Endo-β-1, 4-xylanase (EC 3.2.1.8) is a key enzyme in the degradation of Arabinoxylan (AX). AX and its degradation products are the key substances that affect the viscosity, turbidity, filtration speed, alcohol, foam performance, and health care function of wheat beer. A wheat malt-derived endo-β-1, 4-xylanase was isolated and purified by our group in the previous stage. The aim of this study was to investigate the effects of the wheat malt-derived endo-β-1, 4-xylanase addition on the quality and composition of AX in hopped wort and wheat beer. The results showed that the content and the average degree of polymerization (avDP) of water-soluble arabinoxylan (WEAX) in hopped wort and wheat beer decreased with the increase of the addition level of the wheat malt-derived endo-β-1,4-xylanase. When the addition of wheat malt-derived endo-β-1,4-xylanase was 2.5 times of the activity of endo-β-1,4-xylanase in raw malt, the degradation rate of WEAX in hopped wort was the maximum (33.71%), and the avDP of WEAX was the minimum (29.74) at the addition level of the endo-β-1,4-xylanase was 2 times. The viscosity and turbidity of hopped wort and wheat beer decreased continuously with the increase of the addition level of the endo-β-1,4-xylanase, while the foam stability of wheat beer increased continuously. Wheat malt-derived endo-β-1,4-xylanase could decrease the content of 1320-6200 Da polysaccharide in wheat beer, but increase the content of<1320 Da polysaccharide.
This study investigated the hydrolysis effect of the endopeptidase from wheat malt on the soybean meal proteins. The results indicated that the endopeptidase broke the peptide bonds of soybean meal proteins and converted the alcohol- and alkali-soluble proteins into water-soluble and salt-soluble proteins. In addition, wheat malt endopeptidase did not break the disulfide bonds between proteins but affected the conformation of disulfide bonds between substrate protein molecules, which were changed from the gauche-gauche-trans (g-g-t) vibrational mode to the trans-gauche-trans (t-g-t) vibrational mode. Wheat malt endopeptidase exhibited the highest enzymatic activity at 2 h of enzymatic digestion, demonstrating the fastest hydrolytic rate of soybean meal proteins. Compared with the samples before enzymatic hydrolysis, the total alcohol- and alkali-soluble proteins were decreased by 11.89% but the water- and salt-soluble proteins were increased by 11.99%, indicating the hydrolytic effect of endopeptidase. The corresponding water-soluble proteins had molecular weights of 66.4–97.2, 29–44.3, and 20.1 kDa, while the salt-soluble proteins had molecular weights of 44.3–66.4, 29–44.3, and 20.1 kDa, respectively. The degree of enzymatic hydrolysis of soybean meal reached the maximum at 8 h. The newly created proteins exhibited significantly antioxidant properties, which were inversely related to the molecular weight. Proteins with molecular weight <3 kDa had the highest antioxidant performance with an antioxidant capacity of 1.72 ± 0.03 mM, hydroxyl radical scavenging rate of 98.04%, and ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] radical scavenging capacity of 0.44 ± 0.04 mM.
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