Inhibition Of Polyphenol Oxidase Research Articles

Effects of aqueous chlorine dioxide treatment on polyphenol oxidases from Golden Delicious apple

Effects of chlorine dioxide (ClO 2) treatment on the activity and characteristics of polyphenol oxidase (PPO) in Golden Delicious apples were studied. The treatment with 50 mg/l ClO 2 for 1 h did not affect some characteristics of the PPO, including its optimum pH value (5.0) and temperature (40 °C) as well as the maximum absorption wavelength (412 nm) of the final products. With increasing ClO 2 concentrations from 0 to 100 mg/l, the V max ′ value reduced and K m ′ value changed irregularly. When the concentration of ClO 2 increased from 0 to 60 mg/l, residual PPO activities significantly decreased, showing a negative linear-correlation with ClO 2 concentration. For 10 and 50 mg/l ClO 2 treatments, partial inhibition of PPO was achieved within 0.5 h and the PPO activities did not significantly decrease after 0.5 h. The inhibition and inactivation of PPO by ClO 2 treatment were observed at processing temperatures (30 and 70 °C) and storing temperatures (20, 0–4, and −18 °C).

Gel electrophoresis of polyphenol oxidase with instant identification by in situ blotting

Polyphenol oxidase (PPO) or tyrosinase is an important and ubiquitous enzyme responsible for browning in plants and melanization in animals. The molecular size of the plant PPO is varied among the species and its activity can be enhanced by a variety of anionic detergents. In the present study, we developed a simple method for the first-step identification of PPO in fruit and vegetable extracts. First, 3 mm chromatographic paper was immersed in 0.5% (w/v) catechol solution as an immobilized PPO substrate. After running the extract with 10% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), one side of the glass plate was removed. The plate was immediately laid on top of the dried catechol-paper. A dark-brown band corresponding to PPO was visualized within 1 min and was further confirmed by a conventional Western blot using an antibody prepared against mushroom PPO. It also reveals that some vegetation (such as tomato, radish, and oriental melon) with low or no detectable activity in a conventional enzyme assay actually possessed marked levels of PPO activity when assessed by PAGE-blot. We propose that an inhibitor is associated with PPO in some plants; the inhibitor, however, is dissociated during the electrophoresis. Therefore, in addition to identify the molecular form of PPO, the present technique may explore the existence of PPO inhibitor(s) in plants. The detail of the method with respect to its relevance for searching a natural PPO inhibitor is described and discussed.

(65) Jasmonate-induced Changes in Polyphenol Oxidase, Peroxidase, and Proteinase Inhibitors in Horticultural Species

Jasmonates are a class of plant hormones involved in plant defense and stress responses. For example, jasmonate-induced defense responses in Lycopersicon esculentum include increases in activity of proteinase inhibitors, polyphenol oxidases, and peroxidases. As part of our efforts to reduce or control greenhouse pest infestations, we hypothesized that methyl jasmonate (MeJA) could induce these biochemical changes in common greenhouse crops. We studied Impatiens wallerana `Super Elfin Pink', L. esculentum `Big Boy', Petunia ×hybrida `Bravo Lavendar', Viola ×wittrockiana `Imperial Beaconsfield', Coleus ×hybridus `Wizard Jade', Nicotiana alata `Saratoga Lime', Pelargonium ×hortorum `Pinto Pink', and Tagetes erecta `Antigua Primrose'. Polyphenol oxidase and peroxidase activity was studied in the first four species, and proteinase inhibitors were studied in all eight. We sprayed plants with 0, 5 × 10-6, or 10-4 molar MeJA and made measurements after 24 hours. We detected a small increase in polyphenol oxidase activity of plants treated with 10-4 molar MeJA; 5 × 10-6 molar had no effect, and L. esculentum had the highest polyphenol oxidase activity. Peroxidase activity was not affected by MeJA. I. wallerana had the highest peroxidase activity, L. esculentum and V. ×wittrockiana had the lowest. 5 × 10-6 molar MeJA increased proteinase inhibitor activity in most species, and 10-4 molar increased activity in every species except P. ×hortorum.

Inhibition of Browning on Fresh-cut Pear Wedges by Natural Compounds

ABSTRACT: Mechanical operations such as peeling and cutting during minimal processing involve enzymatic browning of fruit tissue. The objective of this work was to evaluate the individual and combined effects of N-acetyl-L-cysteine, reduced glutathione, ascorbic acid, and 4-hexylresorcinol to control pear browning. Browning of fresh-cut pears was prevented by a minimum concentration of 0.75% N-acetyl-L-cysteine up to 28 d at 4°C. Reduced glutathione treatments were also effective along the storage time although browning was observed after 21 d of storage with a dip of 0.75% reduced glutathione. However, ascorbic acid or 4-hexylresorcinol treatments did not seem to completely prevent browning of pear wedges throughout the storage period. An enhanced antibrowning effect was observed when combining both N-acetyl-L-cysteine and reduced glutathione, considering hue angle as color change index. Thus, hue angle reached maximum levels at 1.5% N-acetyl-L-cysteine (NAC) or 1.5% glutathione (GSH) and 1% NAC with 1% GSH for 28 d. Besides, N-acetyl-L-cysteine, reduced glutathione and 4-hexylresorcinol completely inhibited polyphenol oxidase activity as well as browning inhibitors slightly reduced firmness of fresh-cut pears.

Some kinetic properties of polyphenol oxidase from Thymbra spicata L. var. spicata

Polyphenol oxidase (PPO) of Thymbra ( Thymbra spicata L. var. spicata) was isolated by (NH 4) 2SO 4 precipitation and dialysis. A diphenolase from Thymbra plant, active against 4-methylcatechol, catechol and pyrogallol was characterized in detail in terms of pH and temperature optima, stability, kinetic parameters and inhibition behaviour towards some general PPO inhibitors. 4-Methylcatechol was the most suitable substrate, due to the lowest K m and the biggest V max/ K m values, followed by catechol and pyrogallol. The Thymbra PPO had maximum activity at pH 5.0, 7.0 and 8.0 with 4-methylcatechol, catechol and pyrogallol substrates, respectively. The optimum temperature of activity for Thymbra PPO was 30, 40 and 50 °C for 4-methylcatechol, catechol and pyrogallol substrates, respectively. It was found that optimum temperature and pH were substrate-dependent studied. The enzyme activity decreased due to heat denaturation of the enzyme with increasing temperature and inactivation time. Inhibition of Thymbra PPO was investigated with inhibitors such as l-cysteine and glutathione using 4-methylcatechol, catechol and pyrogallol as substrates. It was found that l-cysteine was a more effective inhibitor than glutathione owing to lower K i. The type of inhibition depended on the origin of the PPO studied and also on the substrate used. Furthermore, the IC 50 values of inhibitors sudied on PPO were determined by means of activity percentage (I) diagrams.

Inhibition kinetics of polyphenol oxidase by glutamic acid

The inhibition of polyphenol oxidase (PPO) by glutamic acid was investigated. Application of different concentrations of glutamic acid to mushroom solution and Ocimum basilicum L. extract showed that glutamic acid appeared to be an effective browning inhibitor. Glutamic acid showed uncompetitive inhibition for mushroom and Ocimum basilicum L. polyphenol oxidases using 4-methylcatechol as a substrate, for mushroom PPO using catechol as a substrate and for Ocimum basilicum L. polyphenol oxidase using pyrogallol as a substrate; mixed-type inhibition for mushroom polyphenol oxidase using pyrogallol as a substrate; and non-competitive inhibition for Ocimum basilicum L. polyphenol oxidase using catechol as a substrate. Furthermore, sodium azide was used as an inhibitor for comparison with the inhibition potency of glutamic acid. It was found that glutamic acid was a more power inhibitor than sodium azide. The type of inhibition observed depended on the substrate, inhibitor and enzyme source used.

SUCROSE FATTY ACID COATING RETARDS PERICARP BROWNING OF LITCHI CV. ´HONG HUAY´

Pericarp browning of litchi fruit cv. 'Hong Huay' is a primary postharvest problem. The study determined the efficacy of sucrose fatty acid ester (SFE) coating in inhibiting browning. Fruit were dipped in 0.5-1.5% SFE or water (control) and stored at 5 C with 90-95% RH. Results showed that all SFE treatments retarded pericarp browning based on a subjective rating scale and objective L* and a* values. Optimum treatment appeared to be 1.0% SFE, delaying browning development by about 8 days relative to that of the control. It was most effective in reducing weight loss and maintaining higher water content. The effect was also partly due to the inhibition of polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) activity. All SFE treatments reduced PPO and PAL activity but did not affect total phenolics content.

Inhibition of Apple Polyphenol Oxidase Activity by Sodium Chlorite

Sodium chlorite (SC) was shown to have strong efficacy both as a sanitizer to reduce microbial growth on produce and as a browning inhibitor on fresh-cut apples in previous experiments. This study was undertaken to investigate the inhibitory effect of SC on polyphenol oxidase (PPO) and the associated mechanisms. The experiment showed that SC had a strong inhibition of apple PPO. The extent of inhibition was influenced by SC concentration and pH. Inhibition was most prominent at pH 4.5, at which approximately 30% of enzyme activity was lost in the presence of 10 mM SC, followed closely by that at pH 4.0 with a 26% reduction in PPO activity. The inhibition mode was determined using Dixon and Lineweaver-Burk plots, which established SC to be a mixed inhibitor of apple PPO for the oxidation of catechol. Preincubation of PPO with 8 mM SC for 8 min caused a maximum of 46% activity reduction compared to noninhibited control. However, preincubation of SC with catechol for 8 min resulted in no additional loss of PPO activity. These findings provide further evidence that the inhibition of PPO activity by SC is due to the inhibition of the enzyme itself rather than removal of the substrate.

Delineating the Role of Polyphenol Oxidase in the Darkening of Alkaline Wheat Noodles

This study evaluated the effects of inhibitors on polyphenol oxidase (PPO) activity, the effect of the PPO inhibitor tropolone on noodle darkening, and the correlation of PPO activity with darkening of alkaline noodles. The PPO inhibitors tropolone and salicylhydroxamic acid (each at 1 microM) reduced kernel PPO activity by approximately 50% in three hexaploid wheat cultivars but did not inhibit PPO activity in the two very low PPO cultivars, durum Langdon, and the synthetic hexaploid-derived ID580. Tropolone (100 microg/g flour) inhibited alkaline noodle darkening (deltaL*) by 13-25% in the low PPO wheat cultivar, ID377s, and by 39-54% in the high PPO wheat cultivar, Klasic. Alkaline noodle darkening among 502 wheat samples was correlated with kernel PPO activity (r = 0.64). Results substantiate the hypothesis that PPO plays a major role in darkening of alkaline noodles. However, results also indicate that substantial darkening would occur even at zero PPO activity, as measured in the kernel PPO assay. Therefore, darkening of alkaline noodles is probably due to the cultivar-specific level of PPO activity and the presence of at least one additional darkening mechanism. Further investigation is required to identify the phenolic discoloration agent(s) and to determine the potential roles of non-PPO discoloration mechanisms, both enzymatic and nonenzymatic, in wheat products.

Antioxidant and Possible Anti-Inflammatory Potential of Selected Medicinal Plants Prescribed in the Indian Traditional System of Medicine

The 50% alcohol extracts of Swertia chirayita. (Roxb. ex Flem) (Gentianaceae), Cedrus deodar. (Roxb. ex Lamb) (Pinaceae), Boerhavia diffusa. (Linn.) (Nyctaginaceae), Berberis aristata. (Linn.) (Berberidaceae), Withania somnifera. Dunal (Solanaceae), Pongamia glabra. (Vent) (Papilionoideae), Petrocarpus santalinus. (Linn.) (Papilionoideae), Tinospora cordifolia. (Willd) Miers (Menispermaceae), and Acrous calamus. (Linn.) (Araceae), were screened for antioxidant and possible anti-inflammatory potential. The evaluation of antioxidant potential was determined by performing 2,2-diphenyl-1-picryl hydrazine (DPPH˙) reduction assay, OH radical (OH˙) scavenging activity, estimation of vitamin C, total polyphenols, and inhibition of polyphenol oxidase (PPO) as a model oxidizing enzyme. To understand the possible anti-inflammatory potential of the selected plants, trypsin and β.-glucuronidase inhibition assays were carried out. All the plants under study were found to be effective scavengers of DPPH radicals. Among the tested plants, only Pongamia glabra, Petrocarpus santalinus, Tinospora cordifolia., and Acrous calamus. were found to possess OH radical scavenging activity. Appreciable amounts of vitamin C and phenolics were estimated from all the plant extracts under study. Except for Pongamia glabra., all the tested plants demonstrated significant PPO inhibitory activity. The plants under study were found to have moderate antiproteolytic activity toward trypsin-induced hydrolysis of bovine serum albumin. Except for Cedrus deodar. and Acrous calamus., none of the plant extracts showed β.-glucuronidase inhibitory potential. The results of the current study may be of use for standardization and validation of herbal drugs containing the above mentioned plants as one of the ingredients.

Enzymatic Method with Polyphenol Oxidase for the Determination of Cysteine and N-Acetylcysteine

Thiols, such as cysteine and N-acetylcysteine, are included in many pharmaceutical products for their mucolytic properties. The method described here uses mushroom polyphenol oxidase (PPO) to determine two thiols and consists of measuring the lag period in the formation of the product generated as PPO acts on o-diphenol in the presence of a thiol. In the experimental conditions, o-quinone is formed enzymatically and then reacts stoichiometrically with the thiol, originating the corresponding thiol-diphenol adduct, which does not absorb visible light. Once the thiol has been used up, the o-quinone can be observed in the medium. It must be borne in mind that the inhibition of PPO is practically null at low concentrations of thiol, and the only effect observed is the formation of the thiol-diphenol adduct. In the following, an exact kinetic method capable of rapidly and accurately assaying thiols with PPO and o-diphenol is optimized and is shown to be a straightforward way of calculating thiol concentration. The method has been successfully applied to the determination of cysteine in model solutions and of N-acetylcysteine in pharmaceutical products.

Diphenolases from Anoxybacillus kestanbolensis strains K1 and K4 T

Diphenolases from Anoxybacillus kestanbolensis strains K1 and K4T, highly active against 4-methylcatechol were characterized in terms of pH- and temperature-optima, pH- and temperature-stability, kinetic parameters, and inhibition/activation behaviour towards some general polyphenol oxidase (PPO) inhibitors and metal ions. The temperature-activity optima, for Anoxybacillus kestanbolensis K1 and K4T catecholases in the presence of 4-methylcatechol, were 80 and 70 °C, respectively. Although catecholase from A. kestanbolensis K4T lost no activity after a period of 1 h incubation at its optimum temperature, the enzyme pH from K1 was stimulated by keeping at 80 °C. Both of the enzymes possessed pH optima at 9.5, and the pH-stability profiles showed that cathecholases from both preparations retained their activities at alkaline pH values. Both A. kestanbolensis K1 and K4T catecholase activities were totally inhibited by addition of 0.01 mM sodium metabisulphite, ascorbic acid and l-cysteine. 1 mM Mn2+ increased the activities of A. kestanbolensis K1 and K4T catecholases by 6.4- and 5.3-fold, respectively. These results indicate that both A. kestanbolensis K1 and K4T strains possess thermo- and alkalostable catecholases.

Characterization and Purification of Polyphenol Oxidase from Artichoke (Cynara scolymus L.)

In this study, the polyphenol oxidase (PPO) of artichoke (Cynara scolymus L.) was first purified by a combination of (NH(4))(2)SO(4) precipitation, dialysis, and a Sepharose 4B-L-tyrosine-p-aminobenzoic acid affinity column. At the end of purification, 43-fold purification was achieved. The purified enzyme migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Polyacrylamide gel electrophoresis indicated that PPO had a 57 kDa molecular mass. Second, the contents of total phenolic and protein of artichoke head extracts were determined. The total phenolic content of artichoke head was determined spectrophotometrically according to the Folin-Ciocalteu procedure and was found to be 425 mg 100 g(-1) on a fresh weight basis. Protein content was determined according to Bradford method. Third, the effects of substrate specificity, pH, temperature, and heat inactivation were investigated on the activity of PPO purified from artichoke. The enzyme showed activity to 4-methylcatechol, pyrogallol, catechol, and L-dopa. No activity was detected toward L-tyrosine, resorsinol, and p-cresol. According to V(max)/K(m) values, 4-methylcatechol (1393 EU min(-1) mM(-1)) was the best substrate, followed by pyrogallol (1220 EU min(-1) mM(-1)), catechol (697 EU min(-1) mM(-1)), and L-dopa (102 EU min(-1) mM(-1)). The optimum pH values for PPO were 5.0, 8.0, and 7.0 using 4-methylcatechol, pyrogallol, and catechol as substrate, respectively. It was found that optimum temperatures were dependent on the substrates studied. The enzyme activity decreased due to heat denaturation of the enzyme with increasing temperature and inactivation time for 4-methylcatechol and pyrogallol substrates. However, all inactivation experiments for catechol showed that the activity of artichoke PPO increased with mild heating, reached a maximum, and then decreased with time. Finally, inhibition of artichoke PPO was investigated with inhibitors such as L-cysteine, EDTA, ascorbic acid, gallic acid, d,L-dithiothreitol, tropolone, glutathione, sodium azide, benzoic acid, salicylic acid, and 4-aminobenzoic acid using 4-methylcatechol, pyrogallol, and catechol as substrate. The presence of EDTA, 4-aminobenzoic acid, salicylic acid, gallic acid, and benzoic acid did not cause the inhibition of artichoke PPO. A competitive-type inhibition was obtained with sodium azide, L-cysteine, and d,L-dithiothreitol inhibitors using 4-methylcatechol as substrate; with L-cysteine, tropolone, d,L-dithiothreitol, ascorbic acid, and sodium azide inhibitors using pyrogallol as substrate; and with L-cysteine, tropolone, d,L-dithiotreitol, and ascorbic acid inhibitors using catechol as a substrate. A mixed-type inhibition was obtained with glutathione inhibitor using 4-methylcatechol as a substrate. A noncompetitive inhibition was obtained with tropolone and ascorbic acid inhibitors using 4-methylcatechol as substrate, with glutathione inhibitor using pyrogallol as substrate, and with glutathione and sodium azide inhibitors using catechol as substrate. From these results, it can be said that the most effective inhibitor for artichoke PPO is tropolone. Furthermore, it was found that the type of inhibition depended on the origin of the PPO studied and also on the substrate used.

Effect of coating and intermittent warming on enzymes, soluble pectin substances and ascorbic acid of Prunus persica (Cv. Zhonghuashoutao) during refrigerated storage

The effect of 1% chitosan coating + polyethylene (PE) package, 1% chitosan + 0.5% CaCl 2 coating + PEpackage, and 1% chitosan + 0.5% CaCl 2 coating + PEpackage + intermittent warming on the enzymes and quality of Zhonghuashoutao fruits ( Prunus persica) was studied during refrigerated storage (1 °C). The results showed that, compared to the control (CK) of water dip + PEpackage, all treatments had positive effectiveness on the inhibition of polyphenol oxidase, peroxidase (POD), ascorbic acid oxidases (ASA-POD) and polygalacturonase (PG) activities to some extent, and reduced the increase of soluble pectinefic substance. Results also showed that 1% chitosan + 0.5% CaCl 2 + PEpackage + intermittent warming treatment significantly inhibited ASA-POD and PG activities, kept vitamin C at a high level, and reduced fruit sensitivity to chilling injury at the later stage of storage.

Inhibition of polyphenoloxidase in mango puree with 4-hexylresorcinol, cysteine and ascorbic acid

Mango puree, at three pH (3.5, 4.0, or 4.4) was mixed with 4-hexylresorcinol (4-HR) (40, 60, or 80mg/kg), cysteine (Cys) (100, 200, or 300mg/kg), or ascorbic acid (AA) (250, 500, or 1000mg/kg) to assess their effect on polyphenoloxidase (PPO) activity. Combinations of 4-HR/Cys and 4-HR/AA at pH 3.5 were also studied. PPO activity was analysed spectrophotometrically at 30°C. Mango purees were stored for at least three weeks at 3±1°C. L*, a*, and b* color parameters were analysed to evaluate mango color stability. The PPO activity in fresh mango puree at pH 3.5, 4.0, and 4.4 exhibited 11.7, 23.1, and 259.2 PPO activity units, respectively. This means there was a reduction in 95.5 and 91.1% of PPO activity for pH 3.5 and 4.0 respectively. No significant differences (*P>0.05) were observed for PPO activity among anti-browning agents and concentrations used separately, but PPO activity at pH 4.4 was significantly different (*P<0.05). All concentrations at of AA and 300mg/kg of Cys at pH 3.5 and 4.0 exhibited less darkening during storage. No significant differences in PPO activity were observed for combinations of AA or 4-HR. The darkening effect of puree was slowed down as Cys and AA concentrations were increased in combination with 4-HR.

Influence of selenium on oxidoreductive enzymes activity in soil and in plants

The aim of this greenhouse experiment was the assessment of the influence of H 2SeO 3 at soil concentrations of 0.05, 0.15 and 0.45 mmol kg −1, on the activity of selected oxidoreductive enzymes in wheat ( Triticum aestivum). The wheat plants were grown in 2 dm 3 pots filled with dust-silt black soil of pH 7.7. Applied H 2SeO 3 caused activation of plant nitrate reductase at all concentrations, but activation of plant polyphenol oxidase at only two lower concentrations. The highest concentration caused inhibition of polyphenol oxidase and peroxidase. Plant catalase activity decreased under the influence of 0.15 and 0.45 mmol kg −1 concentration. After the final analysis Se was quantified in plants and soil. The amounts in plants were: control (unamended soil) 1.95 mg kg −1; I dose (0.05 mmol kg −1) 18.27 mg kg −1; II dose (0.15 mmol kg −1) 33.20 mg kg −1 and III dose (0.45 mmol kg −1) 38.37 mg kg −1, in soil: 0.265 mg kg −1; 3.61 mg kg −1; 10.53 mg kg −1; 30.53 mg kg −1; respectively. Simultaneously, a laboratory experiment was performed, where the activity of soil catalase and peroxidase were tested after 1, 3, 7, 14, 28, 56, and 112 days after Se treatment. Peroxidase activity in soil decreased with increasing Se content, over the whole experiment. The lowest dose of Se caused activation a significant 10% increase in catalase activity, but the influence of others doses was unclear.

Characterization of polyphenol oxidase from plants

Polyphenol oxidase (PPO) which can mediate browning reaction is a bifunctional copper-containing enzyme encoded by plant nucleolus gene. It usually leads to excessive browning reaction which reduces the commercial profits of fruits and vegetables. In this paper, PPO genes and enzymes in plants are characterized systematically, and the latest progress is reviewed. Some clonings of PPOs genes are reported; the specific temporal and spatial expression pattern of PPOs genes is described; the model of the structure of the precursor form of catechol oxidase is introduced; the possible functions of PPOs in defending against pathogen, wounding, surrounding stress and other inducing factors are demonstrated; the induction and activation of latent PPOs in some plants is elucidated; the scheme of browning inhibition by L-cysteine is clarified; the mechanism of suicide inhibition of latent PPO and kinetic synergism are established. Furthermore, the area for future study is also discussed.

Purification of mulberry ( Morus alba L.) polyphenol oxidase by affinity chromatography and investigation of its kinetic and electrophoretic properties

Polyphenol oxidase (PPO) was isolated from mulberry ( Morus alba L.) fruit using a Sepharose 4B- l-tyrosine- p-amino benzoic acid affinity column. The purified enzyme was migrated as a single band on native and SDS–poliacrylamide gel electrophoresis. The molecular weight of the purified enzyme was estimated to be 65 kDa. Optimum PPO activity as a function of pH and temperature was determined using catechol, 4-methyl catechol and pyrogallol as substrates. The optimum pH and temperatures values of mulberry PPO for the used three substrates ranged between the pH 4.5–8.0 and 20–45 °C. At the optimum pH and temperature, the K M and V Max values of mulberry PPO towards catechol, 4-methyl catechol and pyrogallol were determined by Lineweaver–Burk method. The values V Max/ K M showed that mulberry has the greatest reactivity towards pyrogallol among the substrates used. On the other hand mulberry PPO showed no activity toward the monophenols, p-cresol and l-tyrosine, suggesting the absence of monophenolase (cresolase) activity. Beside the classical PPO inhibitors, for the first time the inhibitory effect of some sulfonamide compounds on the mulberry PPO activities was also tested. Sulfonamide compounds exhibited considerable inhibition on mulberry PPO enzyme.

Effect of Chemical Treatment with Citric Acid or Ozonated Water on Microbial Growth and Polyphenoloxidase Activity in Lettuce and Cabbage

Effects of chemical treatment with a citric acid solution or ozonated water on microbiological changes in lettuce and cabbage during storage were studied. Fresh lettuce and cabbage samples were cut into small pieces and treated by soaking in either ozonated water or a citric acid solution. After treatment, populations of total bacteria, yeast and mold, and E. coli were determined. Numbers of microorganisms increased during storage, but ozonated water and citric acid treatments retarded the increase in microbial growth. Among treatments, 1% citric acid treatment was the most effective in terms of microbiological change and inhibition of polyphenoloxidase (PPO). For lettuce, citric acid treatment decreased the microbial growth overall by 1.5 log CFU/g and inhibited the PPO activity by 80%. These results indicate that chemical-treated lettuce and cabbage retained a better quality than those of the control during storage.

Glutathione and Cinnamic Acid: Natural Dietary Components Used in Preventing the Process of Browning by Inhibition of Polyphenol Oxidase in Apple Juice

Consumer demands for ‘freshness’ in processed foods has been given increasing attention by food processing industries by searching for minimally processed products. Polyphenol Oxidase (PPO) mediated browning is a major cause of undesirable flavors and nutritional losses in fruit juices. Here the anti-browning efficiency of glutathione (GSH, reduced form) and cinnamic acid (CA) in apple juice is evaluated. It was observed that the rate of the browning reaction could be efficiently delayed using GSH and CA, which act as inhibitors of PPO. Kinetic studies confirm that GSH and CA are non-competitive and competitive inhibitors of PPO respectively.