Abstract Beer subjected to forced aging by five (Medium) or ten (High) heat/chill cycles (60 °C 48 h/0 °C 24 h) showed increased turbidity from 5.4 ± 0.4 EBC units without forced aging to 12.9 ± 0.7 and 48 ± 2 EBC units for Medium and High forced aged beers, respectively. The particle size diameter increased from 100–200 nm to 10–30 µm. The colloidal changes were associated with modifications of the low molecular weight fraction (∼1 kDa), which were found to increase in the soluble part of the beer as identified by size exclusion chromatography. Polyphenol analyses by liquid chromatography and mass spectrometry showed significant losses of gallic acid, hydroxyphenyllactic acid, salicylic acid, chlorogenic acid, vanillic acid, epicatechin, pyrocatechuic acid, ferulic acid, and luteolin during the forced aging, indicating that these phenolic compounds took part in the colloidal changes, proposedly upon polymerization into tannins. Gel electrophoresis coupled with staining by nitroblue tetrazolium indicated polyphenol modification of all proteins and especially LTP1 (lipid transfer protein 1). It is proposed that the di- and tri-hydroxyl phenolic compounds upon oxidation to quinones react with protein nucleophiles of especially LTP1 to generate the initial covalent bonds, which eventually leads to larger insoluble permanent haze particles.

中文翻译：

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共价蛋白质-多酚键合是啤酒中雾霾形成的初始步骤

摘要 经过五次（中）或十次（高）热/冷循环（60°C 48 小时/0°C 24 小时）强制老化的啤酒显示浊度从 5.4 ± 0.4 EBC 单位没有强制老化增加到 12.9 ± 0.7 和48 ± 2 EBC 单位分别用于中度和高度强制陈酿啤酒。粒径从 100-200 nm 增加到 10-30 µm。胶体变化与低分子量部分 (~1 kDa) 的改变有关，通过尺寸排阻色谱法发现，啤酒的可溶部分增加了。液相色谱和质谱的多酚分析表明，在强制老化过程中，没食子酸、羟苯基乳酸、水杨酸、绿原酸、香草酸、表儿茶素、焦儿茶酸、阿魏酸和木犀草素有显着损失，表明这些酚类化合物参与了胶体变化，建议在聚合成单宁时。凝胶电泳结合硝基蓝四唑染色表明所有蛋白质都发生了多酚修饰，尤其是 LTP1（脂质转移蛋白 1）。提出二羟基和三羟基酚类化合物在氧化成醌后与蛋白质亲核试剂特别是 LTP1 反应生成初始共价键，最终导致更大的不溶性永久性雾霾颗粒。