荔枝与荔枝酒褐变控制

以荔枝及荔枝酒为试料，研究荔枝多酚氧化酶(PPO)的酶学特性及荔枝酒发酵过程中的褐变机理及控制措施。结果表明：荔枝PPO存在同功酶，荔枝PPO最适底物为没食子酸；以没食子酸为底物，荔枝PPO最适反应pH值为8.0，最适反应温度50℃，荔枝PPO的动力学参数为：米氏参数(Km)为26.033mmol/L，最大反应速度(Vmax)为34.816g/(L·min)；荔枝PPO对酸碱、对热稳定性较差；荔枝酒发酵过程中褐变的主要原因是其PPO引起的酶促褐变。因此，低温贮藏和高温热处理可有效抑制荔枝及荔枝酒在贮藏和加工中酶促褐变反应。

Browning Control of Litchi and Litchi Wine

In the present study, litchi and litchi wine were used as the materials to study the properties of polyphenol oxidase (PPO) in litchi, and explore browning mechanisms and controlling strategies of litchi wine during fermentation process. The isoenzymes of PPO were observed in litchi and the optimal substrate of PPO in litchi was gallic acid. The optimal pH and temperature for PPO from litchi were 8.0 and 50 ℃ using gallic acid as the substrate. Kinetic parameters such as Km and Vmax of PPO from litchi were 26.033 mmol/L and 34.816 g/(L·min), respectively. The PPO from litchi was not stable at the conditions of 50－80 ℃, strong acid and strong alkali. Higher PPO activity in litchi was the major browning cause of litchi wine during fermentation process. Therefore, low-temperature storage and heating treatment can effectively inhibit the browning of litchi and litchi wine.