Environmental factors drive microbial succession and huangjiu flavor formation during raw wheat qu fermentation

As the core raw material of huangjiu (Chinese rice wine) production and brewing, changes of physichemical factors during the fermentation process significantly affect the succession of the microbial community of raw wheat qu (RWQ), also playing important role in huangjiu quality. In this report we analyzed the community structure and driving force RWQ microorganisms with different processes (manual qu, MAQ; mechanical qu, MEQ), and evaluating the flavor of huangjiu. The production procedure was divided into three stages. Dominant microorganisms were Aspergillus, Alternaria, Epicoccus, Bacillus, Pantoea, Saccharopolyspora and Staphylococcus. In early stage, microbial community of MAQ was significantly correlated with temperature and water content, oxygen in middle stage, while no significant driving force in the last stage. Water content and oxygen affected MEQ community significantly in early stage, while in the final stage, fungal community was affected by both temperature and water content, and bacterial community was significantly correlated with oxygen. Glucoamylase activity reached its maximum at 50 °C, while the α-amylase activity decreased with the rise of temperature. The highest amylase activity was obtained with 19% initial water addition. Amylase activity showed positive correlation with the thickness of RWQ. The total amount of organic acids was higher in mechanical huangjiu at the end of pre-fermentation. Contents of n-hexanol, ethyl isovalerate, ethyl hexanoate and guaiacol in manual huangjiu were significantly higher than those in mechanical one, while the content of 4-vinylguaiacol was lower.