Abstract
Fermentation microbiota is specific microorganisms that generate different types of metabolites in many productions. In traditional solid-state fermentation, the structural composition and functional capacity of the core microbiota determine the quality and quantity of products. As a typical example of food fermentation, Chinese Maotai-flavor liquor production involves a complex of various microorganisms and a wide variety of metabolites. However, the microbial succession and functional shift of the core microbiota in this traditional food fermentation remain unclear. Here, high-throughput amplicons (16S rRNA gene amplicon sequencing and internal transcribed space amplicon sequencing) and metatranscriptomics sequencing technologies were combined to reveal the structure and function of the core microbiota in Chinese soy sauce aroma type liquor production. In addition, ultra-performance liquid chromatography and headspace-solid phase microextraction-gas chromatography-mass spectrometry were employed to provide qualitative and quantitative analysis of the major flavor metabolites. A total of 10 fungal and 11 bacterial genera were identified as the core microbiota. In addition, metatranscriptomic analysis revealed pyruvate metabolism in yeasts (genera Pichia, Schizosaccharomyces, Saccharomyces, and Zygosaccharomyces) and lactic acid bacteria (genus Lactobacillus) classified into two stages in the production of flavor components. Stage I involved high-level alcohol (ethanol) production, with the genus Schizosaccharomyces serving as the core functional microorganism. Stage II involved high-level acid (lactic acid and acetic acid) production, with the genus Lactobacillus serving as the core functional microorganism. The functional shift from the genus Schizosaccharomyces to the genus Lactobacillus drives flavor component conversion from alcohol (ethanol) to acid (lactic acid and acetic acid) in Chinese Maotai-flavor liquor production. Our findings provide insight into the effects of the core functional microbiota in soy sauce aroma type liquor production and the characteristics of the fermentation microbiota under different environmental conditions.
Highlights
The microbiota in natural environments is complex and often includes thousands of genera from a diverse range of species (Astudillo-Garcia et al, 2017)
The production rate of acids increased from days 20 to 30, with the average ranging from −0.34 to 4.91 for acids generally (Figure 1C) and −0.01 to 2.17 for lactic acid and acetic acid (Figure 1D)
Compared with previous studies (Wu et al, 2013; Chen et al, 2014), we found that 11 bacterial genera and 10 fungal genera were the core microbiota in the microbial succession of liquor production, which affected the production of flavor components (Figures 2A,B)
Summary
The microbiota in natural environments is complex and often includes thousands of genera from a diverse range of species (Astudillo-Garcia et al, 2017). In natural environments or under artificially controlled conditions, fermentation microbiota have the potential to use different raw materials to produce a variety of metabolites (Xu and Ji, 2012; Lu et al, 2016; Wang et al, 2016) They are commonly characterized by the presence of specific microorganisms, orderly microbial succession and an unusual functional shift (Azwar et al, 2014; Di Cagno et al, 2014; Kong et al, 2014; Qi et al, 2014). Species were isolated and identified from food fermentation processes by culture-dependent and independent techniques (Papalexandratou et al, 2013; Chen et al, 2014; Ricciardi et al, 2015) These studies gained some insight into the microbial populations, our knowledge about the core structural microbiota in fermented foods remain limited (Wu et al, 2013). In soy sauce fermentation, 22 frequent genera have been reported to be candidates of the core microbiota (Sulaiman et al, 2014)
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