Content uploaded by Roberto Massini
Author content
All content in this area was uploaded by Roberto Massini on May 06, 2015
Content may be subject to copyright.
A preview of the PDF is not available
Preventing enzymic browning of potato by microwave blanching
Abstract
Samples of potato slices and cubes, cultivar Primura, were blanched by dipping them in boiling water and hypertonic corn syrup solution, by microwaves and microwaves upon water immersion, with or without sodium chloride and/or calcium chloride. Treatments were performed at 98 degreesC, 100 degreesC and 850 Watts, respectively, for different times. Some physical characteristics (colour and firmness of samples) as well as mass and water transfers were evaluated. The results showed that the samples of potato cubes put in water and blanched by microwaves were the most stable in terms of colour but the least consistent, probably because of the accelerated gelatinization of potato starch. The firmness of product blanched by microwave was improved by using a calcium chloride and sodium chloride aqueous solution as blanching bath.
... However, the most efficient way to control this problem is the combination of physical and chemical methods, by avoiding the use of more severe individual treatments, which could harm the appearance and texture of the processed food. Technological processing, including microwave blanching either alone or combined with chemical anti-browning agents [13][14][15][16]; or natural anti-browning agents like pineapple juice [17], onion juice [18], onion oil [19], onion extracts [20], onion by-products (residues and surpluses) is also commonly used [21]. ...
... This shows that a combination of blanching and chemically treatment was the most effective for inhibition of PPO in this variant of Dioscorea rotundata. A similar observation has been reported in which a combination of physical and chemical treatments was proven to be most effective in the inhibition of PPO on lettuce [13]. The results obtained are also in line with a study where it was observed that PPO from Dioscorea cayenensis-rotundata cv. ...
Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a
negative way. The objective of this present study was to examine the activity of polyphenol oxidase in Dioscorea rotundata. Var.
laasirin and the efficiency of heat and chemical treatments in inhibiting this enzyme. Crude Polyphenol Oxidase (PPO) of Dioscorea
rotundata.Var. Laasirin was isolated and the kinetics studied using the lineweaver-burk plot. The activity of the enzyme was
evaluated using spectrophotomeric method. Yam PPO catalyzes oxidation of various substrates with catechol being the most readily
oxidized substrate. The Michaelis-Menten constant (Km) and maximum reaction velocity (Vmax) for yam PPO were 0.00037 and
0.3125 respectively. Inhibition data showed that the enzyme had least activity (71.70) when blanched at 95 °C for 7 mins with
chemical treatment involving a combination of 0.5% Sodium metabisulphite (Food grade) and 0.5% Ascorbic acid (Food grade). The
activity was highest (83.02) when it was blanched at 95 °C for 7 mins. This study has shown that it is possible to inhibit polyphenol
oxidase activity in white yam using the chemical pretreatments and processing conditions described in this study for possible
adoption in the production of packaged frozen yam chips by food industries.
... It is important to emphasize that this study was conducted with a natural agent which meets the needs of the consumer. A similar observation was obtained by Severini et al. [24]. The activity of the POD as evaluated by Bahçeci et al. [25] found blanching green beans at 95°C for 2 min resulted in 90% inactivation of POD. ...
Aim: To prevent enzymatic browning during the freezing of yam slices of the Kponan variety (Dioscorea cayenensis-rotundata). Study Design: The experimental set-up was of a completely randomized design. Place and Duration of Study: Department of Food Science and Technology, Food Biochemistry and Tropical Products Technology Laboratory (BATPTL), University of Nangui Abrogoua, Abidjan, Côte d’Ivoire, between August and December 2018. Methodology: For this purpose, yam slices were either pretreated with a natural agent (lemon juice solution at different pH) or pretreated and blanched (85 °C for 2 min) and then packed in plastic bags and kept in the freezer at -18°C over a period of 4 weeks. Polyphenoloxidase and Peroxidase activities, Dry matter, rate of browning and sensory attributes of yam slices were determined. Results: The results showed a decrease in polyphenoloxidase and peroxidase activities regardless of the treatment. The largest decreases in activity were observed in yam slices that were both pretreated and blanched compared to the control (about 53.49% decrease in the specific activity of the PPOs and 51.46% of POD). The combination of pretreatment and blanching also resulted in lower dry matter yam slices compared to pretreated slices only. After 1 month of storage in the freezer, the lower rates of loss (browning) were recorded for the slices of yams that were both pretreated and blanched compared to the other methods which had very high losses. The pretreated and blanched slices had high dry matter content. The sensory profile of slices processed by the combined technique after one month of freezing had a good appreciation for all sensory characteristics of yam. Conclusion: In order to have a good product, the combined method is recommended for better freezer storage of yam slices.
... Physical treatments such as heat, dehydration, irradiation and high pressure are another strategy to minimize browning. Blanching treatments by steam, hot water, acid/salt water solutions and microwave are also largely used (86,87). However, to balance the degree of inactivation of PPOs and the impact on the quality of end-products, time and temperature of blanching should be carefully set up (88). ...
Polyphenol oxidase, a copper-containing metalloprotein, catalyzes the oxidation of phenolic compounds to quinones, which produce brown pigments in wounded tissues. This enzymatic mechanism causes post-harvest losses and mainly affects tropical fruits and vegetables. The enzymes purified form different plant sources showed dif ferences in the biochemical properties. The PPO protein structure has been elucidated and reported in few plants. The active site of the enzyme undergoes transitions among met-, oxy-, and deoxy-forms in a cyclic manner for catalysis. In this article, biochemical characteristics of polyphenol oxidase from different plants are reviewed. Biochemical and molecular characterization of the polyphenol oxidase could help to develop or to choose more effective methods for controlling browning of fruits, vegetables and its products. © 2018, Indian Society of Agricultural Biochemists. All rights reserved.
... Physical treatments such as heat, dehydration, irradiation and high pressure are another strategy to minimize browning [77]. Blanching treatments by steam, hot water, acid/salt water solutions, and microwave are also largely used [86][87][88][89][90][91][92][93]. However, to balance the degree of inactivation of PPOs and the impact on the quality of end-products, time and temperature of blanching should be carefully set up [94]. ...
Enzymatic browning is a colour reaction occurring in plants, including cereals, fruit and horticultural crops, due to oxidation during postharvest processing and storage. This has a negative impact on the colour, flavour, nutritional properties and shelf life of food products. Browning is usually caused by polyphenol oxidases (PPOs), following cell damage caused by senescence, wounding and the attack of pests and pathogens. Several studies indicated that PPOs play a role in plant immunity, and emerging evidence suggested that PPOs might also be involved in other physiological processes. Genomic investigations ultimately led to the isolation of PPO homologs in several crops, which will be possibly characterized at the functional level in the near future. Here, focusing on the botanic families of Poaceae and Solanaceae, we provide an overview on available scientific literature on PPOs, resulting in useful information on biochemical, physiological and genetic aspects.
... The most efficient way to control this problem is the combination of physical and chemical methods, by avoiding the use of more severe individual treatments, which could harm the appearance and texture of vegetables. Technological processing, including microwave blanching either alone or combined with chemical anti-browning agents (Severini et al. 2001, Premakumar and Khurduya 2002, Yadav et al. 2008, Guan and Fan 2010; CO 2 treatments (Rocha and Morais 2001, Kaaber et al. 2002, Valverde et al. 2010); pretreatments employing sodium or calcium chloride and lactic acid followed by conventional blanching (Severini et al. 2003); combination of sodium chlorite and calcium propionate (Guan and Fan 2010); high pressure treatments combined with thermal treatments and chemical anti-browning agents such as ascorbic acid (Prestamo et al. 2000, Ballestra et al. 2002 or natural anti-browning agents like pineapple juice (Perera et al. 2010); and UV-C light treatment of fresh-cut vegetables under nonthermal conditions (Manzocco et al. 2009) have been employed to prevent enzymatic browning in foods. The use of edible coating from whey protein isolate-beeswax (Perez-Gago et al. 2003); edible coatings enriched with natural plant extracts (Ponce et al. 2008); oxygen-controlled atmospheres (Jacxsens et al. 2001, Soliva-Fortuny et al. 2001, Duan et al. 2009), and the use of active films (Endo et al. 2008) seem to improve the shelf life of foods by inhibition of PPO. ...
Browning is one of the most important reactions taking
place during food processing and storage. Both, enzymatic and
nonenzymatic browning can affect the quality of food in either
positive or negative ways, depending on the type of food. Special
attention has been paid in this chapter to chemistry of the reaction.
During enzymatic browning phenolic compounds are oxidized
to quinones by polyphenol oxidase, this reaction being of particular
importance in fruits, vegetables, and seafoods. Nonenzymatic
browning is referred to the Maillard reaction (MR), when it takes
place between free amino groups from amino acids, peptides, or
proteins and the carbonyl group of reducing sugars. Ascorbic acid,
its oxidation products and oxidized lipids can also react via MR.
It has been also described that aminophospholipids and reducing
carbohydrates can interact by MR. Food browning can be also due
degradation of carbohydrates also called caramelization reaction
and it is hereby discussed.
Interest in the application of microwave heating (MW) to the food industries began in the years following the end of the Second World War, as a continuation of the investigations that had given place to the development of the radar (Decareau, 1985). The first patent was registered in 1949 by Percy Spencer for the production of popcorn. Nevertheless, technological reasons and the high costs of investment stopped the development of applications until the beginning of the 1960s. Even then, the high price of industrial facilities limited the development to domestic equipment and the catering industry (Decareau, 1985).
The market demand for minimally processed fruits and vegetables has undergone an important rise during recent years because of busy lifestyles, increasing purchasing power, and increasingly health-conscious consumers. Minimal processing for vegetables has been defined as a combination of procedures, such as washing, sorting, trimming, peeling, and slicing or chopping, that do not affect the fresh quality of the food. Furthermore, it would seem that the cut provokes a stress reaction of increased enzyme production. There are numerous works in literature concerning enzyme alteration in fresh-cut vegetables. In particular, in this review we selected and described the enzymes relating to the main alteration of fresh cut productions: softening (PME, PG) and browning (PPO, PAL).
Phenolic compounds, together with ascorbic acid and some other bioactive compounds, have been linked with the health-promoting effects of grapes, mainly due to their antioxidant capacity. Despite the fact that the different processes carried out to obtain fruit products could affect their bioactive content, the process applied in this work to obtain raisins and canned grapes have not shown undesirable effects. In fact, the use of microwaves instead of hot air not only promotes the antioxidant capacity of raisins, but also the antioxidant capacity of the product.
Response surface methodology was used to investigate variables affecting the firmness of blanched potato slices such as type of blanching, time of treatment, NaCl or CaCl2 concentrations and lactic acid concentration. Results showed that the mathematical models were able to provide a good estimate of the effects of individual and interactive factors on the retention of firmness of processed potato. The best results were obtained with microwave blanching of slices dipped in calcium chloride-containing solution. In addition to firmness analysis, weight loss, moisture and starch crystallinity levels were used to determine blanching treatment effectiveness.
Enzyme catalysed reactions can occur at significant rates at low temperatures, thus exerting a major control on the quality of frozen foods. The temperature-concentration effect in partially frozen systems can make enzyme reactions controlled by diffusion and thus rate limited by viscosity according to the Stokes–Einstein relation. Polyphenoloxidase (PPO) activity in sucrose, glycerol and fructose water media and (POD) activity in fructose and glycerol water media, were assayed spectrophotometrically from 20°C to −30°C. The media have at equal sub-freezing temperature marked differences in viscosities and others physical properties. For both enzymes, the activity data showed similar dependence on temperature and, above freezing, on the concentration of the media. A relation with the viscosity of the media at equal sub-freezing temperature was not evident. POD activity showed a “break” between −10°C and −20°C, suggesting a reversible conformational change. The temperature dependence of PPO rate constants were well described by both the Williams–Landel–Ferry (r2=0.998) and the Arrhenius (r2=0.985) models. A hypothesis for the non conformity of the measured kinetics with the theoretical model is that in the temperature range considered the reactions are still activation controlled or in a transition zone, and should become diffusion limited only at lower temperatures and higher viscosities.
Fruit pieces of some species have been processed to be used as ingredients in various food systems, either by partial dehydration alone or by osmosis and partial dehydration, to achieve different levels of water activity and solids contents in the final products.The relationships existing among processing, phase composition after processing and functional properties of the products have been assessed within a useful range of water content and water activity.The functional properties are expressed as diagrams relating the phase composition (soluble solids, insoluble solids and water) to the range of consistencies obtainable at various water activities. These diagrams provide a useful tool for preparing fruit ingredients suitable for specific food systems.
Reflectance procedures were developed to measure the extent of enzymatic browning at cut surfaces and in the raw juice of apple and pear fruits. Reflectance L and a measurements, made at transversely cut surfaces of plugs bored from fruit halves, were linear or bilinear with log time and related to the extent of browning in six apple cultivars. With apple and pear juices, tristimulus values changed linearly with time in samples undergoing browning. Differences between initial and final tristimulus values were better indices of browning than the slopes of time curves. The suitability of these procedures for evaluating the effectiveness of browning inhibitors was demonstrated with SO2 and ascorbic acid treatments.
The effect of variety, climatic factors and nutritional factors on the enzymic browning of cut potatoes has been investigated. The major factor determining the rate of enzymic browning appears to be the concentration of tyrosine in the tuber. There was no direct correlation between the activity of the phenolase enzyme or the amount of chlorogenic acid and the rate of browning. The level of tyrosine in a potato was shown to be determined by genetic, climatic and, to a lesser extent, by nutritional factors. Of the climatic factors, rainfall, or the moisture available to the plant, appeared to be the most important.
Peroxidase was regenerated in samples of peas that had been blanched just sufficiently to destroy the original peroxidase activity. The regeneration occurred after a few months in peas stored at −18° C, or within a few hours in thawed peas held at room temperature. The maximum activity regenerated was about 4% of the original activity. No regeneration occurred in peas given substantially more heat treatment than was needed for inactivation. Peroxidase regeneration during frozen storage, or after thawing, did not affect the quality of peas.
Feasibility of lye digestion to remove surface tissues from peeled potatoes prior to treatment with browning inhibitors to extend shelf-life was investigated. Russet and round-white potatoes were digested in 14–20% NaOH at 35–55°C for 1–13 min. After removal of digested tissue, tubers were treated with ascorbic acid-based browning inhibitor. Browning was measured by tristimulus calorimetry. Digestion extended shelf-life of high pressure steam- and abrasion-peeled potatoes to 13–15 days at 4°C, compared to 3–11 days for undigested controls. Digestion resulted in weight losses of 12–26%, depending on treatment conditions. Lye digestion in conjunction with conventional browning inhibitors represents a viable alternative to sulfiting pre-peeled potatoes.