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Valorization of household food wastes to lactic acid production: A response surface methodology approach to optimize fermentation process
Abstract
Lactic acid is a valuable compound used in several industrial processes such as polymers, emulsifiers manufacturing, pharmaceutical, and cosmetic formulations. The present study aims to evaluate the potential use of food waste to produce lactic acid through fermentation, both by indigenous microbiota and by the bio-augmentation with two lactic acid bacteria, namely Lactobacillus plantarum BS17 and Lactobacillus casei BP2. Fermentation was studied both in batch and continuously fed anaerobic reactors at mesophilic conditions and a Response Surface Methodology approach was used to optimize the bioprocess performance and determine the environmental parameters (namely pH and time) that lead to the enhancement of lactic acid production during the batch fermentation by indigenous microorganisms. Results revealed an optimum set of conditions for lactic acid production at a pH value of 6.5 and a fermentation period of 3.5 days at 37 °C. Under these conditions lactic acid production reached a value of 23.07 g/L, which was very similar to the mathematically predicted ones, thus verifying the accuracy of the experimental design. This optimum set of conditions was further employed to examine the production of lactic acid under continuous fermentation operation. Furthermore, concentrations of volatile fatty acids and ethanol were monitored and found to be relatively low, with ethanol being the dominant by-product of fermentation, indicating the presence of heterofermentative bacteria in the food wastes. A final step of downstream process was performed resulting in the successful recovery of lactic acid with purity over 90%.
... Therefore, HLa production has been reported through dark fermentation from OSW and FW [9,10]. This process consists of two steps, hydrolysis and acidogenesis, in which bioenergy and value-added compounds (e.g., butanol, succinic acid, and HLa) are obtained, allowing for the proper disposal and valorization of the organic waste [11][12][13][14]. ...
... However, most of these contributions must be confirmed or clarified [22]. In this sense, LAB such as Lactobacillus casei, L. plantarum, L. delbrueckii, and Pediococcus acidilactici have been evaluated as inoculum for HLa production from FW [12,23]. The advantages reported when pure cultures are employed include high yields, optical purity, and the ability to use a wide range of substrates [24]. ...
... It is important to note that HLa production may vary based on the initial pH, as well as the type and concentration of the substrate [26,28,30]. For restaurant and kitchen waste, studies have reported an HLa production range of 14.0 to 40.0 g/L during fermentation at an initial pH of 6.0-6.5 and a substrate concentration of more than 100.0 gVS/L [12,31]. ...
This work aimed to evaluate the effect of the sources of organic solid waste on lactic acid (HLa) production. Organic fractions from cafeteria (CW), market (MW), and recycling plant (RW) wastes were used as substrates. HLa production during the self-fermentation of CW, MW, and RW, as well as during the fermentation of each substrate with anaerobic sludge (CW + sludge, MW + sludge, and RW + sludge), was evaluated in batch tests at 37 °C, initial pH of 6.5, and 150 rpm. Subsequently, the initial pH and substrate concentration of self-fermentation of CW were optimized using a central composite design. The highest HLa production was observed in the self-fermentation of CW, where several Lactobacillus species predominated in the microbial community. The higher value of HLa production using CW (20.7 g/L) was obtained at a pH of 7.29 and 115.5 gVS/L. In the optimization tests, Lactobacillus and Weissella spp. were identified as the dominant lactic acid bacteria; however, only Lactobacillus species were associated with the highest HLa production.
... Due to their high sugar content and relatively long shelf life, dates offer many technological possibilities; depending on the processing they undergo (Rambabu et al., 2020). Indeed, dates can be used as raw material for the production of various metabolites [7][8][9]). This richness of dates is a renewable resource that should be used efficiently in biotechnology. ...
... Indeed, the use of microorganisms is essential to achieve these specific objectives. Among these, we can mention the possibilities of bioconversions and transformations of this source into lactic acid, which seem to be a promising and beneficial alternative, given the growing interest that this metabolite has shown in recent years [9]. ...
... Unfortunately, this kind of process requires high cost substrates (glucose, lactose,...), which make its use impractical. However, starchy materials, such as whey, starch hydrolysates and wheat can serve as a carbon source and are potential raw materials for lactic acid production [9,12,13]. In this kind of process, the culture medium is a crucial element for the growth of these bacteria and consequently the production of biomass and/or metabolites of interest, which absolutely requires the grouping of optimal conditions of nutritional qualities and technological parameters of the raw materials committed at low cost and market availability [14]. ...
We have successfully applied in this work the response surface methodology (RSM) involving central
composite planes (CCD) in order to study the effect of the temperature of incubation (x1
), pH (x2
) and
Inoculum size (x3
) on lactic acid production by the Lactococcus lactis DBH10 strain. After statistical
analysis, the quadratic terms of the variable (x1
2
, x2
2
, x3
2
) as well as those of the variables (x2
, x3
) in
linear terms and their interactions (x1
x2
; x1
x3
) were found to have significant effects on the response of
interest. The analysis of the second order polynomial regression model obtained by multiple regression
analysis, allowed us to reach a maximum lactic acid concentration of 486 ± 2.4 °D. The mathematical
relationship of lactic acid production by Lactococcus lactis DBH10 strain related to the three significant
independent variables was performed by a satisfactory fitting model. The predicted values were found
to be in good agreement with the experimental values, displaying a coefficient of determination of R2 =
0.989, demonstrating good significance of the proposed model. The adjustment of the levels of the factors
predicted by the model resulted in a maximum lactic acid concentration, when the optimal combination
of inculum size, temperature, and pH, are respectively at 2.8% (v/v), 21.5 °C and 4.8. The Validation of
the predicted model was carried out by performing three more experiments at the optimal levels of these
variables, thus confirming its robustness
... In the study, it was observed that the large inoculum size and substrate concentration resulted in a high concentration of lactic acid (26.8 g/L on average), but not a high yield of its production (0.20 g/g) [128]. A different approach to the exploitation of FW for lactic acid production was developed by Anagnostopoulou et al. [129], who performed fermentation using native microflora with the addition of two lactic acid bacteria (L. plantarum BS17 and L. casei BP2). ...
... plantarum BS17 and L. casei BP2). The study showed the best lactic acid production (23.07 g/L) at pH 6.5, at 37 • C and a fermentation period of 3.5 days [129]. The literature also reports a study of lactic acid production from food waste under industrial conditions. ...
The main tenets of the sustainable food production model are to reduce the adverse environmental impacts of production and to use available resources more efficiently. The sustainable food production model allows companies to adapt their strategies to current challenges and requirements while maintaining long-term production stability and competitiveness. To ensure that sustainable food chain participants implement appropriate practices, research is being conducted to develop new solutions. Among the important issues that are of great interest to researchers is the use of lactic acid bacteria (LAB). These bacteria play a pivotal role in sustainable food production, encompassing environmental, economic, and social aspects. The following article highlights recent innovations and advancements in LAB applications, contributing to enhanced efficiency and sustainable development of food products. By fermenting food, LAB effectively enhances food safety, prolong shelf life, and augment nutritional values, while simultaneously eliminating or outcompeting foodborne pathogens, thus preventing food poisoning. This article underscores these often-overlooked aspects of LAB, such as the critical role of fermented food in sustaining humanity during challenging times, by providing essential nutrients, and supporting health through its unique preservative and probiotic properties. It also points out the lesser-known applications of these microorganisms, including the degradation of organic waste or biogas and bioplastics production.
... For instance, a downstream purification system may include a combination of different membrane separation processes (such as UF and NF), ion exchange, and vacuum-assisted evaporation [10] to reach a purity level of > 99.5%. Another, hybrid-membrane purification process that led to high-quality LA (> 90.0% purity) combined concentration, ultrasonic liquid-liquid extraction, phase separation, and distillation to recover and purify LA from the fermentation broth [11]. Although, high LA purity was achieved, the process was proven quite complex with low recovery rate, mainly due to the liquid-liquid extraction process. ...
Background
A potential alternative to lactic acid production through sugar fermentation is its recovery from grass silage leachate. The separation and purification of lactic acid from fermentation broths remain a key issue, as it amounts to up to 80% of its industrial production cost. In this study, a genetically engineered E. coli strain (A1:ldhA), that cannot catabolize lactic acid, has been used to selectively remove impurities from a synthetic medium comprising typical components (i.e., glucose and acetic acid) of green grass silage leachate. A systematic approach has been followed to provide a proof-of-concept for a bio-purification process of lactic acid solutions in a membrane bioreactor operating in semi-continuous mode.
Results
The synthetic medium composition was initially optimized in shake-flasks experiments, followed by scale-up in bench-scale bioreactor. Complete (i.e., 100%) and 60.4% removal for glucose and acetic acid, respectively, has been achieved in batch bioreactor experiments with a synthetic medium comprising 0.5 g/L glucose and 0.5 g/L acetic acid as carbon sources, and 10 g/L lactic acid; no lactic acid catabolism was observed in all batch fermentation tests. Afterwards, a hybrid biotechnological process combining semi-continuous bioreactor fermentation and ultrafiltration membrane separation (membrane bioreactor) was applied to in-situ separate purified medium from the active cells. The process was assessed under different semi-continuous operating conditions, resulting in a bacteria-free effluent and 100% glucose and acetic acid depletion, with no lactic acid catabolism, thus increasing the purity of the synthetic lactic acid solution.
Conclusions
The study clearly demonstrated that a bio-purification process for lactic acid employing the engineered E. coli strain cultivated in a membrane bioreactor is a technically feasible concept, paving the way for further technological advancement.
... For instance, a downstream puri cation system may include a combination of different membrane separation processes (such as UF and NF), ion exchange, and vacuum-assisted evaporation [10] to reach a purity level of > 99.5%. Another, hybrid-membrane puri cation process that led to high-quality LA (> 90.0% purity) combined concentration, ultrasonic liquid-liquid extraction, phase separation, and distillation to recover and purify LA from the fermentation broth [11]. Although, high LA purity was achieved, the process was proven quite complex with low recovery rate, mainly due to the liquid-liquid extraction process. ...
Background: A potential alternative to lactic acid production through sugar fermentation is its recovery from grass silage leachate. The separation and purification of lactic acid from fermentation broths remains a key issue, as it amounts to up to 80% of its industrial production cost. In this study, a genetically engineered E. coli strain (A1:ldhA), that cannot catabolize lactic acid, has been used to selectively remove impurities from a synthetic medium comprising typical components (i.e. glucose and acetic acid) of green grass silage leachate. A systematic approach has been followed to provide a proof-of-concept for a bio-purification process of lactic acid solutions in a membrane bioreactor operating in semi-continuous mode.
Results: The synthetic medium composition was initially optimized in shake-flasks experiments, followed by scale-up in bench-scale bioreactor. Complete (i.e. 100%) and 60.4% removal for glucose and acetic acid, respectively, has been achieved in batch bioreactor experiments with a synthetic medium comprising 0.5 g/L glucose and 0.5 g/L acetic acid as carbon sources, and 10 g/L lactic acid; no lactic acid catabolism was observed in all batch fermentation tests. Afterwards, a hybrid biotechnological process combining semi-continuous bioreactor fermentation and ultrafiltration membrane separation (membrane bioreactor) was applied to in-situ separate purified medium from the active cells. The process was assessed under different semi-continuous operating conditions, resulting in a bacteria-free effluent and 100% glucose and acetic acid depletion, with no lactic acid catabolism, thus increasing the purity of the synthetic lactic acid solution.
Conclusion: The study clearly demonstrated that a bio-purification process for lactic acid employing the engineered E. coli strain cultivated in a membrane bioreactor is a technically feasible concept, paving the way for further technological advancement.
... The sugar metabolism and LA production of E. faecalis was studied in batch modes using sucrose and mixed sugars [55]. Batch fermentation could also be used to evaluate the efficacy of producing LA from renewable substrates and develop the process [56]. Mathematical LA batch fermentation models were analyzed to estimate the process indicators [57]. ...
Lactic acid plays an important role in industrial applications ranging from the food industry to life sciences. The growing demand for lactic acid creates an urgent need to find economical and sustainable substrates for lactic acid production. Agricultural waste is rich in nutrients needed for microbial growth. Fermentative production of lactic acid from non-food-competing agricultural waste could reduce the cost of lactic acid production while addressing environmental concerns. This work provided an overview of lactic acid fermentation from different agricultural wastes. Although conventional fermentation approaches have been widely applied for decades, there are ongoing efforts toward enhanced lactic acid fermentation to meet the requirements of industrial productions and applications. In addition, agricultural waste contains a large proportion of pentose sugars. Most lactic-acid-producing microorganisms cannot utilize such reducing sugars. Therefore, advanced fermentation techniques are also discussed specifically for using agricultural waste feedstocks. This review provides valuable references and technical supports for the industrialization of lactic acid production from renewable materials.
... Food ingredient (preservative flavouring) and bioplastic (poly-lactic acid) production [121] Mussel meat waste Enzymatic hydrolysis Extract rich in proteins and bioactive peptides Functional food ingredients with antioxidant and anti-hypertensive properties [122] Sustainability 2023, 15, 10571 11 of 21 ...
Hunger (811 million people, 2020) and food waste (931 million tonnes annually, 2020) are long-standing interconnected challenges that have plagued humankind for centuries. Food waste originates from various sources, including consumption habits and failures within the food supply chain. Given the growing concerns regarding food insecurity, malnutrition, and hunger, there is a pressing need to recover and repurpose as much food waste as possible. A growing body of knowledge identifies the valorisation (including upcycling) of food waste as one of the strategies to fight hunger by positively impacting food availability and food security. This paper evaluates the potential role of food waste valorisation, including upcycling, in reducing global hunger. A literature search was conducted to examine how converting food waste into value-added products, such as food formulations and farming inputs, can contribute to increasing food availability. The benefits of waste-to-food operations in improving food availability through producing food ingredients and products from materials that would have been wasted or discarded otherwise were discussed.
... The concentration of VFAs was quantified once per week by using gas chromatography (GC-2010 Pro, Shimadzu, Japan), equipped with flame ionization detector (FID) and the Agilent J & W Capillary Column (30 m length, 0.5 mm inner diameter, film thickness 1.0 µm) with helium as the carrier gas, according to the protocol of Anagnostopoulou et al. (2022). The quantification of VFAs assessed by using the respective calibration curves, and the data analyzed with the use of LabSolutions Software v5.106. ...
Packing materials improve biological methanation efficiency in Trickle Bed Reactors. The present study, which lies in the field of energy production and biotechnology, entailed the evaluation of commercial pelletized activated carbon and Raschig rings as packing materials. The evaluation focused on monitoring process indicators and examining the composition of the microbial community. Activated carbon resulted in enhanced methane purity, achieving a two-fold higher methane percentage than Raschig rings, maintaining a stable pH level within a range of 7-8 and reducing gas retention time from 6 h to 90 min. Additionally, the digestate derived from biogas plant was found to be a sufficient nutrient source for the process. Fermentative species with genes for β-oxidation, such as Amaricoccus sp. and Caloramator australicus could explain the production of hexanoic and valerate acids during reactor operation. Based on the physical properties of packing materials, the efficiency of biological methanation could be maximized.
... From this perspective, the lower biogas production of the LufTiO2P25 and Control batches may be associated with the accumulation of organic acids since the beginning of the experiments, which are responsible for the reduction of the operational pH (Arun et al., 2022). As was observed by Anagnostopoulou et al. (2022) e Wainaina et al. (2020), which highlighted that better yields of volatile fatty acids corresponded to lower yields of hydrogen, which is attributed to the potential acid inhibition caused by hydrogen-producing microorganisms. ...
... Utilizing Household food waste (HFW) as a primary resource is a significant problem because it is challenging to recover produced HFW from various locations and to manage it after recovery. Microbes may find HFW to be an obvious target due to humidity and total carbohydrate, which could cause significant deterioration [93]. The variability of HFW, which is significantly impacted by the location from which the wastes are obtained, presents additional difficulty. ...
There is worldwide generation of food waste daily in significant amounts, leading to depletion of natural resources and deteriorating air quality. One-third of global food produced is wasted laterally with the food value chain. Carbon footprint is an efficient way of communicating the issues related to climate change and the necessity of changing behavior. Valorization or utilization of food wastes helps in resolving issues related to environment pollution. Reduction in the carbon footprint throughout the chain of food supply makes the whole process eco-friendly. Prevailing food waste disposal systems focus on their economic and environmental viability and are putting efforts into using food waste as a resource input to agriculture. Effective and advanced waste management systems are adopted to deal with massive waste production so as to fill the gap between the production and management of waste disposal. Food waste biorefineries are a sustainable , eco-friendly, and cost-effective approach for the production of platform chemicals, biofuels, and other bio-based materials. These materials not only provide sustainable resources for producing various chemicals and materials but have the potential to reduce this huge environmental burden significantly. In this regard, technological advancement has occurred in past few years that has proven suitable for tackling this problem.
... In order to improve the conversion efficiency of wastewater, we investigated the effects of fermentation conditions on the total acid content of vinegar through the single-factor experiments and the response surface methodology analysis. The results showed that the influence order was inoculation amount > fermentation time > initial alcohol content, and the interaction between fermentation temperature and initial alcohol content had a significant influence on the conversion rate of acetic acid, and the interaction between inoculation amount and the initial alcohol had a significant influence on the yield of acetic acid [24]. Under the optimal fermentation conditions, an inoculation amount of 10.61%, initial alcohol content of 4.90%, fermentation temperature of 29.62 °C, fermentation time of 75.21 h, the predicted total acid content was 3.85 g 100 mL −1 , which is consistent with the experimental results of 3.80 ± 0.02 g 100 mL −1 . ...
The utilization of wastewater in food processing factory has become one of the foremost essential and challengeable problems. In this study, cabbage wastewater was used for a mixed fermentation to obtain a high ester vinegar. The effect of fermentation conditions on the total acid content and total ester content of vinegar was investigated through single-factor experiments and response surface methodology analysis. Under the optimal fermentation conditions of 10.61% inoculation amount, 4.9% initial alcohol content, 29.62 °C fermentation temperature, 75.21 h fermentation time, and the exogenous esterification addition amount of 0.6%. The blending vinegar has a total acid content of 3.80 g 100 mL−1 and a total ester content of 30.52 mg mL−1. The significant flavor components in the blending vinegar of the ethyl lactate with a pleasant aroma accounted for 22.15% and the ethyl acetate with a strong fruit aroma accounted for 11.37%.
... Volatile fatty acids (VFAs) are organic acids with a low molecular weight and hydrophilic characteristics. They are widely used in the chemical, leather, food, pharmaceutical and cosmetic industries (Anagnostopoulou et al., 2022). The production from fossil fuels (mostly petroleum) is unsustainable and it pollutes the environment, contributing to the generation of greenhouse gases. ...
Due to its high amount of organic and biodegradable components that can be recycled, biowaste is not only a major cause of environmental contamination, but also a vast store of useful materials. The transformation of biowaste into energy and resources via biorefinery is an unavoidable trend, which could aid in reducing carbon emissions and alleviating the energy crisis in light of dwindling energy supplies and mounting environmental difficulties related with solid waste. In addition, the current pandemic and the difficult worldwide situation, with their effects on the economic, social, and environmental aspects of human life, have offered an opportunity to promote the transition to greener energy and sources. In this context, the current advancements and possible trends of utilizing widely available biowaste to produce key biofuels (such as biogas and biodiesel) and resources (such as organic acid, biodegradable plastic, protein product, biopesticide, bioflocculant, and compost) are studied in this review. To achieve the goal of circular bioeconomy, it is necessary to turn biowaste into high-value energy and resources utilizing biological processes. In addition, the usage of recycling technologies and the incorporation of bioconversion to enhance process performance are analyzed critically. Lastly, this work seeks to reduce a number of enduring obstacles to the recycling of biowaste for future use in the circular economy. Although it could alleviate the global energy issue, additional study, market analysis, and finance are necessary to commercialize alternative products and promote their future use. Utilization of biowaste should incorporate a comprehensive approach and a methodical style of thinking, which can facilitate product enhancement and decision optimization through multidisciplinary integration and data-driven techniques.
... For instance, FW under a two-step pilot-scale AD could produce a maximum of H 2 (170 L (kg TVS), 40%), methane (750 L, 67%), and volatile fatty acids (14 g COD L -1 ), respectively, at varying pH of 5.0-8.0 (Gottardo et al., 2017). More recently, Anagnostopoulou et al. (2022) alternatively showed that household FW could be valorized for lactic acid fermentation under indigenous microbiota, resulting in 23.07 g L -1 of lactic acid at pH 6.5, and a temperature of 37 • C within 3.5 days, respectively. ...
Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.
This study aims to integrate a novel bio-purification process employing an engineered E. coli strain in the downstream processing of lactic acid (LA) fermentation broths from low-cost renewable biological feedstocks. Fermentation broth of candy waste and digestate mixture was used as a real biological feedstock. An engineered E. coli strain that selectively catabolize impurities without catabolizing LA was initially adapted on the biological feedstock, followed by shake flask experiments to prove the bio-purification concept. Scale-up and validation in a bench-scale bioreactor followed, before developing a semi-continuous membrane bioreactor (MBR) bio-purification process. The MBR bio-purification was assessed with biological feedstocks which simulated ultrafiltration or nanofiltration permeates. Incomplete removal of impurities and increased fouling was observed in the case of the ultrafiltration permeate. Contrarily, the nanofiltration permeate was successfully treated with MBR bio-purification, since low membrane fouling, 100% maltose and acetic acid removal, and no LA catabolism was achieved. MBR bio-purification as a post-treatment step in the downstream processing of LA was demonstrated as a promising technology for increasing the purity of LA solutions.
A large amount of household food waste (HFW) is generated yearly and may negatively impact the environment and human health. The recovery of value‐added chemicals lactic acid (LA) from HFW through anaerobic treatment is a promising approach. However, it remains a challenge to increase the LA yield. In this paper, the LA production from HFW was enhanced by Lactobacillus rhamnosus ATCC 7469 through simultaneous saccharification and fermentation (SSF). The results showed that the mixed commercial enzymes of plant enzymes (E1), animal proteases (E2), and glucoamylase (E3) were more conducive to LA production than those used separately. Compared to the separate hydrolysis and fermentation (SHF), the LA production increased by 14% in the SSF, and the glucose concentration showed different change rules. Additionally, an average LA concentration of 47.7 g L –1 was obtained by repeated batch fermentation through SSF. However, the maximum LA concentration decreased with the fermentation ongoing. The trend of decreasing LA production could be improved by repeated batch fermentation with supplementary inoculation.
Traditional plastics represent a tremendous threat to the environment because of increases in polluting manufacturing as well as their very extended degradation time. Polyhydroxyalkanoates (PHAs) are polymers with similar performance to plastic but are compostable and synthesizable from renewable sources and therefore could be a replacement for fossil-based plastics. However, their production costs are still too high, thus demanding the investigation of new and cheap substrates. In this sense, agricultural wastes are attractive because they are inexpensive and largely available. Specifically, fruit and vegetables are rich in sugars that could be fermented into PHAs. In this work two strains, Cupriavidus necator DSM 545 and Hydrogenophaga pseudoflava DSM 1034, well-known PHA-producing microbes, were screened for their ability to grow and accumulate PHAs. Ten different fruit and vegetable processing waste streams, never before reported in combination with these strains, were tested. Residues from red apple and melon were found to be the most suitable feedstocks for PHA production. Under specific selected conditions, C. necator DSM 545 accumulated up to 7.4 and 4.3 g/L of 3-hydroxybutyrate (3HB) from red apple and melon, respectively. Copolymer production was also obtained from melon. These results confirm the attractiveness of food processing waste as a promising candidate for PHA production. Ultimately, these novel substrates draw attention for future studies on process optimization and upscaling with C. necator.
Bioconversion is an important method for transforming food waste (FW) into high value-added products, rendering it harmless, and recycling resources. An artificial microbial consortium (AMC) was constructed to produce FW-based lipopeptides in order to investigate the strategy of FW bioconversion into value-added products. Exogenous fatty acids as a precursor significantly improved the lipopeptide production of Bacillus amyloliquefaciens HM618. To enhance fatty acid synthesis and efflux in AMC, the recombinant Yarrowia lipolytica YL21 (strain YL21) was constructed by screening 12 target genes related to fatty acids to replace exogenous fatty acids in order to improve lipopeptide production. The levels of fengycin, surfactin, and iturin A in the AMC of strains HM618 and YL21 reached 76.19, 192.80, and 31.32 mg L-1, increasing 7.24-, 12.13-, and 3.23-fold compared to the results from the pure culture of strain HM618 in flask with Landy medium, respectively. Furthermore, free fatty acids were almost undetectable in the co-culture of strains HM618 and YL21, although its level was around 1.25 g L-1 in the pure culture of strain YL21 with Landy medium. Interestingly, 470.24 mg L-1 of lipopeptides and 18.11 g L-1 of fatty acids were co-produced in this AMC in a bioreactor with FW medium. To our knowledge, it is the first report of FW biotransformation into co-produce of lipopeptides and fatty acids in the AMC of B. amyloliquefaciens and Y. lipolytica. These results provide new insights into the biotransformation potential of FW for value-added co-products by AMC.
Lactic acid is an essential platform chemical with various applications in the chemicals, food, pharmaceutical, and cosmetic industries. Currently, the demand for lactic acid is driven by the role of lactic acid as the starting material for the production of bioplastic polylactide. Microbial fermentation for lactic acid production is favored due to the production of enantiomerically pure lactic acid required for polylactide synthesis, as opposed to the racemic mixture obtained via chemical synthesis. The utilization of first-generation feedstock for commercial lactic acid production is challenged by feedstock costs and sustainability issues. Macroalgae are photosynthetic benthic aquatic plants that contribute tremendously towards carbon capture with subsequent carbon-rich biomass production. Macroalgae are commercially cultivated to extract hydrocolloids, and recent studies have focused on applying biomass as a fermentation feedstock. This review provides comprehensive information on the design and development of sustainable and cost-effective, algae-based lactic acid production. The central carbon regulation in lactic acid bacteria and the metabolism of seaweed-derived sugars are described. An exhaustive compilation of lactic acid fermentation of macroalgae hydrolysates revealed that lactic acid bacteria can effectively ferment the mixture of sugars present in the hydrolysate with comparable yields. The environmental impacts and economic prospects of macroalgal lactic acid are analyzed. Valorization of the vast amounts of spent macroalgal biomass residue post hydrocolloid extraction in a biorefinery is a viable strategy for cost-effective lactic acid production.
China is vigorously promoting garbage classification, but the treatment of classified waste, especially household food waste (HFW) has yet to be studied. Lactic acid (LA), a high value-added platform molecule has broad market prospects. Although there have been many studies on the production of LA from food waste, open fermentation often produces lots of by-products, while the traditional fermentation under a pure bacteria system often requires the saccharification process, which increases the production cost. We sought to analyze the comprehensive properties of classified HFW in Shanghai, then to produce LA by inoculating lactic acid bacteria (LAB) directly. The effects of strains, temperature, sterilized or not, initial pH, inoculum size, and substrate concentration on LA production were investigated. HFW was rich in nutrients and growth factors which provided the possibility for direct LA production from HFW by inoculating LAB. The results showed that Lactobacillus rhamnosus ATCC 7469, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus all could be used as the inoculum, however, no significant synergistic effect of the three strains on LA production was found. LA concentration of 30.25 g/L at 37 °C, pH 6.8 could be obtained by inoculating Lactobacillus rhamnosus ATCC 7469 from sterilized HFW. High inoculum size and substrate concentration resulted in high LA concentration, but not high LA yield. The result of ANOVA indicated that there was a significantly positive relationship between substrate concentration and LA concentration (r = 0.942, p < 0.01), while no statistically significant difference between these groups at different inoculum size was evident (p = 0.318). In addition, an average LA concentration of 26.8 g/L, LA yield of 0.20 g/g TCOD was obtained by repeated batch fermentation for 32 d.
Lactic acid is a naturally existing organic acid, which may be applied in many different branches of industrial application, for example cosmetics, pharmaceutics, chemicals, food, and nowadays also in medicine. It can be made in sugar fermentation process from renewable raw materials, which means, that is the ecological product that has enjoyed great popularity in recent years. In 2010, the US Department of Energy published a report, which means about lactic acid as a potential building element for the future technology, and demand on that product is still growing year by year [1, 2].
The lactic acid molecule naturally exist in plants, microorganisms and animals and can also be produced by carbohydrate fermentation or chemical synthesis from coal, petroleum products or natural gas. In industry, lactic acid can be produced by chemical synthesis or fermentation.
Although racemic lactic acid is always produced chemically from petrochemical sources, optically pure L(+) – or D(-) – lactic acid form can be obtained by microbial fermentation of renewable resources when the appropriate microorganism is selected. Depending on the application, one form of optically pure LA is preferred over the other. Additionally, microbial fermentation offers benefits including cheap renewable substrates, low production temperatures and low energy consumption. Due to these advantages, the most commonly used biotechnological production process with the use kind of biocatalysts – that is lactic acid bacteria [3, 4].
The cost of raw materials is one of the major factors in the economic production of lactic acid. As substrate costs cannot be reduced by scaling up the process extensive research is currently underway to find new substrates for the production of LA [5].
These searches include starch raw materials, lignocellulosic biomass, as well as waste from the food and refining industries. Here, the greatest attention is still drawn to molasses and whey as the largest sources of lactose, vitamins and carbohydrates, as well as glycerin – a by-product of biodiesel component production process [6.
Focusing on the importance of lactic acid and its subsequent use as a product, but also a valuable raw material for polymerization (exactly to PLA), this review summarizes information about the properties and applications of lactic acid, as well as about its production and purification processes.
Environmental problems, such as global warming and plastic pollution have forced researchers to investigate alternatives for conventional plastics. Poly(lactic acid) (PLA), one of the well-known eco-friendly biodegradables and biobased polyesters, has been studied extensively and is considered to be a promising substitute to petroleum-based polymers. This review gives an inclusive overview of the current research of lactic acid and lactide dimer techniques along with the production of PLA from its monomers. Melt polycondensation as well as ring opening polymerization techniques are discussed, and the effect of various catalysts and polymerization conditions is thoroughly presented. Reaction mechanisms are also reviewed. However, due to the competitive decomposition reactions, in the most cases low or medium molecular weight (MW) of PLA, not exceeding 20,000–50,000 g/mol, are prepared. For this reason, additional procedures such as solid state polycondensation (SSP) and chain extension (CE) reaching MW ranging from 80,000 up to 250,000 g/mol are extensively investigated here. Lastly, numerous practical applications of PLA in various fields of industry, technical challenges and limitations of PLA use as well as its future perspectives are also reported in this review.
Lactic acid is an organic compound produced via fermentation by different microorganisms that are able to use different carbohydrate sources. Lactic acid bacteria are the main bacteria used to produce lactic acid and among these, Lactobacillus spp. have been showing interesting fermentation capacities. The use of Bacillus spp. revealed good possibilities to reduce the fermentative costs. Interestingly, lactic acid high productivity was achieved by Corynebacterium glutamicum and E. coli, mainly after engineering genetic modification. Fungi, like Rhizopus spp. can metabolize different renewable carbon resources, with advantageously amylolytic properties to produce lactic acid. Additionally, yeasts can tolerate environmental restrictions (for example acidic conditions), being the wild-type low lactic acid producers that have been improved by genetic manipulation. Microalgae and cyanobacteria, as photosynthetic microorganisms can be an alternative lactic acid producer without carbohydrate feed costs. For lactic acid production, it is necessary to have substrates in the fermentation medium. Different carbohydrate sources can be used, from plant waste as molasses, starchy, lignocellulosic materials as agricultural and forestry residues. Dairy waste also can be used by the addition of supplementary components with a nitrogen source.
The growing need for Lactobacillus bacteria usage in industry and the expending probiotic market led to a search for new cost-e�cient fermentation media from which a high yield of these bacteria could be obtained. The following study aimed to elaborate cultivation medium, for Lactobacillus spp. growth, which main components would be wheat, maize, barley, and rye flours. The optimal temperature for Lactobacillus growth in new semi-solid fermentation (SSF) medium, water content, and pH of the medium were analyzed by the plate count method. It was established, that the highest bacteria counts were obtained from cultures conducted in the SSF medium with flours to water ratio of 1:1.5 with a natural pH of 6.0 at 37 �C. Subsequently, the growth kinetics of analyzed strains, in both MRS and the SSF media, were studied. The newly designed media contributed to the increased duration of selected Lactobacillus strains lag phase, which varied from 1.98 to 5.64; nevertheless, the maximum growth rate of the strains was two times higher in the SSF medium rather than in MRS, which also resulted in shorter generation time. The developed medium has the potential to become a new cost-e�cient fermentation medium for Lactobacillus spp.
Source-sorted organic portion of municipal solid waste (bio-waste) can be fermented to lactic acid, a platform chemical widely used in the production of biodegradable polymers, green solvents, and chemicals. In the present study, fermentation of bio-waste using lactic acid producing bacterium (LAB) Lactobacillus delbrueckii was investigated. Results showed that adding 10% (v/v) of L. delbrueckii as LAB inoculum along with pH adjustment to 6.2 had the highest lactic acid yield (0.65 g/gtotal sugars). Nevertheless, pH adjustment without bio-augmentation could also result in relatively high yield of lactic acid (0.57 g/gtotal sugars). Furthermore, enzymatic hydrolysis was applied to boost the lactic acid production slightly increasing the yield to 0.72 g/gtotal sugars. Thus, fermentative production of lactic acid can be achieved without the addition of enzymes to reduce production costs. Overall, the results indicate that bio-waste could be a suitable substrate for the production of lactic acid.
The development of sustainable methods with robust strains and renewable substrates for the production of high-value chemicals has gained much attention recently. This study investigates the effect of ten different microbial strains for lactic acid production from food waste through simultaneous saccharification and fermentation process at optimal conditions of pH 5.5–6.5 at 30 °C. The highest lactic acid concentration of 18.69 g L-1 was obtained from Lacobacillus manihotivorans DSM 13343, followed by 17.03 g L-1 from Lactobacillus plantarum DSM 20174 and 15.88 g L-1 from mixed culture during fermentation of food waste, whereas the strains produced only 12.72 g L-1, 17.75 g L-1, and 9.38 g L-1 respectively from MRS broth, therefore showing that the food waste was a superior substrate compared to the MRS broth for lactic acid fermentation. The maximum lactic acid yield was 0.73 g g-1, 0.71 g g-1, and 0.69 g g-1 with Lacobacillus manihotivorans DSM 13343, Lactococcus lactis subsp. lactis DSM 20481, and Lactobacillus plantarum DSM 20174 respectively with high selectivity for lactic acid up to 84%. Furthermore, this study has achieved significant lactic acid production with increased substrate utilization in lower processing time and reactor volume.
This study investigated the effects of pH, total solids (TS) content, and enzymatic pretreatment on lactic acid (LA) production from food waste with indigenous microbiota. A multilevel factorial design was applied to all the essential factors for making LA production the most efficient and productive. The experimental data revealed that all the tested factors had a significant effect on the LA produced. The production of LA was progressively increased with the increase of TS content from 50 to 150 g-TS/L. With enzymatic pretreatment, the maximum production of volatile fatty acids (VFAs) and LA was, respectively, 26.17 g/L and 12.87 g/L at a pH of 6 and 150 g-TS/L. A LA yield of 0.09 g/g-TS with a productivity of 1.29 g/L day was achieved at mesophilic temperature of 37 °C and optimal operating conditions. Interestingly, the production of VFAs was 2.6-fold, and LA was 3-fold higher compared to those obtained with untreated food waste under same conditions. These results showed that enzymatically pretreated food waste at TS 15% can provide high production of VFAs and LA. The high selectivity of LA in the fermentative product, along with others, could make downstream processing economical. The multilevel factorial design predicted optimum conditions and presented a good agreement with a mean error of less than 5%.
Lactic acid (LA) is an organic compound used in several industries, such as food, textile, chemical, and pharmaceutical. The global interest in this product is due to its use for the synthesis of numerous chemical compounds, including polylactic acid, a biode-gradable thermoplastic and substitute for petroleum-derived plastics. An in-depth overview of the use of industrial and household wastes as inexpensive substrates in order to reduce the cost of LA production is presented. A review is carried out of the biotech-nological aspects that must be taken into account when using some wastes with high transformation potential to produce LA in a submerged culture, as well recommendations for their use. The advantages and disadvantages of different types of treatments used for the transformation of waste into suitable substrates are considered. Several methods of fermentation, as well as genetic strategies for increasing the production, are summarized and compared. It is expected that in a few years there will be many ad-vances in these areas that will allow greater large-scale production of LA using agroindustrial or household wastes, with potential positive economic and environmental impact in some regions of the planet.
Lactic acid bacteria (LAB) are members of an heterogenous group of bacteria which plays a significant role in a variety of fermentation processes. The general description of the bacteria included in the group is gram-positive, non-sporing, non-respiring cocci or rods. An overview of the genetics of lactococci, Streptococcus thermophilus, lactobacilli, pediococci, leuconostocs, enterococci and oenococciis presented with special reference to their metabolic traits. The three main pathways in which LAB are involved in the manufacture of fermented foods and the development of their flavour, are (a) glycolysis (fermentation of sugars), (b) lipolysis (degradation of fat) and (c) proteolysis (degradation of proteins). Although the major metabolic action is the production of lactic acid from the fermentation of carbohydrates, that is, the acidification of the food, LAB are involved in the production of many beneficial compounds such as organic acids, polyols, exopolysaccharides and antimicrobial compounds, and thus have a great number of applications in the food industry (i.e. starter cultures). With the advances in the genetics, molecular biology, physiology, and biochemistry and the reveal and publication of the complete genome sequence of a great number of LAB, new insights and applications for these bacteria have appeared and a variety of commercial starter, functional, bio-protective and probiotic cultures with desirable properties have marketed.
A batch study was done for exploring the performance of eggshell powder (EGP) for adsorptive removal of carbaryl from aqueous solution. In the experiment, the operating factors were initial carbaryl concentration (5–20 mg L⁻¹), solution pH (2–10), adsorbent dose (0.01–0.1 g/100 ml) and contact time (10–60 min). For optimization, evaluation of the effects and interactions of the operating factors response surface modeling was applied and the influence of the factors was checked through a two-level four factor Box–Behnken design (BBD) model. The predicted data had shown good agreement (R² = 0.9985) with experimental data. Furthermore, the adsorption data were best fitted with Freundlich isotherm and pseudo-second-order kinetics. Thermodynamic parameters revealed that the adsorption of process was spontaneous and endothermic. Finally it can be concluded that the EGP can be used as an alternative adsorbent for the removal of carbaryl from aqueous medium.
Lactic acid is a naturally occurring organic acid that can be used in a wide variety of industries, such as the cosmetic, pharmaceutical, chemical, food, and, most recently, the medical industries. It can be made by the fermentation of sugars obtained from renewable resources, which means that it is an eco-friendly product that has attracted a lot of attention in recent years. In 2010, the U.S. Department of Energy issued a report that listed lactic acid as a potential building block for the future. Bearing the importance of lactic acid in mind, this review summarizes information about lactic acid properties and applications, as well as its production and purification processes.
This Brief explores the importance of lactic acid and fermentation in the modern food industry. Although it is usually associated with milk and dairy products, lactic acid can also be found in many other fermented food products, including confectionery products, jams, frozen desserts, and pickled vegetables. In this work, the authors explain how lactic acid is produced from lactose by Lactobacillus and Streptococcus cultures, and they also emphasise its important role as pH regulator and preservative, helping to the inhibition of microbial growth in fermented foods. The Brief discusses a wide range of lactic acid’s applications as a natural additive, curing or gelling agent, flavour, food carrier, solvent, and discoloration inhibitor, among others. Readers will also find a brief overview of the current analytical methods for the quantitative and qualitative determination of lactic acid in foods.
Lactic acid is a naturally occurring organic acid that can be used in a wide variety of industries, such as the cosmetic, pharmaceutical, chemical, food, and, most recently, the medical industries. It can be made by the fermentation of sugars obtained from renewable resources, which means that it is an eco-friendly product that has attracted a lot of attention in recent years. In 2010, the U.S. Department of Energy issued a report that listed lactic acid as a potential building block for the future. Bearing the importance of lactic acid in mind, this review summarizes information about lactic acid properties and applications, as well as its production and purification processes.
Lactic acid (LA) is a necessary industrial feedstock for producing the bioplastic, polylactic acid (PLA), which is currently produced by pure culture fermentation of food carbohydrates. This work presents an alternative to produce LA from potato peel waste (PPW) by anaerobic fermentation in a sequencing batch reactor (SBR) inoculated with undefined mixed culture from a municipal wastewater treatment plant. A statistical design of experiments approach was employed using set of 0.8L SBRs using gelatinized PPW at a solids content range from 30 to 50gL(-1), solids retention time of 2-4days for yield and productivity optimization. The maximum LA production yield of 0.25gg(-1) PPW and highest productivity of 125mgg(-1)d(-1) were achieved. A scale-up SBR trial using neat gelatinized PPW (at 80gL(-1) solids content) at the 3L scale was employed and the highest LA yield of 0.14gg(-1) PPW and a productivity of 138mgg(-1)d(-1) were achieved with a 1d SRT.
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Lactobacillus acidophilus is a commercially significant bacterial probiotic, originally isolated from the human gastrointestinal tract and designated Bacillus acidophilus in 1900. Throughout the development of methods to identify and characterise bacteria, L. acidophilus has undergone multiple taxonomic revisions and is now the type species of a phylogenetic subgroup in the highly diverse and heterogeneous Lactobacillus genus. As a result of the limitations of differentiating phenotypically similar species by morphological and biochemical means and revisionary nature of Lactobacillus taxonomy, the characterisation of L. acidophilus has struggled with misidentification and misrepresentation. In contrast, due to its global use as a probiotic supplement in functional foods, L. acidophilus sensu stricto is now one of the most well-characterised Lactobacillus species. Here, we establish the provenance of L. acidophilus strains, unpicking historical and current misidentifications of L. acidophilus, and reviewing the probiotic, genomic and physiological characteristics of this important Lactobacillus species.
The aim of this work was to study the fermentation of whey for the production of L(+) lactic acid using Lactobacillus casei. The effect of different process parameters such as pH of the medium, temperature, inoculum size, age of inoculum, agitation and incubation time was monitored to enhance the lactose conversion in whey to L(+) lactic acid. Fermentations were performed without any pH control. The optimization of the fermentation conditions resulted in significant decrease in fermentation time, besides increase in lactose conversion to lactic acid. The optimized process conditions resulted in high lactose conversion (95.62%) to L(+) lactic acid production (33.73 g/L) after an incubation period of 36 h.
Lactic acid is widely used in the food, cosmetic, pharmaceutical, and chemical indus-tries and has received increased attention for use as a monomer for the production of bio-degradable poly(lactic acid). It can be produced by either biotechnological fermentation or chemical synthesis, but the former route has received considerable interest recently, due to environmental concerns and the limited nature of petrochemical feedstocks. There have been various attempts to produce lactic acid efficiently from inexpensive raw materials. We present a review of lactic acid-producing microorganisms, raw materials for lactic acid production, fermentation approaches for lactic acid production, and various applications of lactic acid, with a particular focus on recent investigations. In addition, the future po-tentials and economic impacts of lactic acid are discussed.
MultiExperiment Viewer (MeV) is a freely available software application that puts modern bioinformatics tools for integrative
data analysis in the hands of bench biologists. MeV is a versatile microarray data analysis tool, incorporating sophisticated
algorithms for clustering, visualization, classification, statistical analysis, and biological theme discovery from single
or multiple experiments. This chapter gives an overview of MeV technical details and its use in a real setting.
The present research aims to investigate the individual and interactive effects of chlorine dose/dissolved organic carbon ratio, pH, temperature, bromide concentration, and reaction time on trihalomethanes (THMs) formation in surface water (a drinking water source) during disinfection by chlorination in a prototype laboratory-scale simulation and to develop a model for the prediction and optimization of THMs levels in chlorinated water for their effective control.
A five-factor Box-Behnken experimental design combined with response surface and optimization modeling was used for predicting the THMs levels in chlorinated water. The adequacy of the selected model and statistical significance of the regression coefficients, independent variables, and their interactions were tested by the analysis of variance and t test statistics.
The THMs levels predicted by the model were very close to the experimental values (R(2) = 0.95). Optimization modeling predicted maximum (192 μg/l) TMHs formation (highest risk) level in water during chlorination was very close to the experimental value (186.8 ± 1.72 μg/l) determined in laboratory experiments. The pH of water followed by reaction time and temperature were the most significant factors that affect the THMs formation during chlorination.
The developed model can be used to determine the optimum characteristics of raw water and chlorination conditions for maintaining the THMs levels within the safe limit.
Recently, research on the production of ethanol from waste has been accelerating for both ecological and economical reasons, primarily for its use as an alternative to petroleum based fuels. In this study, response surface methodology based 23 -full factorial central composite design was employed to optimize the parameters of ethanol production from Korean food waste leachate. The reducing sugar concentration of the food waste leachate determined by the dinitrosalicylic acid method was 75 g/L. A second order polynomial model was developed to evaluate the quantitative effects of temperature, pH and reducing sugar concentration in order to find an optimum condition for the ethanol production from food waste leachate. From the experimental result, maximum ethanol concentration of 24.17 g/L was obtained at the optimum condition of temperature (38 ºC), pH (5.45) and reducing sugar concentration (75 g/L). The experimental value (24.17 g/L) agreed very well with the predicted one (23.66 g/L), indicating the suitability of the model employed and the success of response surface methodology in optimizing the conditions of ethanol production from food waste leachate. Canonical analysis indicated that the stationary point was a saddle point for the ethanol yield. Despite being a waste, an ethanol yield of 0.32 g ethanol/g reducing sugar demonstrated the potential of food waste leachate as a promising biomass resource for the production of ethanol.
Slaughterhouse residues are greatly available and can pose a threat to the environment if not disposed of correctly. Such by-products can be proficiently processed into polyhydroxyalkanoates by accurately selected and developed bacterial strains. Cupriavidus necator DSM 545, one of the most efficient polyhydroxyalkanoates-producing strain, cannot grow well on fatty substrates. In this work, a recombinant lipolytic C. necator microbe was developed for the efficient conversion of slaughtering by-products into polyhydroxyalkanoates. Two lipase sequences, lipC and lipH of Pseudomonas stutzeri BT3, were effectively expressed in C. necator DSM 545. The engineered strain C. necator DSM 545 JR11, selected for the outstanding extracellular lipolytic activity, produced high levels of polyhydroxyalkanoates (nearly 65% of cell dry mass) from udder, jowl and membrane caul fat. This research is crucial to the cost-effective one-step processing of slaughterhouse waste into polyhydroxyalkanoates with useful applications in several industrial and medical sectors.
Solid biowastes (SBW) are organic residues from gardens and parks, food wastes from kitchens, organic municipal solid wastes and comparable side streams from food processing plants. Without proper treatment, SBW represent an environmental hazard. Several initiatives around the world are dedicated to developing more effective systems for the treatment of this constantly growing ‘resource’. The chemical composition of SBW, rich in carbohydrates, proteins and lipids, makes it a good substrate to produce biobased materials through fermentation. Amongst them, lactic acid (LA), considered one of the top ten green molecules of the future, has attracted huge interest because of its many uses as an intermediate chemical. This review gathers the most important learnings from fermentation of SBW to LA, providing an overview of the process steps while highlighting some of the current limitations to overcome. Despite their complexity, results suggest that some of the SBW could be good substrates in LA fermentations and that biosynthesis of LA should be regarded as part of the whole waste management solution.
Biotransformation of organic wastes into value-added products is gaining interest owing to waste management issues, exhaustion of fossil fuels and the demand for biodegradable plastics. Lactic acid is widely used for polymers, foods, beverages, medicines, cosmetics and clothing. However, the major obstacle in large-scale fermentation of lactic acid is achieving enhanced yield, productivity and optical purity with cheap resources. Therefore, we review methods and recovery techniques for production of microbial lactic acid using cheap fermentative substrates. New strategies allow to alleviate limitations associated with substrate inhibition, product inhibition, undesirable by-products, sensitivity to toxic compounds, inefficient utilization of mixed sugars and overuse of neutralizing agents. Efficient utilization of mixed sugars can be achieved with simultaneous saccharification and fermentation using mixed cultures, isolating carbon catabolic repression-negative strains and altering the metabolic pathway. Lactic acid productivity can be improved by co-culture, maintaining high cell density and periodically removing end-products accumulated in the fermentation medium. Inhibition by toxic compounds can be eliminated by using engineered feedstock which releases less inhibitors, by using inhibitor-tolerant microbes and by development of genetically engineered strains. Fed-batch fermentation was found to be better than other operation modes due to less substrate inhibition.
The high and easy degradable sugar content of source-sorted organic household (SSOHW) suggests it as a promising candidate for fermentative lactic acid production. The present study aimed to applied bio-augmentation strategy with different lactic acid bacteria (Lactobacillus delbrueckii or Pediococcus acidilactici) to improve lactic acid production from non-sterile SSOHW. The optimum operational temperature, initial pH and total solid loading during fermentation were essential for lactic acid production. Lactic acid concentration of 20.7 ± 0.3 and 16.8 ± 0.4 g/L were obtained by bio-augmenting Pediococcus acidilactici and Lactobacillus delbrueckii, respectively, achieving an increment of 36.2% and 10.5% compared to abiotic augmentation. A lactic acid yield of 0.73 g/g-sugar was achieved with addition of Pediococcus acidilactici, while the optical purity of LA was also improved by the bio-augmentation. Furthermore, response surface methodology along with the Box-Behnken model was applied to determine the optimal operational conditions (i.e. temperature, initial pH and total solid loading). Based on the outcome, the highest concentration and yield were 31.2 g/L and 0.735 g/g-sugar at temperature of 32.4 ˚C, initial pH of 8.0 and total solid loading of 105.0 g/L. Finally, the predicted value was validated by scale-up experiment, and the LA titer and yield of scale-up fermenter was well corresponding to predicted value. The bio-augmentation strategy and process optimization provided a simple and energy saving method for industrial LA production from SSHOW. With respect to environmental sustainability and cleaner production, the conversion of bio-waste to lactic acid is an advantageous waste management approach that will contribute to the transition from a petro-based economy towards the production and use of bio-based derived products thereby creating innovative value chains with lower carbon footprint and social responsibility.
Recent advances in amylolytic strain engineering for starch-to-ethanol conversion have provided a platform for the development of raw starch consolidated bioprocessing (CBP) technologies. Several proof-of-concept studies identified improved enzyme combinations, alternative feedstocks and novel host strains for evaluation and application under fermentation conditions. However, further research efforts are required before this technology can be scaled up to an industrial level. In this review, different CBP approaches are defined and discussed, also highlighting the role of auxiliary enzymes for a supplemented CBP process. Various achievements in the development of amylolytic Saccharomyces cerevisiae strains for CBP of raw starch and the remaining challenges that need to be tackled/pursued to bring yeast raw starch CBP to industrial realization, are described. Looking towards the future, it provides potential solutions to develop more cost-effective processes that include cheaper substrates, integration of the 1G and 2G economies and implementing a biorefinery concept where high-value products are also derived from starchy substrates.
The anaerobic digestion (AD) of municipal biopulp with two macroalgal biomasses (i.e. Saccharina latissima and Fucus serratus) was investigated at batch and continuously fed digesters at thermophilic conditions (54 ± 1 °C). At batch mono-digestion tests, municipal biopulp was associated with significantly higher methane production (549 ± 9 mLCH 4 /gVS) compared to both S. latissima (210 ± 13 mLCH 4 /gVS) and F. serratus (206 ± 37 mLCH 4 /gVS). Regarding batch co-digestion tests, the highest methane yield was achieved when the feedstock consisted of 80% VS of biopulp and 20% VS of macroalgal biomass and it corresponded to the single methane contributions. The batch results were confirmed by continuous mode operation experiments, for the mono-digestion of biopulp and subsequently, the co-digestion with S. latissima. A specific challenge encountered with macroalgae biomethanation is the high sodium content. Therefore, mathematical modelling was followed to predict the performance of continuous mode experiments under increased salinity conditions by simulating the addition of more saline feedstock. The experimental results were used to calibrate and validate the model. Modelling simulations revealed that usage of saline feedstocks can drastically inhibit a well-performing AD reactor.
Microbial dynamics in an upgrading biogas reactor system undergoing a more than two years-period at stable operating conditions were explored. The carbon dioxide generated during biomass degradation in the first reactor of the system was converted to methane into the secondary reactor by addition of external hydrogen. Considering the overall efficiency, the long-term operation period resulted in an improved biogas upgrading performance (99% methane content). However, a remarkable accumulation of acetate was revealed, indicating the enhancement of homoacetogenic activity. For this reason, a shift in the anaerobic digestion microbiome was expected and evaluated by 16S rRNA amplicon analysis. Results demonstrated that the most abundant archaeal species identified in the first time point, Candidatus Methanoculleus thermohydrogenotrophicum, was replaced by Methanothermobacter thermautotrophicus, becoming dominant after the community adaptation. The most interesting taxonomic units were clustered by relative abundance and six main long-term adaptation trends were found, characterizing functionally related microbes (e.g. homoacetogens).
Lactic acid is an already consolidated bioproduct in the world market. It has many applications, such as: the production of biodegradable polymers, substitution of plastics from oil, and new uses in medicine. Besides this, new applications are being discovered every year, especially in chemical industries as a building-block molecule. The lactic acid market is in constant growth and the fact that the final products are able to comply with environmental laws as green, renewable and biodegradable products contributes to the tendency of continuous growth in the next few years. With all of this in mind, this paper will explore the main aspects of the sector, as well as market tendencies, production chain, and innovation.
Food waste (FW) management by biological process is more attractive and eco-friendly approach than thermo-chemical conversion or landfilling. However, FW composition and physico-chemical and biological characteristics affect the overall biological process in terms of product yield and degradation rate. To overcome this major bottle neck, the pretreatment of FW is proposed. Therefore this review aims to provide a comprehensive summary of the importance of pretreatment of FW with respect to FW management by anaerobic digestion (AD) and dark fermentation (DF). It also reviews the existing knowledge gaps and future research perspectives for better integration of FW pretreatments for AD and DF, which should include (i) the preservation of carbon mass through freeze and thaw, or drying; and (ii) improve the carbon accessibility through particle size reduction and thermal pretreatments for methane/hydrogen recovery
This work concerns the investigation of the sequential production of lactic acid (LA) and biogas from food waste (FW). LA was produced from FW using a Streptococcus sp. strain via simultaneous saccharification and fermentation (SSF), and separate enzymatic hydrolysis and fermentation (SHF). Via SHF a yield of 0.33 gLA/gFW (productivity 3.38 gLA/L.h) and via SSF 0.29 gLA/gFW (productivity 2.08 gLA/L.h) was obtained. Fermentation residues and FW underwent anaerobic digestion (3 wt% TS). Biogas yields were 0.71, 0.74 and 0.90 Nm3/kgVS for FW and residues from SSF and SHF respectively. The innovation of the approach consists of considering the conversion of FW into two different high value products through a biorefinery chain, therefore making economically feasible LA production and valorising its fermentative residues. Finally, a mass balance involved three different process outlines with the aim to assess the amount of LA and biogas that may be generated within different scenarios.
The effects of pH, temperature and high organic loading rate (OLR) on lactic acid production from food waste without extra inoculum addition were investigated in this study. Using batch experiments, the results showed that although the hydrolysis rate increased with pH adjustment, the lactic acid concentration and productivity were highest at pH 6. High temperatures were suitable for solubilization but seriously restricted the acidification processes. The highest lactic acid yield (0.46g/g-TS) and productivity (278.1mg/Lh) were obtained at 37°C and pH 6. In addition, the lactic acid concentration gradually increased with the increase in OLR, and the semi-continuous reactor could be stably operated at an OLR of 18g-TS/Ld. However, system instability, low lactic acid yield and a decrease in VS removal were noticed at high OLRs (22g-TS/Ld). The concentrations of volatile fatty acids (VFAs) in the fermentation mixture were relatively low but slightly increased with OLR, and acetate was the predominant VFA component. Using high-throughput pyrosequencing, Lactobacillus from the raw food waste was found to selectively accumulate and become dominant in the semi-continuous reactor.
Foaming is one of the major operational problems in biogas plants, and dealing with foaming incidents is still based on empirical practices. Various types of antifoams are used arbitrarily to combat foaming in biogas plants, but without any scientific support this action can lead to serious deterioration of the methanogenic process. Many commercial antifoams are derivatives of fatty acids or oils. However, it is well known that lipids can induce foaming in manure based biogas plants. This study aimed to elucidate the effect of rapeseed oil and oleic acid on foam reduction and process performance in biogas reactors fed with protein or lipid rich substrates. The results showed that both antifoams efficiently suppressed foaming. Moreover rapeseed oil resulted in stimulation of the biogas production. Finally, it was reckoned that the chemical structure of lipids, and more specifically their carboxylic ends, is responsible for their foam promoting or foam counteracting behaviour. Thus, it was concluded that the fatty acids and oils could suppress foaming, while salt of fatty acids could generate foam.
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Composite organic waste was assessed for its physical, chemical and microbial suitability to serve as a substrate for the fermentative production of lactic acid. The biowaste studied was highly acidic (pH 4.3) and had high organic carbon content (45%). A clone library identified 90% of the bacterial community were lactic acid bacteria, mainly represented by Lactobacilli (70%). Cultivation using semiselective media identified Lactobacillus plantarum, Lactobacillus brevis and their closest relatives as the dominating taxa. PCR-DGGE using general bacterial and lactic acid bacterial specific primers resulted in little heterogeneity of microbial community. These data indicate that biowaste is a preferred habitat of lactic acid bacteria, suggesting that the unsterilized biowaste and its natural flora could be used in a fermentation process for lactic acid production. Such kind of biowaste application could be an alternative for current substrates and provide a modern, efficient and environmental friendly waste treatment technology.
Lactic acid bacteria (LAB) constitute a group of gram-positive bacteria united by a constellation of morphological, metabolic, and physiological characteristics. The general description of the bacteria included in the group is gram-positive, nonsporing, nonrespiring cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates. The LAB term is intimately associated with bacteria involved in food and feed fermentation, including related bacteria normally associated with the (healthy) mucosal surfaces of humans and animals. The boundaries of the group have been subject to some controversy, but historically the genera Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus form the core of the group. Taxonomic revisions of these genera and the description of new genera mean that LAB could, in their broad physiological definition, comprise around 20 genera. However, from a practical, food-technology point of view, the following genera are considered the principal LAB: Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, and Weissella. The genus Bifidobacterium, often considered in the same context as the genuine lactic acid bacteria and sharing some of their typical features, is phylogenetically unrelated and has a unique mode of sugar fermentation. The classification of lactic acid bacteria into different genera is largely based on morphology, mode of glucose fermentation, growth at different temperatures, configuration of the lactic acid produced, ability to grow at high salt concentrations, and acid or alkaline tolerance. Chemotaxonomic markers such as fatty acid composition and constituents of the cell wall are also used in classification. In addition, the present taxonomy relies partly on true phylogenetic relationships, which have been revealed by extensive work on determining rRNA sequences. Some of the newly described genera are most easily determined with oligonucleotide probes, polymerase chain reaction (PCR)–based technologies using these sequences, or direct sequencing of the 16S rRNA gene. Most genera in the group form phylogenetically distinct groups, but for some, in particular Lactobacillus and Pediococcus, the phylogenetic clusters do not correlate with the current classification based on phenotypic characters. New tools for classification and identification of LAB are currently replacing and/or complementing the traditional phenotype-based methodologies. The most promising for routine use are 16S rRNA gene sequencing, PCR-based fingerprinting techniques and soluble protein patterns.
Lactic acid, the most important hydroxycarboxylic acid, is now commercially produced by the fermentation of sugars present in biomass. In addition to its use in the synthesis of biodegradable polymers, lactic acid can be regarded as a feedstock for the green chemistry of the future. Different potentially useful chemicals such as pyruvic acid, acrylic acid, 1,2-propanediol, and lactate ester can be produced from lactic acid via chemical and biotechnological routes. Here, we reviewed the current status of the production of potentially valuable chemicals from lactic acid via biotechnological routes. Although some of the reactions described in this review article are still not applicable at current stage, due to their "greener" properties, biotechnological processes for the production of lactic acid derivatives might replace the chemical routes in the future.
Bioabsorbable polymers are considered a suitable alternative to the improvement and development of numerous applications in medicine. Poly-lactic acid (PLA,) is one of the most promising biopolymers due to the fact that the monomers may produced from non toxic renewable feedstock as well as is naturally occurring organic acid. Lactic acid can be made by fermentation of sugars obtained from renewable resources as such sugarcane. Therefore, PLA is an eco-friendly product with better features for use in the human body (nontoxicity). Lactic acid polymers can be synthesized by different processes so as to obtain products with an ample variety of chemical and mechanical properties. Due to their excellent biocompatibility and mechanical properties, PLA and their copolymers are becoming widely used in tissue engineering for function restoration of impaired tissues. In order to maximize the benefits of its use, it is necessary to understand the relationship between PLA material properties, the manufacturing process and the final product with desired characteristics. In this paper, the lactic acid production by fermentation and the polymer synthesis such biomaterial are reviewed. The paper intends to contribute to the critical knowledge and development of suitable use of PLA for biomedical applications.
The species Lactobacillus delbrueckii consists at present of three subspecies, delbrueckii, lactis and bulgaricus, showing a high level of DNA-DNA hybridization similarity but presenting markedly different traits related to distinct ecological adaptation. The internal genetic heterogeneity of the bacterial species L. delbrueckii was analyzed. Phenotypic and several genetic traits were investigated for 61 strains belonging to this species. These included 16S rDNA sequence mutations, expression of beta-galactosidase and of the cell wall-anchored protease, the characterization of the lactose operon locus and of the sequence of lacR gene, galactose metabolism, and the distribution of insertion sequences. The high genetic heterogeneity of taxa was confirmed by every trait investigated: the lac operon was completely deleted in the subsp. delbrueckii, different mutation events in the repressor gene of the operon led to a constitutive expression of lacZ in the subsp. bulgaricus. Structural differences in the same genetic locus were probably due to the presence of different IS elements in the flanking regions. The different expression of the cell wall-anchored protease, constitutive in the subsp. bulgaricus, inducible in the subsp. lactis, and absent in the subsp. delbrueckii was also a consequence of mutations at the gene level. The galT gene for galactose metabolism was found only in the subsp. lactis, while no specific amplification product was detected in the other two subspecies. All these data, together with the absence of a specific IS element, ISL6, from the major number of strains belonging to the subsp. bulgaricus, confirmed a deep internal heterogeneity among the three subspecies. Moreover, this evidence and the directional mutations found in the 16S rDNA sequences suggested that, of the three subspecies, L. delbrueckii subsp. lactis is the taxon closer to the ancestor. Limitations of the current prokaryotic species definition were also discussed, based on presented evidences. Our results indicate the need for an accurate investigation of internal heterogeneity of bacterial species. This study has consequences on the prokaryotic species concept, since genomic flexibility of prokaryotes collides with a stable classification, necessary from a scientific and applied point of view.
A number of Lactobacillus species, Bifidobacterium sp, Saccharomyces boulardii, and some other microbes have been proposed as and are used as probiotic strains, i.e. live microorganisms as food supplement in order to benefit health. The health claims range from rather vague as regulation of bowel activity and increasing of well-being to more specific, such as exerting antagonistic effect on the gastroenteric pathogens Clostridium difficile, Campylobacter jejuni, Helicobacter pylori and rotavirus, neutralising food mutagens produced in colon, shifting the immune response towards a Th2 response, and thereby alleviating allergic reactions, and lowering serum cholesterol (Tannock, 2002). Unfortunately, most publications are case reports, uncontrolled studies in humans, or reports of animal or in vitro studies. Whether or not the probiotic strains employed shall be of human origin is a matter of debate but this is not a matter of concern, as long as the strains can be shown to survive the transport in the human gastrointestinal (GI) tract and to colonise the human large intestine. This includes survival in the stressful environment of the stomach - acidic pH and bile - with induction of new genes encoding a number of stress proteins. Since the availability of antioxidants decreases rostrally in the GI tract production of antioxidants by colonic bacteria provides a beneficial effect in scavenging free radicals. LAB strains commonly produce antimicrobial substance(s) with activity against the homologous strain, but LAB strains also often produce microbicidal substances with effect against gastric and intestinal pathogens and other microbes, or compete for cell surface and mucin binding sites. This could be the mechanism behind reports that some probiotic strains inhibit or decrease translocation of bacteria from the gut to the liver. A protective effect against cancer development can be ascribed to binding of mutagens by intestinal bacteria, reduction of the enzymes beta-glucuronidase and beta-glucosidase, and deconjugation of bile acids, or merely by enhancing the immune system of the host. The latter has attracted considerable interest, and LAB have been tested in several clinical trials in allergic diseases. Characteristics ascribed to a probiotic strain are in general strain specific, and individual strains have to be tested for each property. Survival of strains during production, packing and storage of a viable cell mass has to be tested and declared.
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