Insights into whereby raw wheat Qu contributes to the flavor quality of Huangjiu during brewing

Abstract

The influence of raw wheat Qu (RWQ) on the flavor quality of Huangjiu was investigated in this study. When used as a single saccharification starter, RWQ showed poor fermentation performance during Huangjiu brewing. However, as a co-fermentation starter with cooked wheat Qu (CWQ), RWQ considerably enhanced flavor quality of the resultant Huangjiu by promoting the accumulation of fatty acid ethyl esters (FAEEs) with odor activity values exceeding 1. Based on dynamic changes in bacterial diversity during Huangjiu brewing, a three-stage fermentation mode was identified for the first time. During stage III (5–15 d), the relative proportions of predominant genera Weissella and Lactococcus, which were strongly associated with the synthesis of FAEEs, were significantly adjusted by the co-fermentation of RWQ with CWQ. Moreover, co-fermentation of RWQ with CWQ reduced the bacterial diversity of Huangjiu samples, and this was strongly related to the total acidity (R2 = 0.867) and ethanol (R2 = 0.802) content. Therefore, the proportions of predominant bacteria were changed by RWQ, which affected bacterial diversity and enhanced the flavor quality of Huangjiu. Controlling environmental factors during brewing is suggested as a feasible way to regulate the proportions of bacterial genera, thereby regulating the flavor characteristic in the resultant wine.