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Polyphenol oxidase (PPO) was found to be the main cause of Guankou wine browning by investigating the browning index (BI) and the phenolic substances during the winemaking process. PPO was purified via temperature‐induced phase partitioning, ammonium sulfate precipitation, and chromatography. The estimated molecular weights obtained by SDS‐PAGE were 38 and 45 kDa. PPO was found to have an optimum pH and temperature of 4.6 and 30°C, respectively. The minimum time required to achieve inactivation was 10 min at 75°C. PPO from Guankou grape showed the highest binding affinity with caffeic acid, and a higher affinity for catechin than that from other grape varieties. The addition of ascorbic acid effectively reduced the browning of Guankou wine. Practical applications: Guankou grape is the main variety in Jianshi County, Hubei Province, China. The enzymatic browning process of Guankou grapes and PPO characterization after purification were investigated, and it was found that the unique PPO was responsible for the rapid browning of Guankou wine. A suitable inhibitor was also found to prevent that from happening. These results provide a more comprehensive understanding of the features of Guankou grape PPO, and may assist with the effective control of browning occurring during wine making. [ABSTRACT FROM AUTHOR]

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Acetes chinensis (belonging to the Decapoda Sergestidae genus) is widely distributed in East Asian waters and is extremely widespread and present in the shallow coastal areas of China. Polyphenol oxidase (PPO), which was extracted from Acetes chinensis, was purified in a four-step procedure involving phosphate-buffered saline treatment, ammonium sulphate precipitation, DEAE-Cellulose chromatography, and Phenyl-Sepharose HP chromatography, and then, its biochemical characterization was measured. The specific activity of the purified enzyme was increased to 643.4 U/mg, which is a 30.35 times increase in purification, and the recovery rate was 17.9%. L-dopa was used as the substrate, the enzymatic reactions catalyzed by PPO conformed to the Michaelis equation, the maximum reaction velocity was 769.23 U/mL, and the Michaelis constant Km was 0.846 mmol/L. The optimal pH of PPO from Acetes chinensis was 7.5, and the optimal temperature was 35 °C. The metal ions experiment showed that Mn2+ and K+ could enhance the activity of PPO; that Ba2+ and Ca2+ could inhibit the activity of PPO; and that Cu2+ had a double effect on PPO, increasing the PPO activity at low concentrations and inhibiting the PPO activity at high concentrations. The inhibitor experiment showed that the inhibitory effects of EDTA and kojic acid were weak and that ascorbic acid and sodium pyrophosphate had good inhibitory effects. The purification and characterization of Acetes chinensis serve as guidelines for the prediction of enzyme behavior, leading to effective prevention of enzymatic browning during processing. [ABSTRACT FROM AUTHOR]