Li Xiaomin, Jin Zhao, Gao Fei, Lu Jian, Cai Guolin, Dong Jianjun, Yu Junhong, Yang Mei
The Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University , 1800 Lihu Road, Wuxi 214122, People's Republic of China.
J Agric Food Chem. 2014 Jun 18;62(24):5643-50. doi: 10.1021/jf405699z. Epub 2014 Jun 10.
Barley protein Z7 (BSZ7) is a well-known serine protease inhibitor that was regarded as a major effector of beer foam stability. Moreover, it has also been suggested to participate in haze formation and affect wort filterability. The present study purified BSZ7 from barley malt and characterized its secondary structure and modification, as well as its relationship with peroxidase, to elucidate the molecular base of BSZ7 that supports its multiple roles in malt and beer. It was found that after 30 min of heating, the secondary structure was not affected. BSZ7 has no inhibiting effect on nonspecific protease originated from malt, suggesting its negative role in wort filterability was accomplished by other means. Furthermore, the glycation of BSZ7 by the Maillard reaction may make some contribution to its survival during wort boiling. The interaction of BSZ7 with polysaccharides and polyphenols found by adding experiment may explain how it acts as a negative factor on wort filterability. Greater understanding of BSZ7 and other proteins of malts will lead to better improvements in brewing quality.
大麦蛋白Z7（BSZ7）是一种著名的丝氨酸蛋白酶抑制剂，被认为是啤酒泡沫稳定性的主要影响因素。此外，也有人认为它参与了啤酒浑浊的形成并影响麦芽汁的过滤性。本研究从大麦麦芽中纯化了BSZ7，并对其二级结构、修饰以及与过氧化物酶的关系进行了表征，以阐明支持其在麦芽和啤酒中发挥多种作用的分子基础。研究发现，加热30分钟后，二级结构未受影响。BSZ7对麦芽中的非特异性蛋白酶没有抑制作用，这表明其在麦芽汁过滤性方面的负面作用是通过其他方式实现的。此外，美拉德反应导致的BSZ7糖基化可能对其在麦芽汁煮沸过程中的存活有一定贡献。通过添加实验发现的BSZ7与多糖和多酚的相互作用或许可以解释它如何成为麦芽汁过滤性的负面因素。对BSZ7和其他麦芽蛋白有更深入的了解将有助于更好地提高酿造品质。
