Effects of papain, Lactiplantibacillus plantarum 1-24-LJ and their combinations on bacterial community changes and flavour improvement in Suanzhayu, a Chinese traditional fish

Suanzhayu is a traditional Chinese fermented fish that often faces a long fermentation time (about 1 month) and unstable quality. This study evaluated the combined effects of papain and Lactiplantibacillus plantarum 1-24-LJ, a selected starter culture, on the quality of Suanzhayu. The addition of L. plantarum and/or papain increased the content of alcohols, esters, ketones and umami amino acids (UAAs), but decreased the content of bitter amino acids (BAAs). Besides, Lactobacillus might play a role in reducing harmful bacteria and BAAs content and increasing UAAs content, while Lactococcus and Weissella contributed to the characteristic flavour of Suanzhayu. Overall, no significant improvement in sensory quality was observed with the addition of papain alone, while better quality and faster fermentation processes were obtained with the addition of L. plantarum 1-24-LJ alone or in combination with papain. The results contribute to quality control in Suanzhayu production and the selection of starter cultures.