Comparison of fungal communities and flavour substances in surface and inner layers of fermented grains during stacking fermentation of sauce-flavour baijiu

Yeast community in the first-round fermentation of sauce-flavor Baijiu: Source, succession and metabolic function

Yeasts play a crucial role in determining the quality and yield of sauce-flavor Baijiu, yet the source, succession, and metabolic functions of the yeast community in fermented grains during stacking fermentation remains unclear. In this study, amplicon sequencing combined with solid-state fermentation was used to investigate the structure and function of yeast community during the first-round fermentation of sauce-flavor Baijiu. The richness and diversity of yeast community increased throughout fermentation, with 83.05 % of yeast ASV sourced from the fermentation environment. Fourteen yeast genera were identified, with Wickerhamomyces (29.6 %), Saccharomycopsis (25.0 %), and Torulaspora (14.9 %) being the predominant genera. These genera showed distinct spatial distributions throughout the fermentation stack. Spearman correlation analysis indicated positive correlations between the three genera and multiple volatiles in fermented grains alcohols and esters. After solid-state fermentation in pure culture, T. delbrueckii ME22, S. fibuligera ME8, and W. anomalus ME57 produced distinct floral, fruity, and sweet flavor compounds, such as phenylethyl alcohol, isoamyl alcohol, ethyl acetate, phenethyl acetate, and isoamyl acetate. T. delbrueckii ME22 demonstrated a great capacity for cellulose degradation, whereas S. fibuligera ME8 exhibited enhanced capabilities for protein and starch degradation. This study provides a theoretical reference for the application of yeast in the fermentation of sauce-flavor Baijiu.

Dynamics of the microbiome and volatile organic compounds during fermentation and aging of soy sauce

A comprehensive analysis of the microbiome and volatile organic compounds (VOC) in the moromi of soy sauce during fermentation and aging was conducted under industrial production. Microbiome analysis using next-generation sequencing revealed the presence and dynamics of microorganisms other than Aspergillus, Tetragenococcus, Zygosaccharomyces, and Wickerhamiella, which were used as starters. The bacterial community of the moromi on the first day of this process was rich in diversity. Staphylococcus, Bacillus, Kurthia, Acinetobacter, Enterococcus, and Macrococcus that grew during koji making were relatively dominant. However, as the fermentation progressed, only Tetragenococcus became dominant in the bacterial communities. In contrast, the fungal community was simple at the beginning of fermentation and aging, with Aspergillus present almost exclusively. After adding Zygosaccharomyces rouxii on day 42, the fungal community changed significantly. At the end of fermentation and aging, the fungal community diversified, with Millerozyma, Wickerhamiella, Yamadazyma, and Saccharomycopsis becoming dominant. The analysis of VOC showed that the VOC profile changed during fermentation and aging, and that the VOC profile changed significantly after adding Z. rouxii. The correlation analysis between the microbiome and VOC showed that Wickerhamiella, Millerozyma, Debaryomyces, Yamadazyma, and Candida had a significant positive correlation with alcohols, esters, and phenols produced in the later stage of fermentation and aging, indicating that not only Z. rouxii but also various fungi may contribute to the formation of the complex aroma profile of soy sauce.

Evolution of fermented grain yeast communities in strong-flavored baijiu and functional validation of yeasts that produce superior-flavored substances

BACKGROUND

Baijiu is a well-known alcoholic beverage in China and the quality is determined by various microorganisms during the fermentation process. Yeast is one of the most important microorganisms in the fermentation of baijiu. It has a strong esterification capacity and also affects the aroma.

RESULTS

High-throughput sequencing results showed that the fermented grains (jiupei) during baijiu production were mainly composed of eight highly abundant yeast species. The species and abundance of yeasts changed significantly with the fermentation process. The flavor of 30 yeast strains in the jiupei was determined by a sniffing test and gas chromatography-mass spectrometry (GC-MS). The strain with the highest flavor substance content (2.34 mg L-1), named YX3205, was identified as Clavispora lusitaniae. Tolerance results showed that C. lusitaniae YX3205 can tolerate up to 15% (v v-1) ethanol. In a solid-state simulated fermentation experiment, the content of 24 flavor substances was significantly increased in the fortified group, and the total ester content reached 4240.73 μg kg-1, which was 2.8 times higher than that of the control group.

CONCLUSION

The present study demonstrated the potential of C. lusitaniae YX3205 to enhance the flavor of baijiu, thereby serving as a valuable strain for the improvement of the flavor quality of baijiu. © 2024 Society of Chemical Industry.

Strategies and Challenges of Microbiota Regulation in Baijiu Brewing

The traditional Chinese Baijiu brewing process utilizes natural inoculation and open fermentation. The microbial composition and abundance in the microecology of Baijiu brewing often exhibit unstable characteristics, which directly results in fluctuations in Baijiu quality. The microbiota plays a crucial role in determining the quality of Baijiu. Analyzing the driving effect of technology and raw materials on microorganisms. Elucidating the source of core microorganisms and interactions between microorganisms, and finally utilizing single or multiple microorganisms to regulate and intensify the Baijiu fermentation process is an important way to achieve high efficiency and stability in the production of Baijiu. This paper provides a systematic review of the composition and sources of microbiota at different brewing stages. It also analyzes the relationship between raw materials, brewing processes, and brewing microbiota, as well as the steps involved in the implementation of brewing microbiota regulation strategies. In addition, this paper considers the feasibility of using Baijiu flavor as a guide for Baijiu brewing regulation by synthesizing the microbiota, and the challenges involved. This paper is a guide for flavor regulation and quality assurance of Baijiu and also suggests new research directions for regulatory strategies for other fermented foods.

Analysis of ester-producing performance in high-yield ethyl hexanoate yeast and the effect on metabolites in bio- enhanced Daqu, the starter for Baijiu and other traditional fermented foods

AIMS

Ethyl hexanoate, one of the key flavor compounds in strong-flavor Baijiu. To improve the content of ethyl hexanoate in strong-flavor Baijiu, a functional strain with high yield of ethyl hexanoate was screened and its ester-producing performance was studied.

METHODS AND RESULTS

Upon identification, the strain was classified as Candida sp. and designated as ZY002. Under optimal fermentation conditions, the content of ethyl hexanoate synthesized by ZY002 can be as high as 170.56 mg L-1. A fermentation test was carried out using the ZY002 strain bioaugmented Daqu to verify the role of the strain applied to Baijiu brewing. It was found that strain ZY002 could not only improve the moisture and alcohol contents of fermented grains but also diminish the presence of reducing sugar and crude starch. Furthermore, it notably amplified the abundance of flavor compounds.

CONCLUSION

In this study, Candida sp. ZY002 with a high yield of ethyl hexanoate provided high-quality strain resources for the actual industrial production of Baijiu.

Airborne microorganisms and key environmental factors shaping their community patterns in the core production area of the Maotai-flavor Baijiu

Airborne microorganisms are important parts of the Moutai-flavor Baijiu brewing microbial community, which directly affects the quality of Baijiu. However, environmental factors usually shape airborne microbiomes in different distilleries, even in the different production areas of the same distillery. Unfortunately, current understanding of environmental factors shaping airborne microbiomes in distilleries is very limited. To bridge this gap, we compared airborne microbiomes in the Moutai-flavor Baijiu core production areas of different distilleries in the Chishui River Basin and systematically investigated the key environmental factors that shape the airborne microbiomes. The top abundant bacterial communities are mainly affiliated to the phyla Actinobacteriota, Firmicutes, and Proteobacteri, whereas Ascomycota and Basidiomycota are the predominant fungal communities. The Random Forest analysis indicated that the biomarkers in three distilleries are Saccharomonospora and Bacillus, Thermoactinomyces, Oceanobacillus, and Methylobacterium, which are the core functional flora contributing to the production of Daqu. The correlation and network analyses showed that the distillery age and environmental temperature have a strong regulatory effect on airborne microbiomes, suggesting that the fermentation environment has a domesticating effect on air microbiomes. Our findings will greatly help us understand the relationship between airborne microbiomes and environmental factors in distilleries and support the production of the high-quality Moutai-flavor Baijiu.