Abstract
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.
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