香草兰O-β-葡萄糖苷酶底物特异性和温度稳定性研究

Characterization of O-β-glucosidase Activity in Vanilla planifolia and the change during the Curing Crocess of Vanilla Beans

香草兰是最重要的食品香料之一,其主要香味成分为香兰素,主要存在于香草兰豆荚中。香兰素一般由成熟豆荚中的香兰素葡萄糖苷经过漫长的发酵过程转化而来。O-β-葡萄糖苷酶在发酵生香的过程中起着关键作用。研究结果表明:香草兰的根、茎、叶和豆荚中都具有O-β-糖苷酶活性,豆荚活性最高,叶片活性最低;来自不同器官的O-β-糖苷酶的底物特异性一致,都能降解香兰素糖苷、2-NPG、4-NPG,都不能降解n-OG及硫代葡萄糖苷;香草兰糖苷酶提取物在50～60℃处理1 min,对酶活性影响很小,70℃处理1 min,酶活性丧失约40%,说明香草兰糖苷酶对高温具有一定耐受性,杀青后剩余糖苷酶活性在漫长的发酵过程中能够满足酶促反应的需求。

Vanilla is one of the most important food spices.Its main aromatic component is vanillin,presented mostly in the pods as a form of vanillin glucoside.The aroma is developed by months-long curing process in which the glucovanillin becomes degraded by glucosidases,as well as other related reactions.Thus glucosidases play a central role in the curing.We studied the enzymatic properties of the glucosidases in vanilla in this research.Results indicated that all the tested organs of vanilla presented O-β-glucosidase activity,while the bean has the highest activity,the stem and root had the moderate and the leaf had the lowest.The O-β-glucosidases from all the tissues had the same substrate spetrum,in which glucovanillin,2-NPG,4-NPG were digested,but O-β-glucoside,n-OG and O-β-thioglucosides were not degraded by vanilla O-β-glucosidases.Thermostability experiment indicated that the O-β-glucosidases were relatively stable to short term high temperature treatment.No obvious loss of activity was observed when the enzymes were treated at 50~60 ℃ for 1 min,and only 40% of activity was lost when the enzymes were treated at 70 ℃ for 1 min.These results indicated that the internal O-β-glucosidases were enough to the subsequent fermentation process after the killing.