摘要
苹果中的多酚氧化酶是引起苹果及苹果酒褐变的重要原因之一 ,用乳化剂及酚结合剂从苹果中提取多酚氧化酶 (PPO) ,研究其酶学性质 :不同底物的Km、Vm,反应的最适温度、pH及两种底物同时存在时的酶学效应 .结果表明 :4 甲基儿茶酚为最适底物 ,其最适温度 30℃ ,最适 pH4 .5 ,不同浓度咖啡酸对酶的影响不同 ,儿茶素对不同浓度绿原酸的酶促反应影响也不同 .研究几种效应物对酶活力的影响表明 :偏重亚硫酸钠、半胱氨酸、抗坏血酸为强烈抑制剂 ,羧酸类对酶具有抑制效应 。
Polyphenoloxidase is one of the major factors to cause the browning of apple and ciders. The characteristics of the polyphenoloxidase extracted from the apple fruit by sodium phosphate buffer ( 0.2 mol/L , pH 6.5)plus the sutable Triton X100 and PVPP were studied by using spectrophotometry. The best reaction condition is pH 4.5,30 ℃ and using 4 methylcatechol as the substrate. The enzymatic reaction is affected by the two phenolic compound mixture: Caffic acid affected the PPO activity, and catechin concentration also affected. The enzymatic reaction of the chlorogenic acid. Effect of several substrates on the activity of PPO was studied,and the result showed that L cysteine , ascorbic acid, and potassium pyrosulfite are the strong inhibitors. Carboxylic acid has the inhibitory effects, and cinnamic acid series has a stronger inhibiting effect than the benzonic acid series having the same structures.
基金
国家科技部"十五"重点项目 (2 0 0 1BA5 0 1A0F)
