fungal community succession and flavor function in fire cycle during the production of medium-high temperature Daqu

Abstract:

[Background] Daqu fungi provide starter and saccharifying agents for Baijiu fermentation process and fire cycle provides important flavor substances for Baijiu production, while the fungal community succession and flavor function in fire cycle remain unclear. [Objective] To explore the succession and flavor function of the fungal community in the fire cycle of medium-high temperature Daqu, and provide a theoretical support for optimizing the making process of Daqu and improving the quality of Baijiu. [Methods] The headspace solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was employed to detect the flavor compounds, and internal transcribed spacer (ITS) amplicon sequencing was performed to analyze the fungal community structure. With the physical and chemical parameters of Daqu fire cycle, the redundancy analysis was conducted to explore fungal succession and flavor function of fire cycle during the production of Daqu. [Results] Some ester compounds (ethyl acetate, ethyl butyrate, ethyl hexanoate, methyl-alpha-galactopyranoside, and ethyl oleate), aromatic compounds (ethyl phenylacetate, 2,4-dimethylbenzaldehyde, benzyl alcohol, and phenethyl alcohol), acid compounds (acetic acid), alcohol compounds (3-octanol and furfuryl alcohol) had higher content in the fire cycle than in the surface and core of medium-high temperature Daqu. From the fourth stage, the fire cycle had the temperature higher than 40℃ and the reducing sugar content greater than 2%, and the Maillard reaction occurred to form the fire cycle. Pichia kudriavzevii and Saccharomycopsis fibuligera were the dominant fungi in the fire cycle, with the relative abundance over 95% at the 2-3 stage of Daqu production. At this time, the fungal diversity in the fire cycle was the lowest. [Conclusion] The succession of fungal community in the fire cycle of medium-high temperature Daqu was mainly affected by reducing sugar content and temperature. The fire cycle provided important ester compounds, aromatic compounds, acid compounds, alcohol compounds and other flavor substances for Baijiu production, and supplied the core yeast species for Baijiu fermentation, such as P. kudriavzevii and S. fibuligera. Fire cycle played an important role in the production of Baijiu. Our study further deepened the understanding of the fire cycle, and offered a theoretical basis for the adjustment of Daqu-making process and the improvement of Baijiu quality.