA) or modified (MA) atmospheres. Several studies have shown that low levels of O 2 in combination with high levels of CO 2 can reduce respiration rates, control microbiological growth and prolong shelf-life of the product (Day B.P.F., 1993;Watada et al., 1996;Jacxens et al., 2003;Allende et al., 2004). ...
Minimally processed table grapes have traditionally been used as a component of fruit salads; only recently has been taken into account the possibility of producing single-portion packages in small containers. The aim of this research was to assess the shelf-life of small table grape clusters, including some of the most utilized varieties in Italy, such as ‘Vittoria’, ‘Superior seedless®’, ‘Italia’, ‘Crimson seedless’, ‘Red Globe’ and ‘Black Pearl’, packed in polyethylene containers. Chemometric techniques including principal component analysis (PCA) and linear discriminant analysis (LDA) were carried out on six parameters to develop discriminant models. The berry firmness remained satisfactory until the 15th day of storage, especially in seedless cultivars such as ‘Superior seedless®’ and ‘Crimson seedless’. Variations of weight loss and colour were almost absent in all cultivars. A significant increase in CO2 and a decrease in O2 inside the packages were observed during the second week of storage. During the cold storage period, most of the quality parameters remained stable in all cultivars. LDA achieved satisfactory discrimination of grape fruits according to the variety and the storage time. The results indicated the possibility of packaging small clusters of table grapes that could maintain good quality parameters for a rather long storage period without excessive reduction of the antioxidant activity of the product.
... Among others, visible properties of fresh-cut fruit and vegetable commodities are one of the most important parameters to evaluate the total quality of the product by consumers. Suitable packaging helpa to reduce discoloration such as enzymatic browning of cut surfaces, yellowing of green vegetables and pale color of bright vegetables, mechanical damage including foiled lettuce leaves and absence of cutting damage, as well as decay (Bolin and Huxsoll,1991;Jacxsens et al., 2003;Varoquaux and Wiley, 1994). Storage temperature is the single most important factor affecting spoilage of minimally processed fruit and vegetables. ...
... Also, the model highlighted that the use of CO 2 had a promoting effect on L. innocua on cut lettuce but an inhibiting effect in vitro. Jacxsens et al. (2003) related the microbial quality and the corresponding production of non-volatile compounds and related sen sory disorders. By using the Baranyi model the authors showed that the outgrowth of lactic acid bacteria and yeasts can be evaluated by detecting the non-volatile compounds. ...
... Para os teores de clorofila e carotenoides a extração foi feita utilizando-se o método de Arnon (1949). Os cálculos foram feitos segundo Lichtenthaler (1987 (Jacxsens et al., 2003). ...
The objective of this study was to evaluate the efficacy of sanitization with hydrogen peroxide in reducing the enzymatic browning and pathogens of fresh cut snap bean. Fresh cut snap beans were inoculated by immersion in an Escherichia coli and Salmonella enteritidis contaminant solution Then, the vegetable was sanitized with hydrogen peroxide (0; 5; 10 and 20 mL L-1) for 10 minutes. The pathogens were monitored immediately after sanitization and after 4 days of storage at 10ºC. In other similar experiment, but without inoculation of pathogens, the snap bean were evaluated periodically. The surface color, pH, activity of phenylalanine ammonia-lyase, peroxidase and polyphenoloxidase enzymes, chlorophyll and carotenoids contents were evaluated. The sanitization with hydrogen peroxide reduced the count of E. coli and S. enteritidis, being similar for different hydrogen peroxide concentrations. The browning of the section surface of snap bean was controlled by hydrogen peroxide in the concentration of 20 mL L-1. The activity of the enzymes as well as the pigments content (chlorophyll and carotenoids) were not affected by treatments, except the polyphenoloxidase enzyme. The pH increased during storage and was greatest in snap bean sanitized with 20 mL L-1. The sanitization with hydrogen peroxide is effective in reducing population of E.coli and S. enteritidis and minimizing browning in fresh cut snap bean, but caused spots on the vegetable skin, precluding its use.
Due to spoilage microflora and browning, minimally processed fresh-cut fruits have a short shelf life, and over the years, studies have shown the potential of using edible coatings to extend the shelf life and improve the safety of fresh-cut fruits. Recently, there has been a rise in research on the incorporation of probiotics in edible coatings due to the bespoke health and biopreservation benefits they impart. Therefore, in this study, lactobacillus strains (Lactiplantibacillus plantarum 75 and Bifidobacterium longum) were incorporated into a xanthan edible coating to enhance color retention, sensory properties, antioxidant retention (ascorbic acid, carotenoids, total phenols), and antioxidant activity (FRAP antioxidant power, ABTS scavenger activity) of fresh-cut cantaloupes and honeydew cucumis melo L. melons during cold storage at 5 C and 85% RH for five days. The edible coating was prepared by mixing 0.5% xanthan gum, 1% glycerol, and 2% citric acid solution with L. plantarum 75 (LAB 75) and Bifidobacterium longum bacteria separately, and the final lab count for each strain was made to be 8.0 log CFU/mL. Stable probiotic coatings with ζ-potential of between −39.7 and −51.4 mV and a PdI of 1 were developed, and the incorporation of the probiotic bacteria into the coating was justified using FTIR analysis. The probiotic coatings showed a typical pseudoplastic behavior, in which the viscosity curves fall as the shear rate increases. Thermal stability analysis showed a continuous and multi-step weight reduction in this work, illustrating how the edible coating components interact. The survival of both Lactobacillus strains was recorded on day 5. Both freshly cut melons coated with xanthan and loaded with Lactobacillus strains retained a sufficient quantity of probiotics at the end of storage, while L. plantarum 75 (7 log CFU/g for cantaloupe and 8 log CFU/g for honeydew) retained the highest viability compared to B. longum (6 log CFU/g for cantaloupe and 7 log CFU/g for honeydew). In comparison to the coated and uncoated control samples, the inclusion of L. plantarum 75 in xanthan coatings significantly retained the color properties, pigments (total chlorophyll and carotenoids), ascorbic acid, total phenols, and antioxidant activity (FRAP, DPPH, and ABTS). The overall acceptability of fresh cuts of cantaloupe and honeydew melons coated with xanthan gum loaded with L. plantarum 75 was higher than that of other treatments. Thus, xanthan gum loaded with L. plantarum 75 coating is most suitable for reducing postharvest losses in fresh cuts of honeydew melons and cantaloupe, which will help preserve antioxidant and bioactive properties. The xanthan gum loaded with L. plantarum 75 coatings exhibited the highest preservation impact; therefore, it can be recommended for the fresh-cut industry.
Lactic acid bacteria (LAB) and their metabolites such as bacteriocins have gained considerable interest in terms of their bio-preservative properties to improve food safety and quality. In this study, a quantitative proteomic investigation employing stable isotope labeling by peptide demethylation was carried out to investigate changes in intracellular proteins of bacteriocin-like substance (BLS) producing Lactococcus spp. 7.17 grown in vegetable or fruit juice culture media at 10 °C for 0, 3 or 7 days. In total, 1053 proteins in vegetable medium and 1113 in fruit medium were identified and quantified. Proteins that changed more than two- fold were identified as increased or decreased ones and grouped into four clusters. Those increased proteins were involved in the events of low temperature and ROS stress responses, DNA processing, transcription and translation, central carbon metabolism, fatty acid and phospholipid metabolism, amino acid and cell wall biosynthesis. Key proteins in relation to BLS producing property were also identified suggesting that at least one bacteriocin IIa production system exists in Lactococcus spp. 7.17. These findings provide insights into protein changes of L. lactis at low temperature and lay foundations for further investigations on BLS producing LAB using targeted quantitative proteomic approaches. SIGNIFICANCE OF THE RESEARCH: The inhibitory effects of Lactococcus spp. 7.17 on Listeria innocua in fruit and vegetable juice culture media were confirmed. Using a quantitative proteomic approach employing stable isotope labeling by peptide demethylation, 99 or 113 significantly changed proteins of Lactococcus spp. 7.17 grown in vegetable or fruit juice medium were determined, respectively. The significant change in protein abundance suggested an adaptive mechanism of Lactococcus spp. to culture condition at low temperatures. This research provides insights on protein changes of Lactococcus spp. which has potential application in fresh and fresh-cut fruit and vegetables at low temperature.
The application of chemical disinfectants in postharvest food processing facilities is important for the control of foodborne pathogen outbreaks. Similar to drinking water disinfection, food processors will need to optimize disinfectant exposures to balance pathogen inactivation against exposure to potentially toxic disinfection byproducts (DBPs). Since most disinfection research has focused on drinking water, this review summarizes research related to disinfection in food washing facilities, particularly by chlorination and ozonation. Although these disinfectants are also used for drinking water, the conditions are significantly different at food processing facilities. After a brief summary of foodborne pathogen outbreaks, this review describes food processing treatment trains, particularly the critical differences in conditions encountered relative to drinking water disinfection (e.g., short disinfectant contact times and high and variable disinfectant demands). The review discusses research related to pathogen inactivation and DBP formation by chlorine and ozone during washing of produce, meat and seafood. In particular, the research highlights the difficulty of inactivating pathogens on food, but the efficacy of these disinfectants for controlling pathogen cross-contamination through the washwater. While most research on food-associated DBPs has focused on the same, low molecular weight DBPs of interest in drinking water, these DBPs partition to the washwater. This review highlights the need for research on the initial transformation products of disinfectant reactions with biomolecules, since these products may present a risk for consumer exposure by remaining within the food.
Aims
To identify the main spoilage bacterium on fresh-cut leafy vegetables and establish a multiplex PCR assay.
Methods and results
Based on physiological-biochemical, molecular identification, and artificial contamination tests, the main bacterium to spoil fresh-cut leafy vegetables was identified as Exiguobacterium spp. and Exiguobacterium acetylicum. Comparative genomics showed that P401_RS0117025 and oxi_50,582,462 genes are specific to Exiguobacterium spp. and E. acetylicum. Based on this, three pairs of primer sets to EaG-291, EaS-2B, and Ea16S-12 genes were designed and used to develop a multiplex PCR assay, which exhibited 100% specificity among 16 Exiguobacterium and 10 non-Exiguobacterium strains. Finally, 84 fresh-cut leafy vegetable samples were analyzed by multiplex PCR assay and standard physiological-biochemical experiments, the results showed multiplex PCR assay reached a detection rate of 96%.
Conclusions
The main spoilage bacterium was identified as Exiguobacterium spp. and E. acetylicum on fresh-cut leafy vegetables based on the novel specific genes explored in this study.
Significance and impact of study
A rapid, specific, and sensitive PCR assay was developed for the detection of Exiguobacterium spp. and E. acetylicum.
Open refrigerated display cases in supermarkets are prevalent in the United States despite being prone to temperature fluctuations. We collaborated with a chain retailer in Florida to retrofit existing open vegetable display cases with doors, and monitored the display temperature profile over 5 months. Quality evaluations were performed on baby spinach, spring mix, and chopped romaine lettuce after storage under simulated open and closed case conditions. Doors improved spatial and temporal temperature uniformity in whole and fresh-cut vegetable cases. Optimal storage temperature for ready-to-eat produce (≤5 °C) was recorded over 98% of the time after door installation versus 49–88% before retrofitting. An overall temperature decrease in the fresh-cut produce case from 3.62 to 0.66 °C necessitated a thermostat setting adjustment of +1.1 °C to avoid freezing of salad product. Elevated headspace CO2 concentrations and higher populations of aerobic bacteria (6.6 log CFU g⁻¹), yeasts and molds (4.6 log CFU g⁻¹) were found under open display conditions for one or more salad products tested. Baby spinach leaves from the open case environment were lighter green and more yellowish in color. Electrolyte leakage and ascorbic acid content of the three salad types were similar between the open and closed door displays. Superior overall visual quality and stronger purchase intent were found for baby spinach and spring mix samples from the closed display case. These products had less severe off-odor and discoloration, and crispier texture than those held in the open case. The decreased overall temperature and improved temperature uniformity in closed display cases, along with better produce quality and potential energy savings, may encourage retailers to consider retrofitting open displays with doors or purchasing closed displays.
Background We aim to assess the nutritional quality of alfalfa in saline-alkali and the main fermenting microorganisms acting on alfalfa in saline-alkali soils.
Results In this study, We tested the nutrient composition and microbial community of Zhongmu No. 3 (salt-tolerant) alfalfa, including the nutritional fermentation quality and microbial diversity analysis of alfalfa before and after ensiling (30 days and 60 days). Then we got closely genus that related to saline-alkali soils.The validity of the microbiological data was confirmed by alpha diversity analysis. From the Microbial network, we obtained the difference of the saline-type mantle type.
Conclusions we found that the silage quality of Saline-alkali alfalfa can be ensured by anaerobic fermentation with addition. The LABs that play a major role in the saline alkaline alfalfa silage are Lactobacillus, lactococcus and enterococcus.
To reveal the reconstitution mechanism of exogenous microbiota and their contributions to fermentation quality during the early stage of alfalfa ensiling. The chopped alfalfa was treated with the following: distilled water (A1); napier grass microbiota (A1N); γ-ray radiation + distilled water (A0); γ-ray radiation + napier grass microbiota (A0N). Inoculating napier grass microbiota to non-irradiated alfalfa decreased the LA concentration, while enhanced the LA production of irradiated alfalfa during the 7 d of ensiling. Inoculating napier grass microbiota increased AA and ammonia-N contents and enhanced the decline of WSC for both non-irradiated and irradiated alfalfa silages. Enterococcus and Pediococcus dominated A1 silage. Leuconostocs and Lactobacillus constituted the majority of bacterial community in A0N, Lactobacillus rapidly became the predominated genera, while Lactobacillus, Leuconostocs, Enterococcus, and Pediococcus constituted the majority of bacterial community in A1N. Thus forage microbiota transplantation may be a potential practice to improve fermentation quality of less readily fermentable forages.
The aim of this work was to evaluate effects of different gas concentrations (O2 and CO2) on conservation of minimally processed eggplants. The eggplants were sanitized, processed and packed in nylon + transparent polyethylene. The vegetables were submitted to modified atmospheres (T1= atmospheric air; T2= vacuum; T3= 4% O2 and 5% CO2; T4= 4% O2 and 6% CO2; T5= 4% O2 and 7% CO2; T6= 4% O2 and 8% CO2). The minimally processed eggplants were kept at 5±1°C and 90±1% RH, for 10 days. After 0, 2, 4, 6, 8 and 10 days of storage, fresh weight loss, respiratory rate, color, soluble solids (SS), titratable acidity (TA), pH, SS/TA ratio, visual analysis and purchase intent were determined. We used completely randomized experimental design, in a factorial scheme 6x6 (atmosphere x days of conservation). The atmosphere with higher CO2 concentration (8%) reduced the respiratory rate more intensely. The minimally processed eggplant maintained at 4% O2 + 6% CO2 obtained better grades on the visual analysis and purchase intention, with 10-day storage period. The vacuum was not recommended to keep minimally processed eggplant refrigerated under the studied conditions.
The quality and safety of minimally processed fruits and vegetables is determined by two different types of processes: (1) physiological processes such as respiration, ethylene production, enzymatic browning, and transpiration and (2) microbial processes. These processes can be retarded by using the optimal packaging design, defined as EMAP (equilibrium modified atmosphere packaging). The performance of EMAP is however highly influenced by the accuracy of the respiration rate assessment and by the initial microbial load on the fresh produce. Once the respiration rate has been assessed, the optimal packaging concept can be designed based on the necessary permeability. This permeability is determined by the polymeric material itself, but can be altered by using orientation, porous structures, or microperforations. The choice of the packaging concept will also be influenced by the filling system.
The ready-to-eat produce market has grown rapidly because of the health benefits and convenience associated with these products. Onion is widely used as an ingredient in an extensive range of recipes from breakfast to dinner and in nearly every ethnic cuisine. However, cutting/chopping of onion is a nuisance to many consumers due to the lachrymatory properties of the volatiles generated that bring tears to eyes and leave a distinct odor on hands. As a result, there is now an increasing demand for fresh-cut, value-added, and ready-to-eat onion in households, as well as large-scale uses in retail, food service, and various food industries, mainly due to the end-use convenience. Despite these benefits, fresh-cut onion products present considerable challenges due to tissue damage, resulting in chemical and physiological reactions that limit product shelf-life. Intensive discoloration, microbial growth, softening, and off-odor are the typical deteriorations that need to be controlled through the application of suitable preservation methods. This article reviews the literature related to the fresh-cut onion, focusing on its constituents, nutritional and health benefits, production methods, quality changes throughout storage, and technologies available to increase product shelf-life.
Practical application:
FTIR spectroscopy provided a method potentially transferable to the food industry when associated with the multivariate analysis. The robust 21 PLS models defined in this work provided reliable tools for the rapid monitoring of juices' authenticity and/or deterioration. In this regard, FTIR associated to multivariate analysis enabled the determination of different sugars in a single measurement without the need of pure sugars as standards. This experimental simplicity supports the use of FTIR at the production line, and also contributes to save time in determining carbohydrates' composition and stability, in an environmentally friendly way.
Vegetable products have dramatically increased in India during the past few decades. It is also estimated that about 20 % vegetables produced is lost each year due to spoilage by insects and microorganisms. This present research work addressed the characteristics of spoilage microorganisms associated with vegetable categories including spoilage mechanisms, spoilage defects, prevention and control of spoilage and methods for detecting spoilage microorganisms. In this present study, an attempt was made to isolate and identify the bacteria and fungi from the spoiled vegetables like brinjal, bitterguard, onion, carrot, tomato, potato, beetroot and radish. The vegetable samples were Available online at www.lsrj.in 1 collected from Chidambaram vegetable market area, Tamil Nadu. Isolation was carried out using Pour plate technique. The bacterial isolates were identified as Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Vibrio cholerae and Salmonella typhi by using preliminary tests, plating on selective media and biochemical tests. The fungal isolates were identified as Aspergillus niger, Penicillium expansum and Mucor racemosus based on Lactophenol cotton blue staining and plating on Sabouraud's dextrose agar.
The application of low oxygen through modified atmosphere packaging (MAP) is a technique used successfully to preserve the visual quality of lettuce and some other commodities. The expansion of use of low O2 via MAP to preserve quality of most commodities is limited by technical difficulties achieving target O2 concentrations, adverse physiological responses to low O2, and lack of beneficial responses to low O2. Low O2 often is not used simply because the physiological responses governed by the gas are not limiting quality maintenance. For instance, shelf life may be governed by decay susceptibility, which is largely unaffected by low O2 and may actually be exacerbated by the conditions encountered in hermetically sealed packages. Physiological processes influenced by low O2 and limit storability are discussed. The interdependence of O2 concentration, O2 uptake by the product, and temperature are discussed relative to requirements for packaging films.
The tolerances of horticultural commodities to CO2 are outlined, as are also the associated biochemical and physiological aspects of differences in tolerance between and within commodity types. These tolerances are related to responses to the use of modified atmosphere packaging (MAP) during storage. Commodities vary widely in their responses to elevated CO2, and low tolerance to the gas limits its use to maintain quality in some cases. Standard recommendations are generally those established to extend the storage period of any given commodity as long as possible, and safe atmospheres may differ substantially for shorter term exposures used in MAP. Use of MAP for storage of minimally processed products represents an important example of this, as storage periods and quality attributes required for commercial marketing of cut products can be very different from those of the whole product. Factors such as cultivar and postharvest treatment before imposing high CO2 can influence responses of commodities to CO2, but are rarely considered in cultivar selection or in commercial application. A better understanding of the physiology and biochemistry of commodity responses to CO2 is required for increased use of MAP.
The quality of four types of packaged salad products (retail and foodservice Garden salad, Caesar salad, and European salad)
manufactured by five major processors and stored at 5 °C for 20 days was assessed. The O2 and CO2 concentrations in the bags were 0.2–1.5% and 5–30%, respectively. Overall visual quality scores were generally at or above
the minimum acceptable value for salability at the “Best if Used by Date” (12–16 days after processing). Product sensory attributes
(visual, flavor and textural properties) determined by a trained judge and a sensory panel significantly correlated for most
of the parameters. Off-odors developed in the packages and their scores significantly correlated with ethanol and acetaldehyde
concentrations in the lettuce tissue. Sugar content decreased 12% (iceberg) to 20% (romaine) from days 0 to 15. Total aerobic
microbial load increased by an average of 2.5–3 log units over 20 days.
It is likely that from the time of the Roman Empire and perhaps before, people involved in the storage of plant material as food recognized that atmospheric modification can provide some benefit in improving storability. However, active, commercial modification of the atmosphere for the preservation of fresh fruit and vegetables dates to the early part of this century. Early successes with apple fruit has lead to the attempt to apply modified atmospheres to a wide range of commodities. Responses to atmospheric modification are found to vary dramatically among plant species, organ type and developmental stage and include both unwanted and beneficial physiological responses. Desirable responses include a reduction in respiration, a reduction in oxidative tissue damage or discoloration, a reduction in the rate of chlorophyll degradation and a reduction in ethylene sensitivity with the concomitant reduction in the rate of ripening and other ethylene-mediated phenomena. Undesirable responses have included the induction of fermentation, the development of disagreeable flavors, a reduction in aroma biosynthesis, the induction of tissue injury and an alteration in the makeup of microbial fauna. The physiological bases for some of these responses to elevated CO2 and reduced O2 are discussed.
Lactic acid bacteria (LAB) associated with gaseous spoilage of modified-atmosphere-packaged, raw, tomato-marinated broiler
meat strips were identified on the basis of a restriction fragment length polymorphism (RFLP) (ribotyping) database containing
DNAs coding for 16S and 23S rRNAs (rDNAs). A mixed LAB population dominated by aLeuconostoc species resembling Leuconostoc gelidum caused the spoilage of the product. Lactobacillus sakei, Lactobacillus curvatus, and a gram-positive rod phenotypically similar to heterofermentativeLactobacillus species were the other main organisms detected. An increase in pH together with the extreme bulging of packages suggested
a rare LAB spoilage type called “protein swell.” This spoilage is characterized by excessive production of gas due to amino
acid decarboxylation, and the rise in pH is attributed to the subsequent deamination of amino acids. Protein swell has not
previously been associated with any kind of meat product. A polyphasic approach, including classical phenotyping, whole-cell
protein electrophoresis, 16 and 23S rDNA RFLP, 16S rDNA sequence analysis, and DNA-DNA reassociation analysis, was used for
the identification of the dominantLeuconostoc species. In addition to the RFLP analysis, phenotyping, whole-cell protein analysis, and 16S rDNA sequence homology indicated
that L. gelidum was most similar to the spoilage-associated species. The two spoilage strains studied possessed 98.8 and 99.0% 16S rDNA sequence
homology with the L. gelidum type strain. DNA-DNA reassociation, however, clearly distinguished the two species. The same strains showed only 22 and 34%
hybridization with the L. gelidum type strain. These results warrant a separate species status, and we propose the nameLeuconostoc gasicomitatum sp. nov. for this spoilage-associated Leuconostoc species.
Bacteria, yeasts, and molds isolated from partially processed iceberg lettuce were taxonomically classified. The majority of bacterial isolates were gram-negative rods. Pseudomonas, Erwinia, and Serratia species were commonly found. Yeasts most frequently isolated from lettuce included members of the genera Candida, Cryptococcus, Pichia, Torulaspora, and Trichosporon. Comparatively few molds were isolated; members of the genera Rhizopus, Cladosporium, Phoma, Aspergillus, and Penicillium were identified.
The production of toxin by a 10-strain mixture of proteolytic Clostridium botulinum in fresh produce packaged in polyethylene films with different oxygen permeability was determined. Broccoli florets, shredded carrots, and green beans inoculated with approximately 10(2) C. botulinum spores per g were placed in bags (1.4 kg per bag) composed of four films with different oxygen transmission rates (OTRs). Broccoli was packaged in bags with OTRs of 3 (7,000 cm3/m2/24 h) and 4 (16,000 cm3/m2/24 h), and green beans were packaged in bags with OTRs of 2 (6,000 cm3/m2/24 h) and 4. Broccoli and green beans in bags were compressed and heat-sealed. Shredded carrots were packaged in bags with OTRs of 1 (3,000 cm3/m2/24 h) and 3 and vacuum-sealed. Produce was stored at 4, 13, and 21 degrees C for up to 27 (broccoli) or 28 (carrots and green bean) days and analyzed periodically. At each sampling time, gas composition within the bags, pH of the produce microbial population (total aerobic and anaerobic microorganisms, lactic acid bacteria, psychrotrophic bacteria, yeasts, and molds), and the presence or absence of botulinal toxin were determined. Packaging material affected the quality of vegetables, especially broccoli stored at 4 and 13 degrees C. For example, broccoli was scored as "good" after 22 days at 4 degrees C when it was packaged in film with higher gas permeability (OTR of 4), whereas broccoli appeared to be in "poor" condition when packaged in film with lower gas permeability (OTR of 3). With the exception of lactic acid bacteria, packaging material did not noticeably influence the growth of microorganisms. Lactic acid bacteria grew better in broccoli packaged in bags with an OTR of 3 than in those with an OTR of 4 at all temperatures. Botulinal toxin was detected in broccoli packaged in bags with an OTR of 3 and stored at 13 degrees C for 21 days and in those with an OTR of 4 and 3 and stored at 21 degrees C for 10 days. All toxic samples were visibly spoiled. Toxin was not detected in produce packaged under any other test conditions.
Storage experiments were conducted to follow the behavior of pathogens on fresh-cut vegetables (trimmed brussels sprouts, grated carrots, shredded iceberg lettuce, and shredded chicory endives) packaged under an equilibrium-modified atmosphere (EMA) (2 to 3% O2, 2 to 3% CO2, and 94 to 96% N2) and stored at 7 degrees C. As a comparison, fresh-cut vegetables were also packaged in a perforated high-barrier film (air conditions) and stored at 7 degrees C. In a first step, the shelf life of the vegetables in the two kinds of packages was determined by evaluating the microbiological quality as well as the sensorial quality (appearance, taste, and odor). In general, sensorial properties were faster in limiting the shelf life than microbiological criteria. The shelf life of the vegetables stored under an EMA was extended by 50% or more, compared with the air-stored vegetables. In a second storage experiment, the four fresh-cut vegetables were inoculated with a cocktail of psychrotrophic pathogens (Listeria monocytogenes, Aeromonas caviae [HG4]) and A. bestiarum (HG2) before packaging under an EMA and air at 7 degrees C. The inoculated pathogens were more influenced by the type of vegetable than by the type of atmosphere. No growth was detected on the brussels sprouts or on carrots (L. monocytogenes). Aeromonas spp. had a higher growth rate than L. monocytogenes on the shredded chicory endives and shredded iceberg lettuce at 7 degrees C.
Lactic acid bacteria (LAB) associated with gaseous spoilage of modified-atmosphere-packaged, raw, tomato-marinated broiler meat strips were identified on the basis of a restriction fragment length polymorphism (RFLP) (ribotyping) database containing DNAs coding for 16S and 23S rRNAs (rDNAs). A mixed LAB population dominated by a Leuconostoc species resembling Leuconostoc gelidum caused the spoilage of the product. Lactobacillus sakei, Lactobacillus curvatus, and a gram-positive rod phenotypically similar to heterofermentative Lactobacillus species were the other main organisms detected. An increase in pH together with the extreme bulging of packages suggested a rare LAB spoilage type called "protein swell." This spoilage is characterized by excessive production of gas due to amino acid decarboxylation, and the rise in pH is attributed to the subsequent deamination of amino acids. Protein swell has not previously been associated with any kind of meat product. A polyphasic approach, including classical phenotyping, whole-cell protein electrophoresis, 16 and 23S rDNA RFLP, 16S rDNA sequence analysis, and DNA-DNA reassociation analysis, was used for the identification of the dominant Leuconostoc species. In addition to the RFLP analysis, phenotyping, whole-cell protein analysis, and 16S rDNA sequence homology indicated that L. gelidum was most similar to the spoilage-associated species. The two spoilage strains studied possessed 98.8 and 99.0% 16S rDNA sequence homology with the L. gelidum type strain. DNA-DNA reassociation, however, clearly distinguished the two species. The same strains showed only 22 and 34% hybridization with the L. gelidum type strain. These results warrant a separate species status, and we propose the name Leuconostoc gasicomitatum sp. nov. for this spoilage-associated Leuconostoc species.
Modified atmosphere packaging (MAP) is a technology that is currently used for most packaged salads and fresh-cut vegetables, and to a lesser extent, fresh-cut fruit such as cantaloupe (Cucumis melo L.), pineapple [Ananas comosus L. (Merr.)], and apple (Malus x domestica Borkh.). In addition, about 750 million lb (340,200 Mg) of strawberries (Fragaria x ananassa Duch.), raspberries (Rubus idaeus L.) and sweet cherries (Prunus avium L.) are distributed in MAP annually. The fresh produce packaging industry has developed new trims to respond to increased produce consumption and changes in the use of trim packaging within different produce marketing segments. The produce film industry sold 60 million lb (27,200 Mg) of film in 1994, and in 2000 it is forecasted to sell 110 million lb (49,900 Mg), an increase of 83%. The distribution of film usage has also changed since 1994 when trim consumption patterns were as follows: 20% [12 million lb (5,400 Mg)] retail, 15% [9 million lb (4,100 Mg)] warehouse clubstores, and 65% [39 million lb (17,700 Mg)] food service. In 2000 it is projected that consumption patterns will be as follows: 25% [27.5 million lb (12,500 Mg)] retail, 20% [22 million lb (10,000 Mg)] warehouse clubstores, and 55% [60.5 million lb (27,400 Mg)] food service. These changes represent a 10% shift in trim market segment usage patterns away from food service applications to an increase of 5% for each of the retail and warehouse clubstore segments.
Lactobacillus brevis is a microaerophilic, obligately heterofermentative lactic acid bacterium isolated from many different environments. Lactobacillus brevis is involved in the production of a wide variety of fermented products worldwide. However, in some circumstances it can cause spoilage of various foods and beverages. Lactobacillus brevis is one of the most undesirable beer-spoilage microorganisms. Several potential health benefits have been attributed to the consumption of products containing probiotic strains of this specie. This chapter considers the general characteristics of the organism, detection and enumeration methods, and its importance for the food industry and the consumer.
To obtain more insight into the specific impact of modified gas conditions on the composition of microflora of minimally processed vegetables, the prevalent bacteria on mungbean sprouts and cut chicory endive were determined during storage under controlled atmospheric (CA) conditions at 8°C. Enumeration of the total mesophilic counts, Enterobacteriaceae,Pseudomonasspecies, and lactic acid bacteria indicated that Enterobacteriaceae andPseudomonasspecies constituted the major populations found on these products before and after CA storage. Identification of the predominant species within these populations revealed that on fresh and CA-stored mungbean sprouts,Enterobacter cloacae, Pantoea agglomerans, Pseudomonas fluorescens, Ps. viridilividaandPs. corrugatawere the prevalent species. On chicory endive,Rahnella aquatilisand severalPseudomonasspecies were found on the fresh product, while after CA storage,Escherichia vulnerisandPs. fluorescenswere the main species. Growth of the predominant epiphytes was subsequently quantified in pure culture, using an agar model system at 8°C under 1.5 or 21% O2with 0, 5, 20, or 50% CO2. In general, these CA conditions did not strongly influence maximum population densities and lag times were not detected. For each of the strains, however, maximum specific growth rates were reduced at increased CO2concentrations, independent of the 02concentration applied. This effect was more pronounced forPseudomonasspecies than forEnterobacteriaceae. Notably, the agar model study showed that individual species ofEnterobacteriaceaeorPseudomonasresponded similarly to the specific CA conditions applied. This did not correlate with the shift in predominant species observed on chicory endive. Our data underline the complexity of the ecological conditions to which micro-organisms on vegetables are subjected during storage under modified gas conditions.
Bacteria responsible for decay of precut celery (Apium graveolens) appear to be residents on the plants at harvest. Bacterial genera isolated from equipment in a fresh celery packinghouse were similar to those found on plants sampled at the packinghouse entrance. Population densities and array of genera were highest on unwashed plants, whereas certain genera were no longer detected on the washed plants. Fluorescent Pseudomonas spp. predominated, but strains of Pantoea agglomerans (=Erwinia herbicola), Enterobacter agglomerans, Aeromonas, Arthrobacter, and Aureobacterium were frequently isolated. Members of the coliform group such as Citrobacter, Klebsiella, and Escherichia were rare.
Modified atmosphere packaging is becoming increasingly common. It has been claimed that the technique enables significant shelf-life extension but in so doing presents an increased public health risk. This paper reviews the literature relating to the scientific basis of these claims. It demonstrates that shelf-life, sensory quality and safety of packaged products may be optimised only by harmonising a complex relationship between product and process.
The effect of initial head spaces of air, 4.9% CO2/2.1% O2/93% N2 and 5% CO2/95% N2 on the microbial flora of shredded carrots was studied at 4 and 10°C. The microbial flora of shredded carrots comprised lactic acid bacteria, pseudomonads and yeasts. Lactic acid bacteria were the predominant organisms in all samples. The pH dropped during the storage of carrots and this was more pronounced at 10°C. The concentration of different organic acids such as lactic, acetic, tartaric, citric and succinic increased in all samples stored under modified atmosphere packaging conditions at both temperatures. The spoilage of carrots stored under 5% CO2/95% N2 was delayed, as indicated by the changes in their texture, colour and odour, compared with those samples stored under air or 4.9% CO2/2.1% O2/93% N2.
An improved method for purification of pectate lyases (PLI and PLII) from culture fluids of Pseudomonas fluorescens CY091 and Ps. viridiflava PJ-08-6 by using a phosphocellulose cation exchanger was described. Analysis of purified PLI and PLII by sodium dodecyl sulphate-polyacrylamide and isoelectric focusing gel electrophoresis revealed that both enzymes had been purified to near homogeneity. Optimal Ca2+ concentration required for PLI and PLII activity was determined to be 0·5 mmol l−1. The Ca2+ requirement could not be replaced by other metal cations such as Mg2+, Cu2+, Zn2+, Fe3+ and Co2+. Optimal pH for activity was determined to be between 8·5 and 9·0. The Km values for sodium polygalacturonate were 1·28 and 1·11 mg ml−1 for PLI and PLII, respectively. Both PLI and PLII were stable at low temperatures (25°C or below) for at least 1 month. However, at 37°C, the activity decreased 50% in 36 h. Optimal temperatures for activity were estimated to be 46° and 52°C for PLI and PLII, respectively. Thermal stability of both enzymes at elevated temperatures (48°C or higher) increased when CaCl2 or a positively charged molecule such as polylysine was present, but decreased when polygalacturonate or a negatively charged molecule such as heparin was present. PLI and PLII exhibit differential degrees of sensitivity to group-specific inhibitors, including iodoacetic acid and diethylpyrocarbonate. This result suggests that both sulphydryl and imidazole groups are important for the catalytic function of PLI and PLII.
Numerous factors affect the storage stability of shredded Iceberg lettuce, with temperature being most important. Pouches of shredded lettuce stored at 2°C retained a marketable quality 2.5 times longer than those held at 10°C. Also, if the product was sealed in a gas impermeable container it lasted longer. In addition, a sharp blade exercising a slicing action was superior to either a sharp blade chopping or a dull blade slicing or chopping. Smaller shred size reduced storage life, as did the presence of any free moisture or cellular fluids on the lettuce surface. The higher the microbial load the shorter the storage life. Of the chemical dips tested none increased storage life significantly. Physical damaging of the shredded lettuce was detrimental to its storage stability.
ABSTRACTA decay of fresh-cut celery (Apium graveolens) segments stored at < 5°C in sealed film bags began with a water soaking of the cut surfaces. Slimy moisture accumulated inside the bags. The segments water soaked completely, softened, discolored and sometimes disintegrated. Total aerobic bacterial populations isolated from decayed segments ranged from log10 7.0–7.7 CFU/g tissue weight. The predominant bacteria, identified by fatty acid analysis as Pseudomonas fluorescens and P. marginalis, caused water soaking, soft rot, and discoloration in freshly inoculated celery tissues stored at 5 or 25°C. Leuconostoc mesenteroides was also isolated and may have been responsible for slime production.
Spoilage of ready-to-use grated raw carrots packaged in polymeric films and stored at 10°C was investigated for involvement of yeasts. Cryptococcus albidus was only isolated during the first 3 days of storage, increasing to levels of 105–106g-1. Candida lambica was more commonly isolated after 3–7 days of storage, and reached 107–108g-1 after 12 days. Candida sake was present throughout storage, increasing from 105–106 after 3 days to 107–108 after 12 days. In some samples, Candida parapsilosis and Candida tropicalis were also isolated at levels similars to C. sake. All the yeasts isolated at the end of storage were fermentative species and their metabolism was characterized with a Warburg apparatus. Neither the number of yeasts nor the composition of the yeast flora were related to the deterioration of the product. Although Candida lambica inoculated on grated carrots caused spoilage after 12 days at 10°C, the high O2 permeable film was most effective in reducing exudate.
Cultivars of shredded iceberg lettuce (Lactuca sativu L.) ‘Saladin’, ‘Santis’, ‘Telda’ and ‘Roxette’ responded in a parallel way to four modified atmosphere (MA) packaging treatments. Moderate vacuum packaging (mvp) in 80 μm polyethylene (PE) inhibited enzymatic browning over 10-day storage at 5°C. When lettuce was packaged in 80% O2, 20% CO2 (80/20), more browning occured in SL3-bags (59 μm multilayer coextruded film) than in PE-bags. Polyphenol oxidase activity declined during storage in all 4 atmospheres, with lowest activity in PE-80/20. Endogenous ascorbic acid (AA) did not act as an efficient antioxidant in delaying browning. Total carbohydrate content (TC) declined slightly during storage. Tristimulus color measurements correlated highly with visual ratings.
Storage of partially processed lettuce resulted in an increase in microbial population, pH, and change in package atmosphere composition (increasing CO2 and decreasing O2). Microbial populations varied in size with variations in processing and packaging. Typical initial log10 counts per g were: bacteria 3.4–5.1, yeasts 2.5–3.2; molds were infrequent. Commercial packaging inhibited bacterial growth and retarded browning. Although Gram-negative bacteria were numerically dominant, a large yeast population was also found. Species in the genera Pseudomonas, Erwinia, and Serratia were the most frequently isolated bacteria. Cryptococcus, Pichia, Torulaspora and Trichosporon spp. were the most common yeasts.
Storage temperature is never constant in the distribution chain of fresh foods. Due to the temperature dependence of respiration of fresh produce and O2permeability of a packaging film, fluctuating temperatures result in changes of the internal O2and CO2concentration of Equilibrium Modified Atmosphere (EMA) packaged fresh produce.Therefore, the design of EMA packages was improved by adding mathematical models describing the effect of temperature, O2and CO2levels on produce respiration. The influence of temperature on respiration was described by an Arrhenius type of equation while the influence of O2and CO2on respiration was modelled by a Michaelis–Menten kinetic for 10 types of fresh-cut produce. Compared to unprocessed vegetables a higher temperature dependence of cut/shredded produce was observed. An integrated mathematical model characterized the effect of produce type, produce weight, temperature, O2and CO2dependence of produce respiration, film type, package area and temperature dependence of film permeability for O2in order to predict the internal O2concentration of an EMA package which was designed for equilibrium concentration of 3 mL/100 mL O2at 7°C. The model was validated by packaging 10 types of fresh-cut vegetables and comparing equilibrium O2levels with those predicted at six different temperatures between 2 and 15°C.
A systematic approach is validated for designing equilibrium modified atmosphere (EMA) packages (1–5 mL/100 mL O2, 3–10 mL/100 mL CO2, balance N2) for fresh-cut produce (trimmed Brussels sprouts, shredded spinach, shredded chicory endives, shredded iceberg lettuce, grated carrots, complete heads of iceberg lettuce and a mixture of red, green and yellow bell peppers). The respiration rate is calculated by two mathematical methods based on measurements conducted at the same conditions (temperature, relative humidity, gas composition) as those created in the EMA packages. When the respiration rate, the fill weight and the package dimensions are known, the required transmission rate for O2and CO2of the packaging film is determined for each commodity based on steady state equations. New packaging films with high permeability for O2and CO2were tested in these experiments. A validation of the designed packages is necessary to complete this systematic approach and to determine the shelf-life of the EMA packaged fresh-cut produce.
A solid surface model system was developed to study the effect of gas atmosphere composition on the growth of Aeromonas hydrophila, Yersinia enterocolitica, Listeria monocytogenes, and a cold tolerant strain of Bacillus cereus. The organisms were incubated on an agar surface at 8°C under either 1·5 or 21% O2, combined with 0, 5, 20 or 50% CO2. The remainder of each atmosphere was made up to 100% with N2. Growth was evaluated on the basis of three parameters, namely maximum specific growth rate, maximum population density and lag time. These parameters were derived from growth data by fitting with a modified Gompertz equation. In all instances the maximum specific growth rate decreased significantly with increasing CO2 concentration. A strong reduction in the maximum population density was noted only for B. cereus at the highest level of CO2. The O2 concentrations tested did not significantly affect maximum specific growth rates nor maximum population densities in any case. Prolonged lag times were observed only for Y. enterocolitica under 50% CO2/21% O2/29% N2.The results indicate that the model system may be a suitable means of estimating the growth of bacteria on minimally processed produce, packaged under modified atmospheres. Extrapolation of our results to modified atmosphere packaged (MAP) fruits and vegetables using typical O2 concentrations of 1–5% and CO2 concentrations of 5–10%, suggest that growth of the above pathogens may occur at 8°C, thereby imposing a safety hazard for these products.
Heads of lettuce (Lactuca sativaL., cv. ‘Salinas’) were individually wrapped or sealed in nonoriented perforated (22 μm thickness) or unperforated (25 or 50 μm thickness) new polypropylene (PP) films, and stored for 2 weeks at 2 °C plus 2·5 d at 12 °C. Vacuum cooling and/or active modification of the atmosphere within the package by flushing a gas mixture were applied. Quality of lettuce by scoring wilting, physiological disorders, bacterial decay and overall visual quality was determined. In naked heads stored in air and in lettuce wrapped in perforated PP, russet spotting and pink rib, the main disorders of lettuce during postharvest, developed. However, in all treatments with sealed PP bags, these disorders practically did not appear. Heart leaf injury and brown stain developed on lettuce sealed in PP bags, particularly after transfer to higher temperature. Pink rib and heart leaf injury mainly appeared in vacuum cooled lettuce. The reason for this susceptibility, that has not been previously reported, is unknown and additional research is needed to identify the factors involved. Low O2was related with high quality score. The best results were obtained in vacuum cooled lettuce packed in PP bags with initial 21·6 g/L O2and 0 g/L CO2atmosphere.
The application of High Oxygen Atmospheres (HOA) (i.e. >70% O2) for packaging ready-to-eat vegetables was evaluated as an alternative technique for low O2 Equilibrium Modified Atmosphere (EMA) packaging (3% O2–5% CO2–balance N2) for respiring products. Comparative experiments between both techniques were performed in-vitro and in-vivo. Typical spoilage causing microorganisms (Pseudomonas fluorescens, Candida lambica), the moulds Botrytis cinerea, Aspergillus flavus and the opportunistic psychrotrophic human pathogenic microorganism associated with refrigerated minimally processed vegetables, Aeromonas caviae (HG4), showed a retarded growth during the conducted in-vitro studies at 4 °C in 70%, 80% and 95% O2 as examples of HOA compared to the in-vitro experiments in 5% O2 (as example of EMA packaging) and the effect was more pronounced in 95% O2. The effect of the high O2-concentrations on the human pathogen Listeria monocytogenes resulted in an extended lag phase (95% O2). The plant pathogen Erwinia carotovora was increasingly stimulated by increasing high O2-concentrations. During a storage experiment of three types of ready-to-eat vegetables (mushroom slices, grated celeriac and shredded chicory endive), which are sensitive to enzymatic browning and microbial spoilage, the effect of EMA and HOA (95% O2–5% N2) on their quality and shelf life was compared. High O2 atmospheres were found to be particularly effective in inhibiting enzymatic browning of the tested vegetables. Also, the microbial quality was better as a reduction in yeast growth was observed. The HOA can be applied as an alternative for low O2 modified atmospheres for some specific types of ready-to-eat vegetables, sensitive to enzymatic browning and spoilage by yeasts.
The respiratory rate of fruits and vegetables can be used as an indicator for designing storage conditions to maximize the longevity of these commodities. One postharvest technique that has been used to prolong the storage life of some of these commodities is the use of a controlled atmosphere. The modulation of respiratory metabolism of such commodities held in controlled atmospheres containing reduced oxygen and/or elevated carbon dioxide levels has been thought of as the primary reason for the beneficial effects on the commodities. However, the mechanism by which elevated carbon dioxide influences the regulation of respiratory metabolism is still obscure and several hypotheses have been proposed for its mode(s) of action. The regulation may be directed towards the glycolytic pathway, the fermentative metabolism, the tricarboxylic acid cycle or the electron transport system, presumably through its influence on the synthesis, degradation, inactivation and/or activation of the respective enzymes. It may also be through the antagonistic effects of carbon dioxide on ethylene action as well as its influence on secondary metabolism through an alteration in cell pH. This article discusses the recent developments on the biochemical and physiological fronts as well as the possible mode(s) of action of elevated carbon dioxide in the regulation of respiratory metabolism in fruits and vegetables.
Fresh-cut fruits and vegetables are highly perishable due to damaged and exposed tissues and lack of protective skin. Disorders arising from processing can be minimized by the use of sharp cutting tools, enzymatic browning inhibitors, modified atmospheres and low temperatures. High quality can be maintained by selecting produce at proper maturity and controlling deterioration with low temperatures and modified atmospheres. By recognizing and controlling factors that have a deteriorative effect on quality, good quality fresh-cut product with sufficient shelf-life can be attained.
The identifiability properties of the Baranyi model for bacterial growth were investigated, both structurally and applied to real-life data. Using the Taylor-series approach, it was formally proven that the model is structurally identifiable, i.e. it is now ascertained that it is certainly possible to give unique values to all parameters of the model, provided the bacterial growth data are of sufficiently good quality. The model also has acceptable practical identifiability properties in the presence of realistic data, which means that the confidence intervals on the parameter values are reasonable. However, there was a relatively high correlation between the maximum specific growth rate μmaxand the suitability indicator h0. An optimal experimental design to improve parameter estimation uncertainty was worked out, using the sampling times of the microbial growth curve as experimental degree of freedom. Using a D-optimal design criterion, it could be shown that the optimal sampling times were concentrated in four time periods (initial, start and end of exponential growth, end of experiment), each providing maximum information on a particular parameter. Because the optimal experimental design requires a priori estimates of the parameters, the propagation of the parameter uncertainty into the experimental design was assessed with a Monte Carlo simulation. In this way, 95% confidence intervals could be established around the optimal sampling times to be used in the optimal experiment. Based on these intervals, a design was proposed and experimentally validated. The error on the parameter estimates was more than halved, their correlation diminished and the nonlinearity of the result improved.
Oxygen consumption as influenced by carbon dioxideHigh carbon dioxide (CO 2 ) concentrations can reduce the oxygen (O 2 ) consumption rate of a number of fruits and vegetables. This reduction can be modelled by incorporating an inhibition term in an Michaelis-Menten type of model, describing the overall respiration process as a single enzyme reaction. Four types of inhibition can be distinguished: 1. the competitive type, 2. the uncompetitive type, 3. a combination of both previous types and 4. the non-competitive type (after Chang, 1981). Using the inhibition terms a good estimation of O 2 consumption could be obtained. This supports the use of Michaelis- Menten kinetics for modelling O 2 consumption.Depending on the product the statistical analysis gave good results for the competitive and the uncompetitive type of inhibition. Based on gas exchange data only, no distinction between the competitive and uncompetitive type of inhibition could be made. The data suggest the simultaneous existence of both types of inhibition. However, for reasons of simplicity the non-competitive type of inhibition is preferred, giving good results for all the products tested. This non-competitive inhibition term, evaluated in chapter 2, is used in other chapters whenever an influence of CO 2 on respiration was found.Oxidative and fermentative carbon dioxide productionBecause the main metabolic sources for CO 2 emission by higher plants are respiration and fermentation, both processes have to be incorporated in a model describing total CO 2 production. For this purpose one existing model (Peppelenbos et al., 1993) was adjusted and, based on different theories, two models were developed. The adjusted model used O 2 as an inhibitor of fermentative CO 2 production, whereas the two new models used the ATP production rate, representing ATP concentration. The difference between the latter two models is that in the first one ATP production is calculated by using only oxidative processes, while in the second one ATP production is calculated by a combination of oxidative and fermentative processes. All models allow for increased CO 2 production at low O 2 concentrations, as is often found for several products. The best performance was found for the adjusted model and the new one which used oxidative ATP. The results do not clarify whether increased fermentation rates can be attributed to decreased O 2 levels or decreased energy fluxes. The approach used, however, enables the calculation of CO 2 production rates of different types of commodities stored under various gas conditions. This facilitates a better prediction of CO 2 conditions inside storage rooms and MA packages.Alcoholic fermentation as influenced by carbon dioxideNot only respiration can be influenced by high CO 2 concentrations. In several products this influence is also found on fermentation. This influence was incorporated in the CO 2 production model based on the inhibition of alcoholic fermentation by O 2 (the'adjusted' model). Gas exchange rates of mungbean sprouts under various O 2 and CO 2 concentrations were used to validate the model. With the modification applied, CO 2 production rates were described better. Although CO 2 production at low O 2 concentrations was reduced by high CO 2 concentrations, the data showed no influence on ethanol and acetaldehyde levels.The data obtained indicate large differences between gas exchange rates of different batches of mungbean sprouts. It is suggested that microbial metabolism attributes substantially to total CO 2 production rates found, and might explain these differences.The simultaneous measurement of gas exchange and diffusion resistanceA method was developed to measure metabolic gas exchange rates and gas diffusion resistance of apples simultaneously, under various gas conditions. For this purpose the trace gas neon was selected. After closing a flask containing an apple already kept at a specific gas condition, the neon partial pressure was brought to 110 Pa. Changes in oxygen and carbondioxide concentration in the flask were used to calculate gas exchange, and the decrease in neon concentration was used to calculate gas diffusion resistance. The calculated resistance values were compared with data obtained from literature, and estimations of O 2 and CO 2 resistance values were made. The method worked well on apples, but this will not necessarily be the case when products are measured with small internal gas volumes.Functioning of gas exchange models using internal and external concentrationsBased on gas exchange rates and diffusion resistance, internal gas concentrations of apple cultivars Golden Delicious, Elstar and Cox's Orange Pippin were calculated. Internal O 2 concentrations were 2.3 kPa lower at an external O 2 concentration of 20.7 kPa for Golden Delicious apples, and about 4.5 kPa lower at 20.1 and 20.4 external O 2 for Elstar and Cox's apples respectively. Internal CO 2 concentrations substantially exceeded normal external concentrations of 50 Pa. The Km values found for the three apple cultivars remained significantly different when internal instead of external concentrations were used. This indicates that the apple cultivars measured do not only show biophysical differences (resistance, porosity), but also differences at the biochemical level.For Golden Delicious apples no difference in model functioning was found when internal or external concentrations were used. In contrast, for Elstar and Cox's Orange Pippin apples the O 2 uptake and CO 2 production models showed better results (expressed as R 2) when fitted on external concentrations. It is argued that this might be explained by the experimental setup. For instance the internal O 2 concentration of Cox's Orange Pippin calculated at the optimal external O 2 concentration (1.2%) reached 0.01 %. A small change of 0. 1 % in an external O 2 concentration close to 1 % therefore can change the internal atmosphere from hypoxia to anoxia, which cannot be regarded as an equilibrium situation. The conclusion to be drawn is that also for experimental setups some precalculations using gas exchange rates and diffusion resistances will help to optimize the methods.Gas exchange characteristics and prediction of optimal gas conditions for CA storageThe applicability of respiratory characteristics to determine optimal O 2 concentrations for the storage of apples was tested. A comparison was made between gas exchange rates of apples directly after harvest and after a period of storage. Optimal O 2 concentrations were based on gas exchange data and gas exchange models fitted on the data, using the Anaerobic Compensation Point (ACP) and the Respiratory Quotient Breakpoint (RQB). A third to establish optimal gas concentrations way was comparing total ATP production with estimated maintenance energy requirements, revealing the Maintenance Oxygen Concentration (MOC). ATP production was calculated using gas exchange models. MOC was defined as the oxygen concentration with the minimal ATP production rate necessary for maintaining cell viability. The optimal O 2 concentrations as established by ACP, RQB and MOC differed considerably. Because ACP values differed from normally advised values, the ACP was unsuitable for a quick determination of the optimal O 2 concentration of the apples used. The RQB, however, might be suitable, but than the limit used to establish the RQB should be more than 0.5 units higher than the RQ measured in ambient air. The ACP and the RQB were decreased to lower O 2 concentrations after storage, suggesting that the optimal concentrations decrease during storage. In contrast the MOC was increased after storage, which was in agreement with data as found in the literature. Model calculations indicated the lowest optimal O 2 concentration for the second (optimal) harvest using the ACP, the RQB and the MOC. It is suggested that research on the relationship between Maintenance Energy Requirements and cell injury will clarify an important part of the changes in optimal O 2 concentrations (or the tolerance to low O 2 concentrations) during ageing or maturation of harvested plant tissues.Fermentation at high oxygen concentrationsApples were stored at various O 2 concentrations, ranging between normoxia and anoxia. Gas exchange rates and the production of acetaldehyde and ethanol was measured. A gas exchange model, which distinguishes oxidative from fermentative CO 2 production, was fitted to the data. The results indicate alcoholic fermentation to be active at all the O 2 concentrations used, and increasing in importance when O 2 concentrations are lowered. After calculating the amount of metabolites in the apple tissue from the data measured in air, a close relationship was found between model predictions of alcoholic fermentation rates and measured metabolite production in normoxia and anoxia. In hypoxia, however, the model predicted higher CO 2 production rates in comparison to the metabolites actually found. Because the model was fitted to CO 2 production data, this indicates another source or CO 2 in hypoxia than alcoholic fermentation.Conclusions
The influence of CO 2 on O 2 uptake was investigated, and the known Michaelis-Menten equation given by Chevillotte (1973) was extended with the type of inhibition adequately describing this influence. Models describing fermentative CO 2 production were developed and combined with oxidative CO 2 production, enabling the calculation of CO 2 production of various products under a range of combinations of O 2 and CO 2 . Although gas exchange of mungbean and microbial growth on it could not be distinguished, a model was developed describing the total gas exchange of mungbean and microbial growth, enabling the calculation of mungbean gas exchange in MA packages. A method was derived enabling the simultaneous measurement of metabolic gas exchange and the resistance to gas diffusion. Results of these measurements showed limitations to experimental setups using headspace techniques, and indicated that optimal O 2 concentrations are very likely limited to a specific temperature. Measurements on acetaldehyde and ethanol confirm the prediction of the models describing fermentative CO 2 production, and show that fermentation is not limited to low O 2 concentrations.Optimal gas conditions for storage of produce are not fixed values but change with temperature and, more important, also during the storage period. Using fixed gas conditions for long term storage, this could lead to problems and the loss of the stored produce. Interactive storage facilities, responding to physiology of the stored material, will help to reduce this risk. Processes that should be quantified are energy metabolism and fermentation rates. Parameters related to these processes are gas exchange rates and acetaldehyde and ethanol production. For the calculation of energy production the gas exchange models described within this thesis could be used. ATP fluxes, in combination with maintenance requirements, very likely help to understand the tolerance of plant tissues to low oxygen conditions.
Yeasts are best known for their beneficial contributions to society, and the literature abounds with discussions of their role in the fermentation of alcoholic beverages, bread, and other products. Yeasts also cause spoilage, but, with a few exceptions, this unwanted activity often goes unrecognized and underestimated as a major problem in the food and beverage industries. In some cases, there is only a fine line between what is perceived as either a spoilage or beneficial activity. This review examines the occurrence and growth of yeasts in foods and beverages with respect to their spoilage activities, the biochemistry of this spoilage, and technologies for the enumeration and identification of spoilage yeasts.
Modified atmospheres (MA), i.e., elevated concentrations of carbon dioxide and reduced levels of oxygen and ethylene, can be useful supplements to provide optimum temperature and relative humidity in maintaining the quality of fresh fruits and vegetables after harvest. MA benefits include reduced respiration, ethylene production, and sensitivity to ethylene; retarded softening and compositional changes; alleviation of certain physiological disorders; and reduced decay. Subjecting fresh produce to too low an oxygen concentration and/or to too high a carbon dioxide level can result in MA stress, which is manifested by accelerated deterioration. Packaging fresh produce in polymeric films can result in a commodity-generated MA. Atmosphere modification within such packages depends on film permeability, commodity respiration rate and gas diffusion characteristics, and initial free volume and atmospheric composition within the package. Temperature, relative humidity, and air movement around the package can influence the permeability of the film. Temperature also affects the metabolic activity of the commodity and consequently the rate of attaining the desired MA. All these factors must be considered in developing a mathematical model for selecting the most suitable film for each commodity.
Retail packs of mixed, prepared salad vegetables from two different manufacturers were stored at 7 degrees C until the end of storage-life (sell-by date plus 1 d), when the microbial flora was examined. The quality of the salads was acceptable at the end of storage life. The oxygen concentrations in packs were lower, and the carbon dioxide concentrations were higher, than those in air. High numbers of bacteria were present, with Pseudomonas spp. and Enterobacter agglomerans predominating in packs of both salads, together with lactic acid bacteria in one of the salads. Significant numbers of pectolytic bacteria including Pseudomonas spp. and Erwinia carotovora were detected. Despite the presence of high numbers of coliform bacteria, Escherichia coli was not detected in batches of one salad, and was detected in relatively low numbers in batches of the other. Yersinia spp., predominantly environmental strains of Yersinia enterocolitica, were isolated by enrichment from all samples tested; Staphylococcus aureus and enterococci were not detected.
Minimally processed fresh (MPF) fruits and vegetables are good media for growth of microorganisms. They have been involved in outbreaks because of the consumption of products contaminated by pathogens. They are also sensitive to various spoilage microorganisms such as pectinolytic bacteria, saprophytic Gram-negative bacteria, lactic acid bacteria, and yeasts. Contamination of MPF fruits and vegetables occurs at every stage of the food chain, from cultivation to processing. Polluted environments during cultivation or poor hygienic conditions in processing increase the risk of contamination with foodborne pathogens. Although MPF fruits and vegetables may harbor psychrotrophic microorganisms such as fluorescent pseudomonads or Listeria monocytogenes, good control of refrigeration temperature limits growth of spoilage and pathogenic microorganisms. Modified atmospheres are often efficient to maintain or improve visual organoleptic quality of MPF fruits and vegetables, but their effects on microorganisms are inconsistent. Chemical disinfection can partially reduce the initial bacterial contamination; irradiation seems to be more efficient. The applications of legislations and quality assurance systems to control contamination, survival, and growth of foodborne pathogens in MPF fruits and vegetables are discussed.
Use of biotechnology in pulp bleaching has attracted considerable attention and achieved interesting results in recent years. Enzymes of the hemicellulolytic type, particularly xylan-attacking enzymes, xylanases are now used commercially in the mills for pulp treatment and subsequent incorporation into bleach sequences. The aims of the enzymatic treatment depend on the actual mill conditions and may be related to environmental demands, reduction of chemical costs or maintenance or even improvement of product quality. The use of oxidative enzymes from white-rot fungi, that can directly attack lignin, is a second-generation approach, which could produce larger chemical savings than xylanase but has not yet been developed to the full scale. It is being studied in several laboratories in Canada, Japan, the U.S.A. and Europe. Certain white-rot fungi can delignify kraft pulps increasing their brightness and their responsiveness to brightening with chemicals. The fungal treatments are too slow but the enzyme manganese peroxidase and laccase can also delignify pulps and enzymatic processes are likely to be easier to optimize and apply than the fungal treatments. Development work on laccase and manganese peroxidase continues. This article presents an overview of developments in the application of hemicellulase enzymes, lignin-oxidizing enzymes and white-rot fungi in bleaching of chemical pulps. The basic enzymology involved and the present knowledge of the mechanisms of the action of enzymes as well as the practical results and advantages obtained on the laboratory and industrial scale are discussed.
Malolactic fermentation
- Bozogen
Bozogen, F., Yurdugü, S., 2000. Malolactic fermentation. In: Robin-son, R., Batt, C., Patel, P. (Eds.), Encyclopedia of Food Micro-biology, vol. 3. Academic Press, London, UK, pp. 2311 – 2316.
Lactobacillus/introduction Encyclopedia of Food Microbiology
- C Batt
Batt, C., 2000. Lactobacillus/introduction. In: Robinson, R., Batt, C., Patel, P. (Eds.), Encyclopedia of Food Microbiology. Aca-demic Press, London, UK, pp. 1134 – 1136.
Lactobacillus brevis
- P Teixeira
Teixeira, P., 2000. Lactobacillus brevis. In: Robinson, R., Batt, C., Patel, P. (Eds.), Encyclopedia of Food Microbiology, vol. 2. Academic Press, London, UK, pp. 1144 – 1151.
Criteria en praktische methoden voor de bepaling van de houdsbaarheidsdatum in de etikettering
- Debevere
Debevere, J., 1996. Criteria en praktische methoden voor de bepal-ing van de houdsbaarheidsdatum in de etikettering. In: Tem-merman, G., Cremer, C., Thyssen, M., Debevere, J. (Eds.), Etikettering, houdbaarheid en bewaring (voedingsmiddelen en recht 2). Die Keure, Brugge, Belgium, pp. 35 – 64.
Effect of preparation and storage parameters on quality retention of salad-lettuce Factors affect-ing the storage stability of shredded lettuce
- H Bolin
- C Huxsoll
Bolin, H., Huxsoll, C., 1991. Effect of preparation and storage parameters on quality retention of salad-lettuce. J. Food Sci. 56 (60 – 62), 67. Bolin, H., Stafford, A., King, A., Huxsoll, C., 1977. Factors affect-ing the storage stability of shredded lettuce. J. Food Sci. 42, 1319 – 1321.
Unit operations for fresh-cut produce Campden & Chorley-wood Food Research Association Group
- P Varoquaux
Varoquaux, P., 2001. Unit operations for fresh-cut produce. Confer-ence Proceedings of Second International Conference on Fresh-Cut Produce, 13 – 14 September 2001. Campden & Chorley-wood Food Research Association Group, Chipping Campden, UK.
Belgische voedingsmiddelentabel
- Nubel
Nubel, 1999. Belgische voedingsmiddelentabel, 3rd ed. Nubel, Brussels, Belgium, pp. 39 – 44.
Unit operations for fresh-cut produce
- Varoquaux
Minimally processing of fresh produce
- Ahvenainen