中高温大曲制作过程中火圈真菌菌群演替规律及其风味功能

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

摘要:

[背景] 大曲真菌为白酒发酵过程提供发酵剂和糖化剂，火圈为白酒生产提供重要的风味物质，但针对火圈真菌的菌群演替规律及风味功能尚不清楚。[目的] 探索中高温大曲火圈真菌菌群演替规律及风味功能，为优化制曲工艺，提升白酒品质提供理论支撑。[方法] 使用顶空固相微萃取结合气相色谱质谱联用技术和内转录间隔区扩增子测序技术，结合中高温大曲制作过程火圈的理化参数，采用冗余分析的手段对大曲制作过程中火圈真菌演替规律及风味功能进行解析。[结果] 大曲火圈中的乙酸乙酯、丁酸乙酯、正己酸乙酯、乳酸吡喃糖苷甲酯和油酸乙酯等酯类化合物，苯乙酸乙酯、2，4-二甲基苯甲醛、苯甲醇和苯乙醇等芳香族化合物，酸类化合物乙酸，醇类化合物3-辛醇、糠醇等化合物的含量高于曲皮、曲心中的含量。大曲制作过程中从第4阶段开始，火圈位置温度>40℃，还原糖的含量>2%，产生美拉德反应，火圈逐渐形成。库德里阿兹威氏毕赤酵母（Pichia kudriavzevii）、扣囊复膜酵母（Saccharomycopsis fibuligera）是火圈中的优势真菌，在大曲制作的第2-3阶段占据了95%以上的丰度，此时火圈真菌的多样性最低。[结论] 中高温大曲火圈真菌群落演替主要受还原糖含量和温度的影响。大曲火圈为白酒生产提供了重要的酯类、芳香族、酸类、醇类化合物等风味物质，以及P.kudriavzevii、S.fibuligera等白酒发酵的核心酵母菌群，对白酒的生产起着重要的作用。研究结果进一步加深了对火圈的认识，为制曲工艺的调整、白酒品质的提升提供理论依据。

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.