• Horticultural Science & Technology
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• v.29 no.3
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• pp.255-259
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• 2011

Polyphenol oxidases (PPO) are copper-containing enzymes responsible for tissue browning in fruits and vegetables including potato, apple and pears. Although these enzymes have been studied for many years, their physiological roles in plants are not yet clear. Therefore, these enzymes need to be purified to characterize further from potato tubers. The classical methods used for the purification of PPO involve several steps. So in this study, we developed a one-step chromatography process for the potato tuber PPO purification. After removal of salts from dissolved ammonium sulfate precipitates of potato tuber extracts using Sephadex-G50 gel filtration, affinity chromatography was carried out on NHS-activated Sepharose 4B using p-aminobenzoic acid as a ligand. The purified enzyme was confirmed by silver staining and a zymogram. The optimum temperature and pH for the purified potato tuber PPO were $15^{\circ}C$ and pH 6.0, respectively. The results obtained in the present study will aid to evaluate PPO from various fruits and vegetables.

• Korean Journal of Pharmacognosy
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• v.20 no.2
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• pp.101-109
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• 1989

Purification of polyphenol oxidase(PPO) from Korean native tobacco variety leaves was carried out through the procedure of acetone preciptation, ammonium sulfate fractionation, and Sephadex G-150 gel filtration, resulting in a 84-fold increase in specific activity. The enzyme was stable in a range of pH 7.5 to 8.0 with an optimum of pH 7.5. The optimum temperature for the enzymic reaction was about $60^{\circ}$. It was thermostable with a half-life equal to 20 min at $70^{\circ}$. Km values for (+)-catechin and pyrogallol were $1.6{\times}10^{-3}$ and $0.5{\times}10^{-3}M$, respectively. It possesses high catecholase activity but little or no cresolase activity. Lineweaver-Burk analysis of inhibition data revealed that the inhibition of (+)-catechin oxidation by potassium cyanide, 4-nitrocatechol, cystein and 2-mercaptoethanol was competitive with Ki values of $1.1{\times}10^{-6}$, $1.8{\times}10^{-6}$, $8.9{\times}10^{-6}$ and $1.3{\times}10^{-5}$, respectively.

• Journal of The Korean Society of Grassland and Forage Science
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• v.34 no.1
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• pp.15-20
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• 2014

To investigate lignification process and its physiological significance under water-deficit condition, the responses of peroxidases, polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) in relation to leaf water status to the short term of water deficit treatment in the leaves with different maturities in forage rape were measured. The significant decrease in relative water content (RWC) and leaf osmotic potential (${\Psi}{\pi}$) were apparent after 5 d of water-deficit treatment. The activity of guaiacol peroxidase (GPOD), ascorbate peroxidase (APOD), coniferyl alcohol peroxidase (CPOD), and syringaldazine peroxidase (SPOD) was depressed especially in middle and old leaves when compared with that of control leaves. On the other hand, in young leaves, a significant increase in CPOD (+34%) and SPOD (+24%) activity as affected by water-deficit treatment was apparent. The activation of PAL and PPO was observed in middle and old leaves for PAL and in young and middle leaves for PPO. These results suggest that peroxidases in middle and old leaves did not involve in lignification under mild water-deficit stress, whereas CPOD and SPOD in young leaves participate in lignification by a coordination with PAL and PPO to incorporate phenol and lignin into the cell walls.

• YAKHAK HOEJI
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• v.45 no.4
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• pp.387-396
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• 2001

The effects of ascorbic acid, thiols such as cysteine, n-acetyl-ι-cyteine, glutathione, thiourea, 2-mercaptoethanol and dithiotreithol and organic acids such as magic acid, citric acid, glycolic acid, taurine and kojic acid on polyphenol oxidate (PPO) activity were studied in order to establish if it reacts with oxidized product and/or directly inhibits the enzyme. To investigate the mechanism, the quantification of t-butylcatechol and 4-methylcatechol (phenolic compounds) as substates, their oxidized product and sulphydryl colorless additional compounds were determined by high performance liquid chromatograph (HPLC) method. Chromatographic results indicate that ascorbic acid, organic acids and lower level of cysteine reduced oxidized product of substrates back to their respective positions uf ο-diphenols. On the other hand, other thiols and high level of cysteine reacted with oxidative product of ο-diphenols and then produced sulphydryl colorless compounds. Cysteine apperars to have two types of mechanism of actions in the formation of oxidative products of substrates depending on its concentration; ascorbic acid-type and other thiols-types. The effect of ascorbic acid with thiols on polyphenol oxidase was determined by same method. Chromatographic results indicate that ascorbic acid was more reactive with oxidized product of substrates than thiols.

• The Korean Journal of Food And Nutrition
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• v.33 no.4
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• pp.419-427
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• 2020

The purpose of this study was to investigate the qualitative changes of the citron by identifying the type of solution and addition of the solution to prevent the browning reaction of the citron in a way that inhibits the browning of the citron. The browning inhibitor solution was investigated using the individual and mixture, and the results of the degree of browning and chromaticity showed that vitamin C+NaCl+cyclodextrin (CD) had the lowest browning of 0.52. In chromaticity, the ΔE values indicate that the higher the value, the greater the change in color, and the lowest value of the vitamin C+NaCl+CD mixture was 47.0, indicating that there was minimal browning compared to other treatment. The active change of the polyphenol oxidase (PPO) in the citron increased enzyme activity as the browning progressed, and the vitamin C+NaCl+CD solution was the lowest at 68.40 μ/g among the anti-browning solution. Based on these research results, it seems that the CD mixing solution can be used as a citron browning inhibitor.

• The Korean Journal of Food And Nutrition
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• v.30 no.5
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• pp.853-859
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• 2017

This study was conducted in an effort to investigate the effect of Maillard reaction products (MRPs) on enzymatic browning of burdock and their anti-oxidant activity. The MRPs were prepared by heating glucose and amino acids at $90^{\circ}C$, which served to produce a strong inhibitory effect on burdock polyphenol oxidase. As the reaction time of the solution containing glucose and amino acid increased at $90^{\circ}C$, the production of MRPs increased and intensity of the brown color deepened. When MRPs were prepared by heating at $90^{\circ}C$ for five hours, the absorbance of MRPs from glucose and lysine was 6.44, while those of glucose and glycine was 1.95. The MRPs synthesized from the glucose and lysine also reduced the pH of MRPs from 5.60 to 4.51, but those from glucose and glycine decreased slightly from 5.57 to 5.33. The Michealis-Menten constant value ($K_m$) of burdock PPO with pyrocatechol as a substrate was 16.0 mM, and MRPs were a non-competitive inhibitor against burdock PPO. The anti-oxidant activity of MRPs was measured by evaluating its radical scavenging activities of DPPH radicals, ABTS radicals and reducing power. The color intensity of MRPs produced by lysine and glucose were deeper than that produced by glucose and glycine. It was also found that MRPs produced from glucose and lysine exhibited stronger anti-oxidant properties than those produced by glucose and glycine.

• Journal of the Korean Society of Food Science and Nutrition
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• v.39 no.7
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• pp.1018-1023
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• 2010

This study was conducted to investigate quality changes of apple slab after pretreating with supercritical $CO_2$. L, a, b and color difference values were little changed at increasing temperature and pressure. Polyphenol oxidase was inhibited according to increment of supercritical $CO_2$ temperature and pressure. Springiness and hardness were increased at increasing pressure and temperature condition of pretreatment but hardness showed lower value than untreatment. The texture like sponge of dried apple slab was probably due to channels which were made during penetration and release of carbon dioxide.

• Food Science and Biotechnology
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• v.18 no.6
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• pp.1417-1422
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• 2009

This study was conducted to investigate the effect of ultrasound with ascorbic acid on the quality of fresh-cut apples. Prepared apple cubes were dipped in distilled water (US) or in 1% ascorbic acid solution (AS), both were treated with ultrasound at 40 kHz, while the other sample was just dipped in 1% ascorbic acid solution for 1 min (AA). All samples were stored at $4^{\circ}C$ for 12 days. AS treatment had an effect on apple cube color as indicated by its significantly higher L values and lower ${\Delta}E$ value whereas AA- and US-treated samples showed a considerable browning. Higher inhibition rate on browning and polyphenol oxidase (PPO) activity of 46 and 98%, respectively, were observed after AS treatment. The highest total phenolic content of AS-treated samples was shown during whole storage periods. This investigation revealed that the use of ultrasound in combination with ascorbic acid had a positive effect on quality maintaining of fresh-cut apples.

• Korean journal of food and cookery science
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• v.12 no.4
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• pp.535-540
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• 1996

Potato slices were dipped in solution of 2% CaCl$_2$, and 1% chitosan or preheated in each of these solutions for refrigeration for 4 weeks at 5$^{\circ}C$. Changes in L value, content of total phenol and chlorogenic acid and po lyphenol oxidase activity were determined. During refrigeration, it was found that L values of potato slices treated with CaCl$_2$, (CaPS) and those treated with chitosan (ChPS) increased. Contents of total phenol and chlorogenic acid of potato slices decreased, While potato slices preheated in CaCl, solution (Hcaps) showed much decreases. And polyphenol oxidase (PPO) activity of potato slices decreased except CaPS and decreases in PPO activities were much larger in preheated potato slices. From these results, of those treatments used, chitosan treatment combined with preheating have shown to be effective to control enzymatic browning of potato slices during refrigeration.

• Journal of the Korean Society of Food Science and Nutrition
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• v.15 no.2
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• pp.158-164
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• 1986

Polyphenol oxidase in apple (Golden Delicious) was extracted, partially purified and its properties were found as follows; Polyphenol oxidase showed optimum pH for activity at 6.5 and optimum temperature at $30^{\circ}C$ and high affinity to o-diphenol compounds. Cysteine, ascorbic acid and sodium metabisulfite appeared to be most effective inhibitors. EDTA showed a slight inhibition. During the enzyme was kept in test tube at $4^{\circ}C\;and\;20^{\circ}C$ for a week, polyphenol oxidase activity decreased sharply during the first four days at $20^{\circ}C$, then decreased slowly as the storage was prolonged. At $4^{\circ}C$, the polyphenol oxidase activity appeared to be relatively stable during the first two days before activity began to decline sharply. Polyacrylamide disc gel electrophoresis indicated four bands with polyphenol oxidase activity. Three bands and one band of the active bands were observed after heating for 1hr at $60^{\circ}C\;and\;70^{\circ}C$ respectively. The enzyme activity was observed 40% after treatment at $60^{\circ}C$ and 5% after treatment at $70^{\circ}C$. Therefore, no difference in the thermal stability was observed between active bands and the enzyme activity.