Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
Department of Biomedical Sciences, University of Copenhagen , Blegdamsvej 3, DK-2200 Copenhagen N, Denmark.
J Agric Food Chem. 2017 Dec 13;65(49):10820-10828. doi: 10.1021/acs.jafc.7b05012. Epub 2017 Nov 29.
Thiol-containing proteins have been suggested to have antioxidative properties in beer. A kinetic model has been setup for the reactivity of thiols during early stages of oxidative degradation of beer. Kinetic analysis based on the proposed reaction mechanism allowed evaluation of the relative reactivity of beer components, such as bitter acids from hops and polyphenols. The rate constants for the reaction of 1-hydroxyethyl radicals, which are generated during radical mediated oxidation of ethanol in beer, with hop bitter acids and thiols were very similar, and the concentration of these compounds in beer is therefore essential for the relative reactivity. For a standard pilsner beer with 35 international bitter units with typical concentrations of thiols and hop bitter acids, thiols were found to react with ca. 9% of 1-hydroxyethyl radicals, while bitter acids from hops accounted for ca. 88% of the reaction with 1-hydroxyethyl radicals. Polyphenols were not found to account for any major part of the reaction with 1-hydroxyethyl radicals due to low reaction rates and low concentrations in pilsner beer compared to the other components. The kinetic model suggests that the concentration of thiols has to be increased in order to contribute with any significant antioxidative protection and that the fate of thiols during oxidation must be considered since some thiol oxidation products may induce further damage.
含巯基的蛋白质被认为具有啤酒中的抗氧化特性。建立了一个动力学模型，用于研究啤酒氧化降解早期阶段巯基的反应性。基于所提出的反应机制的动力学分析，可以评估啤酒成分的相对反应性，如啤酒花中的苦味酸和多酚。在啤酒中，自由基介导的乙醇氧化过程中生成的 1-羟乙基自由基与啤酒花苦味酸和巯基的反应速率常数非常相似，因此这些化合物在啤酒中的浓度对相对反应性至关重要。对于具有 35 个国际苦味单位的典型浓度的巯基和啤酒花苦味酸的标准皮尔森啤酒，发现巯基与约 9%的 1-羟乙基自由基反应，而啤酒花中的苦味酸则与约 88%的 1-羟乙基自由基反应。由于与其他成分相比，多酚的反应速率较低，浓度较低，因此在与 1-羟乙基自由基的反应中，多酚并没有占到很大的比例。该动力学模型表明，为了提供任何有意义的抗氧化保护，必须增加巯基的浓度，并且必须考虑巯基在氧化过程中的命运，因为一些巯基氧化产物可能会导致进一步的损伤。
