Microbial diversity in jiuqu and its fermentation features: saccharification, alcohol fermentation and flavors generation.

Chinese Baijiu, the national liquor of China, is also one of the world-renowned distilled spirits. Jiuqu, a fermentation starter, is the masterpiece of traditional food biotechnology with a long history in China. Compared to western brewing technology of using malt and yeast in stages, the mode of using jiuqu (or combined with pit mud, a activated sludge) for Baijiu brewing is recognized in China. So far, culture-dependent, molecular biology technology and omics approaches have provided deeper insights into study the jiuqu microbiome. Jiuqu is considered to be a microecosystem with diverse and unique microorganisms, in which fascinating features of saccharification, alcohol fermentation, and flavors generation appear. However, knowledge about microbial diversity of jiuqu and their roles involved in Baijiu fermentation is still fragmentary and not systematic enough. Therefore, this review introduced and compared three basic types of jiuqu starter: daqu, xiaoqu and fuqu. We described in detail the microbial succession during preparation of jiuqu, aiming to emphasize that succession process promotes to formation of its stable distribution of microbial community. We also summarized the main species originated from jiuqu and their various properties. Furthermore, reported results about fermentation features of saccharification, alcohol fermentation, and flavors generation in jiuqu microbiome were generalized, and these features were emphasized to play the potential role in Baijiu brewing. Although the current work is limited, promising clues can be traced for future investigation on comprehensive metabolic processes in jiuqu. KEY POINTS: • The various microorganisms present in jiuqu, and each has its specific property. • Microbial succession in preparation promotes to distribution of microbial community. • Jiuqu contributes the potential of saccharification, fermentation and flavors generation to Baijiu brewing.