半胱氨酸控制鲜切苹果褐变的生理机制

为研究半胱氨酸对鲜切苹果褐变控制的生理机制，以鲜切苹果为研究对象，采用0.5 g/L的半胱氨酸溶液处 理1 min，分析贮藏过程中鲜切苹果褐变指数（browning index，BI）、多酚氧化酶（polyphenol oxidase，PPO）和 抗氧化酶活力、抗氧化物质和丙二醛（malondialdehyde，MDA）质量摩尔浓度及抗氧化能力的变化。结果表明， 与蒸馏水处理相比，半胱氨酸处理能够显著抑制鲜切苹果的褐变，在贮藏初期半胱氨酸处理降低了鲜切苹果的PPO 活力，同时在贮藏过程中不同程度提高了鲜切苹果的抗氧化酶活力以及抗氧化能力，减缓了抗氧化物质在贮藏过程 中的损失，并且抑制了MDA的积累。相关性分析显示，鲜切苹果的BI值与抗坏血酸含量、过氧化氢酶活力以及抗 氧化能力呈极显著负相关（P＜0.01），与MDA质量摩尔浓度呈极显著正相关（P＜0.01）。因此，半胱氨酸可能是 一方面通过抑制鲜切苹果的PPO活力，另一方面通过提高其抗氧化能力，延缓贮藏过程中的组织褐变。

Physiological Mechanism for Browning Inhibition in Fresh-Cut Apple by Cysteine

The purpose of this study was to explore the physiological mechanism for browning inhibition in fresh-cut apple by cysteine. Fresh-cut apples were dipped in 0.5 g/L cysteine solution for 1 min. The effect of cysteine treatment on browning index (BI), the activities of polyphenol oxidase (PPO) and antioxidant enzymes, the contents of antioxidant substances and malondialdehyde (MDA) and non-enzymatic antioxidant capacities was evaluated. The results showed that cysteine treatment significantly inhibited surface browning in fresh-cut apples during storage and resulted in lower PPO activity at the early stage of storage. Furthermore, cysteine treatment enhanced the activities of antioxidant enzymes, improved antioxidant capacity and the contents of antioxidant substances, and inhibited the accumulation of MDA at the same time. Statistical analysis indicated that BI was significantly negatively correlated with ascorbic acid content, catalase (CAT) activity, and antioxidant activity (P < 0.01), while there was a positive correlation between BI and MDA content (P < 0.01). Collectively, these finds suggest that cysteine treatment can inhibit PPO activity and enhance antioxidant capacity, thereby retarding the browning of fresh-cut apples during storage.