传统醋曲储存过程中的微生物多样性

Microbial diversity of traditional vinegar Daqu during storage

摘要:

【背景】醋曲是我国传统谷物醋酿造中的重要微生物来源，通常一次制备分批使用。【目的】解析传统醋曲储存过程中微生物群落结构变化规律。【方法】从山西晋南一家百年老醋坊分别采集大曲原料、新制醋曲、储存7个月和12个月的醋曲，利用高通量测序技术分析微生物多样性。【结果】从4组样品中共找到610个真菌可操作分类单元(operational taxonomic unit, OTU)和747个细菌OTU。子囊菌门(Ascomycota，占比95%)和厚壁菌门(Firmicutes，占比81%)分别为优势的真菌和细菌类群。醋曲成品中约1/3的真菌OTU和约95%的细菌OTU可在醋曲原料中找到，说明原料是醋曲的重要微生物来源。相较于新制醋曲，储存7个月和12个月醋曲中的真菌和细菌多样性均显著降低。醋曲贮存过程中微生物群落结构发生明显改变，并且相较于真菌群落结构，细菌群落结构更易波动。相较于醋曲原料，醋曲成品中显著富集扣囊复膜孢酵母(Saccharomycopsis fibuligera)、东方伊萨酵母(Issatchenkia orientalis)等真菌，以及克罗彭斯特菌属(Kroppenstedtia)细菌。功能预测发现，醋曲中的真菌以腐生营养型为主，细菌与代谢相关的通路显著富集。【结论】醋曲贮存过程中微生物多样性降低，微生物群落结构也随之发生变化。研究结果提高了对传统醋曲中微生物来源及其群落结构变化规律的认识，为稳定大曲品质及其工艺改良提供了科学依据。

Abstract:

[Background] Vinegar Daqu is an important source of microorganisms during the brewing of traditional grain vinegar in China. It is usually prepared once and used in batches. [Objective] To reveal the structural variations of the microbial community in the traditional vinegar Daqu during the long-term storage. [Methods] From a century-old vinegar factory in southern Shanxi, we collected the raw materials of Daqu and the vinegar Daqu products that were newly produced and had been stored for 7 and 12 months, respectively. Microbial diversity was investigated by high-throughput DNA sequencing. [Results] A total of 610 fungal operational taxonomic units (OTUs) and 747 bacterial OTUs were obtained from the four groups of samples. Ascomycota (95%) and Firmicutes (81%) were dominant among fungi and bacteria, respectively. About one third of fungal OTUs and 95% of bacterial OTUs in vinegar Daqu were detected in the raw materials of Daqu, indicating that raw materials acted as the main source of microorganisms in vinegar Daqu. Compared with that in the newly-produced vinegar Daqu, the diversity of fungi and bacteria decreased significantly in vinegar Daqu samples that have been stored for 7 months and 12 months. Microbial community structure changed during the storage of vinegar Daqu, with the bacterial community structure being more prone to fluctuation than the fungal community. Compared with those in the raw materials, fungi like Saccharomycopsis fibuligera and Issatchenkia orientalis and bacteria such as Kroppenstedtia were significantly enriched in vinegar Daqu products. According to the results of function prediction, the fungi were mainly saprotrophic, and the metabolism pathways of bacteria were enriched significantly. [Conclusion] Vinegar Daqu presented decreased microbial diversity and varied microbial community structure during the long-term storage. This study enriched our understanding of the microorganism source in traditional vinegar Daqu and the variation patterns of microbial community structure in vinegar Daqu during storage, providing a scientific basis for stabilizing Daqu quality and improving the production process.