Abstract
BackgroundChinese strong-flavor baijiu (CSFB), one of the three major baijiu types, is the most popular baijiu type among consumers in China. A variety of microbes are involved in metabolizing raw materials to produce ethanol and flavor substances during fermentation, which fundamentally determined the quality of baijiu. It is of great importance to study microbial community of fermented grains (zaopei) during baijiu brewing process for improving its quality. In this study, we firstly used propidium monoazide (PMA) to treat zaopei samples from 5-year pit and 20-year pit for removing the interference of non-viable fungi, and analyzed the diversity of total fungi and viable fungi by quantitative PCR (qPCR) and high-throughput sequencing (HTS) based on ITS2 gene.ResultsThe results showed that total fungi and viable fungi displayed no significant differences at OTU, phylum, or genus levels during fermentation within two kinds of pits. A total of 6 phyla, 19 classes, and 118 genera in fungi were found based on OTUs annotation in zaopei samples from 5-year pit and 20-year pit. Besides, non-viable fungi had little effect on the fungal community diversity during the fermentation cycle. It was found that the most dominant viable fungi belonged to Saccharomyces, Kazachstania, Naumovozyma, and Trichosporon, and Naumovozyma was firstly detected in zaopei samples of CSFB. Moreover, based on the variation of flavor substances in zaopei samples, the quality of CSFB produced from older pit was better than that produced from younger pit.ConclusionThe non-viable fungi had little effect on the fungal diversity, structure, and relative abundance in zaopei samples of CSFB, and Naumovozyma was firstly detected in zaopei samples of CSFB. Our findings can be applied as guidance for improving the quality and stability of CSFB.
Highlights
Chinese baijiu, a historic alcoholic beverage, is distilled from spontaneously solid-state fermented grains
A same tendency was shared in zaopei samples from these two kinds of pits, which kept increasing from day 7 to day 60 (Fig. 3B)
The flavor compounds in zaopei played a key influence on the quality of baijiu, the content of acetic acid, lactic acid, butyric acid, ethyl acetate, ethyl lactate and ethyl caproate were detected during the total fermentation cycle
Summary
A historic alcoholic beverage, is distilled from spontaneously solid-state fermented grains. Because of the fragrant flavor, soft mouthfeel, and long-lasting aftertaste in Chinese strong-flavor baijiu (CSFB) [1], it is very popular among consumers, and its production is the highest in. After distillation of the zaopei (fermented grains), ethanol, flavor compounds and water are collected together for storage and blending to produce final product-CSFB (Fig. 1). Many microorganisms from daqu and pit mud are involved in the solidstate fermentation, during which nutrient substances in grains were consumed for quick proliferation and producing ethanol and flavor compounds [1,2,3]. A variety of microbes are involved in metabolizing raw materials to produce ethanol and flavor substances during fermentation, which fundamentally determined the quality of baijiu. It is of great importance to study microbial community of fermented grains (zaopei) during baijiu brewing process for improving its quality. We firstly used propidium monoazide (PMA) to treat zaopei samples from 5-year pit and 20-year pit for removing the interference of non-viable fungi, and analyzed the diversity of total fungi and viable fungi by quantitative PCR (qPCR) and high-throughput sequencing (HTS) based on ITS2 gene
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