Study On Effects Of Additional Amounts Of Mature Daqu On Microbial Community Dynamics And Flavor Compounds During High-temperature Daqu Fermentation

High-temperature daqu(HT-daqu),also known as sauce-flavor daqu,is mainly made from wheat by artificial accumulation and natural fermentation.It is regarded as an important saccharifying,fermenting and flavor-generating agent in sauce-flavor baijiu fermentation.In production of HT-daqu,people often use a certain amount of mature HT-daqu as culture starter,and this special process is considered to have the advantages of improving product quality,and improving the stability of quality between batches.So far,no studies have been conducted to evaluate the effects of additional amounts of mature daqu on HT-daqu fermentation.In this research,groups with different additional amounts of mature daqu were designed for mass-produced HT-daqu.The dynamics of flavor composition and microbial community structure in different groups were analyzed using flavor-chemistry and micro-environmental technology.The main conclusions are as follows.(1)Samples with additional mature daqu reached higher habitat temperature more quickly during fermentation,but the excessive acidification of daqu habitat could be caused by the high addition of mature daqu to some extent.A total of 79 kinds of volatile flavor compounds were detected in all collected samples,including 18 kinds of alcohols,15 kinds of esters,22 kinds of aldehydes and ketones,and 24 kinds of other compounds.Among them,alcohols and esters were the major categories.Various flavor substances mainly accumulated in the rapid-heating period,and as time progresses,the contents of these compounds showed an overall trend of increasing at first and then decreasing.(2)Compared with samples in the control group,samples in the experimental group with additional mature daqu showed a higher degree of dynamic change in bacterial community structure.Weissella,Lactobacillus,Staphylococcus,Pantoea,Pediococcus,etc.were the dominant bacterial taxa in the early fermentation stage,and their growth and metabolic activities created a rather acidic environment for daqu fermentation as a whole.Bacillus,Kroppenstedtia,Thermoactinomyces,Oceanobacillus,Virgribacillus,etc.can tolerate high temperature and become dominant in the late stage.The special bacterial species that transferred from mature daqu were Thermoactinomyces vulgaris,Weissella hellenica,and Kroppenstedtia eburnean.(3)Compared with samples in the control group,samples in the experimental group with additional mature daqu showed a lower degree of dynamic change in fungal community structure.Wickerhamomyces,unidentified Saccharomycetales,Aspergillus,and pathogenic fungi of Gramineae plants mainly existed at the beginning of fermentation,and then were gradually eliminated.Thermomyces,Thermoascus,and Byssochlamys were the symbolic fungal taxa in the fermented samples collected on the days 7,14,and 30,respectively,and these genera were considered to have important influence and significance on the respective microbial communities.The special fungal species that transferred from mature daqu were Thermoascus crustaceus,Thermomyces lanuginosus,and Saccharomycopsis fibuligera.(4)Based on the relative abundance matrices of the microorganisms and volatile flavor compounds,we presented Spearman's correlation analysis via heatmaps.Bacillus,Kroppenstedtia,Oceanobacillus,Virgribacillus,etc.had significant positive correlations with pyrazines and aromatics.Lactobacillus,Pediococcus,and Klebsiella had significant positive correlations with 2-methyl-1-propanol.Rhizomucor,Trichosporon,Meyerozyma,Wickerhamomyces,and Candida were positively correlated with some alcohols,esters,and aldehydes,but negatively correlated with pyrazines.