传统农家酱产蛋白酶菌株的分离及其在豆浆的应用

豆浆富含植物蛋白，但由于植物蛋白相较动物蛋白不易被人体吸收。利用产蛋白酶菌株发酵豆浆，可将植物蛋白降解成多肽和氨基酸，提高其消化吸收率。传统农家酱是以大豆为主要原料的传统发酵食品，含有大量能够水解大豆蛋白的优良菌株。该研究从传统农家酱中分离到8株产蛋白酶的芽孢杆菌并用于豆浆处理，处理后豆浆的可溶性肽含量显著提高，其中菌株BJ-20处理效果最显著；氨基态氮含量和水解度也有显著变化，其中BJ-6处理后的豆浆最佳，氨基态氮含量提高了10.87%，水解度为23.49%。同时，处理后豆浆的组织状态得到了明显改善。本研究丰富了豆类发酵菌种库，提高了大豆蛋白利用率，丰富了大豆产品种类，为大豆保健产品开发提供参考及理论支持。

Isolation of protease strains from traditional soybean paste and their application in soymilk

Fermentation is one of the most common-used technologies in food processing. The nutritional value of food can also be maximized to increase the flavor of food. Among them, soymilk is rich in plant protein among food products. But the plant protein is relatively difficult to be absorbed by the human body. Protease-producing strains can be used to treat soy milk. Specifically, the plant protein can be converted into peptides and amino acids for better digestion and absorption rate. The protease-active strains can be screened from the traditional soybean fermented foods, and then serve as the nutrient source for the growth and reproduction of the soybeans. The proteases can be produced more suitable for the soy protein. The unique production process can also be found in the traditional soybean pastes in Northeast China. Specifically, the steamed soybeans are generally fermented to prepare using multiple procedures, such as stir-frying, brick-making, fermentation, and sauce. A long production history can then produce the unique flavor of typical fermented foods. Since manual production is often brewed in individual workshops, the types of fermentation microorganisms vary greatly, depending mainly on the brewing environment. Furthermore, the current fermentation is focused mostly on the Pixian bean paste. Many functional strains have been found in the Pixian bean paste, including the protease-producing strains. And these strains have been applied to functional foods, such as the descending amines and the inhibiting growth of Aspergillus flavus. Taking the Fushun farmhouse soybean paste as the research object, a series of experiments were carried out to screen the protease strains through the hydrolysis circle. Morphological observation was then characterized to identify eight strains with better decomposition of soybean protein. 16S rDNA sequencing as Bacillus included the 1 strain of Bacillus zhangzhouensis, 1 strain of Bacillus velezensis, 2 strains of Bacillus subtilis, 1 strain of Bacillus siamensis, 2 strain of Bacillus methylotrophicus, and 1 strain of Bacillus tequilensis. The screened strains were used for the soy milk fermentation after the safety analysis. The systematic evaluation was performed on the soluble peptide content, amino nitrogen content, hydrolysis degree, and sensory of soymilk before and after fermentation. The results showed that the soluble peptide content of soy milk increased significantly during production. There was the most significant effect of soy milk after treatment with BJ-20, with an increase of 37.23%. In addition, the amino nitrogen and hydrolysis degree of soymilk also changed significantly. Among them, the effect of soymilk treated with BJ-6 was the most significant, with the amino nitrogen increasing by 10.87% and the hydrolysis degree being 23.49%. The sensory evaluation showed that the tissue state of soy milk was significantly improved after treatment. The finding can enrich the bean processing in the diversity of soybean products. A strong reference and theoretical support can also be provided for the soybean health function.