花色苷的酶降解

Enzymatic Degradation of Anthocyanins

摘要:

综述了降解花色苷的酶类及其降解机理的研究进展。降解花色苷的酶有花色苷酶、多酚氧化酶、过氧化物酶和果胶酶。花色苷酶和果胶酶均能水解花色苷糖苷键产生花色素和糖,花色素很不稳定,因吡喃烊环极易开环可自发转换成无色衍生物。花色苷不能直接作为PPO或POD的底物;PPO和POD氧化、降解花色苷须依赖具邻二酚结构的其他酚类的存在,经连续型的偶联氧化机制实现,PPO和POD分别在氧和H₂O₂存在时将其他酚类氧化为邻位醌类,邻位醌将花色苷氧化为花色苷邻位醌、自身被还原为酚,邻位醌与花色苷醌间或花色苷醌相互间发生非酶促自发聚合、形成黑色素。花色苷的体内降解可能是若干种酶的同时催化下完成的,这为花色苷体内降解机理的研究和人工调控酶活性以稳定或降解花色苷提供参考。

Abstract:

The research advances in the enzymes degrading anthocyanins and their degradation mechanisms were summarized. The enzymes degrading anthocyanins include anthocyanase, polyphenol oxidase (PPO), peroxidase (POD) and pectinases. Anthocyanase and pectinase both hydrolyze the glucosidic bond of anthocyanins to produce anthocyanidins and saccharides, anthocyanidins are highly unstable and spontaneously change into colorless derivatives duo to the easy openning of their pyrylium rings. Anthocyanins can not directly act as PPO or POD substrates. The oxidation and degradation of anthocyanins catalyzed by PPO and POD must rely on the presence of other phenolics holding o-diphenol structure, and are realized by a coupled oxidation mechanism of consecutive-type. In the presence of O₂ and H₂O₂, respectively, PPO and POD oxidize other phenolics to o-quinones which oxidize anthocyanins to anthocyanin o-quinones and are reduced back to the native phenolics. Non-enzymatic self-associations happen between the o-quinones and the anthocyanin o-quinones or among the anthocyanin o-quinones, forming melanins. Therefore, the anthocyanins degradation in vivo may be realized by the simultaneous catalyzing of several enzymes, which could provide a reference for the exploration of the in vivo degradation mechanisms of anthocyanins and the artificial regulations of the enzyme activities to stabilize or degrade the anthocyanins.