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

Summary 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.