大麦、麦芽和啤酒酿造中的内源性氧化还原酶

由于大麦和麦芽中存在的内潭性氧化还原酶的作用，使内源性多酚、不饱和脂类等物质被氧化，导致成品啤酒风味稳定性和非生物稳定性的降低。酶促氧化反应可发生在不同的酿造阶段，包括发芽、焙爆和糖化等环节。五种主要的内源性氧化还原酶中，超氧化物歧化酶是最为重要的抗氧化酶，可防止超氧阴离子自由基的危害；而过氧化氢酶可催化具有活性的H2O2生成如，由此构成了清除活性氧的初级抗氧化酶体系。过氧化物酶和多酚氧化酶分别在H2O2和O2存在的情况下，可催化内源性酚类底物生成具有活性的醌类物质，所产生的次级氧化产物可改变啤酒的品质。脂肪酸氧化酶可氧化不饱和脂肪酸生成可挥发性的醛类物质，是导致啤酒风味老化的关键酶。酶促氧化的结果在成品啤酒上主要表现为老化异昧的出现、形成混浊、苦味和收敛性的改变，以及色泽的加深等。本文综述了这五种酶的基本性质，在制麦和糖化过程中的变化及其影响，并探讨了对啤酒酿造的影响。

Endogenous Oxidoreductases in Barley, Malt and Brewing Processes

Endogeanus phenolic compounds and unsaturated lipids could be oxidated by endogenous oxidoreductasns survived in barley and malt.The actions of oxidoreductases could lead to beer flavour deteroration. Enzymatic-mediated oxidative reaction takes place duriog different stages of brewing processes, including barley germinatian, malt kilning, and mashing. Among the main oxidoreductases related to beer quality, superoxide dismutase is one of the most important antioxidative enzymes, which protects the medium from superoxide radicals. H2O2 could be catalyzed hy eatalase and gives rise to mofaculas oxygen, which constitute the primal, antioxidant enzyme system of scavenging reactive oxygen. The endogenous polyphenols could be catalyzed into reactive quinonic compounds by poroxidase and polyphenoloxidase under H2O2 and O2-mediated oxidation respoctively. Lipoxygenase, which catalyzes the oxidation of unsaturated fatty acids, is mostly responsible for the production of volatile aldehydes. The action of oxidereducrases could lead to flavour deterioration resulting in the developraent of staling and off-flavours, occurrence of haze,modification of bittemess, astringency and color of finished beer. In this review, the main characteristics and the development of those enzymes during malting and mashing were described. Their effects on brewing processes were also discussed.