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图2展示了不同发酵时期游离氨基酸含量的变化，其含量由发酵初期的114.294 mg/100 mL增加至发酵末期的897.382 mg/100 mL。在发酵过程中，谷氨酸、丙氨酸、精氨酸和亮氨酸含量较高，约占总游离氨基酸的50%。
在门水平上，厚壁菌门、变形菌门、子囊菌门、担子菌门和毛霉菌门为优势菌门。在属水平上，共鉴定出14个优势属，包括乳酸杆菌属、醋酸杆菌属、梭状芽孢杆菌属、肠杆菌属、明串珠菌属、克雷伯氏菌属、片球菌属、酵母菌属、横梗霉属、毕赤酵母属、曲霉属、红曲霉属、丝衣霉属和异常威克汉姆酵母属。分型分析结果将整个发酵阶段分成了两种类型，类型1 包括V1和V2阶段，类型2 包括V3和V4阶段（图3）。
宏基因组数据经过滤和处理后，将非冗余基因在KEGG数据库中进行比对，获得对应的注释概况并进行统计。结果表明大多数基因参与代谢途径，且主要与碳水化合物代谢和氨基酸代谢有关（图4a）。此外，乳酸杆菌属、醋酸杆菌属和酵母菌属主要贡献碳水化合物和氨基酸的代谢活动。如图4b-c所示，乳酸杆菌属、醋酸杆菌属和酵母菌属对碳水化合物代谢途径的贡献分别为43.12%～73.75%、10.60%～45.54%和72.29%～88.58%，对氨基酸代谢途径的贡献分别为29.28%～69.21%、15.44%～61.63%和73.38%～88.28%。
通过参考KEGG数据库，并根据非冗余基因编码的酶和发酵过程中检测到的游离氨基酸构建代谢途径。如图5所示，原料中的大分子物质（蛋白质、淀粉）通过一系列酶的作用合成各种游离氨基酸和一些风味前体物质。
基于重构的代谢途径，进一步评估了不同微生物在底物降解、氨基酸合成及风味前体物质合成途径中的分布（图6）。结果显示，乳酸杆菌属、梭状芽胞杆菌属、克雷伯菌属、明串珠菌属、片球菌属和酵母属是底物降解途径中的主要贡献微生物，表明这些微生物具有较强的底物分解潜力。醋酸杆菌属、乳酸杆菌属、梭状芽胞杆菌属、肠杆菌属和酵母菌属与氨基酸合成密切相关。酵母菌属、醋酸杆菌属、梭状芽孢杆菌属、曲霉属、肠杆菌属、克雷伯氏菌属、乳酸杆菌属、明串珠菌属、横梗霉属和片球菌属主要贡献风味前体物质的合成。
Metagenomic analysis revealing the metabolic role of microbial communities in the free amino acid biosynthesis of Monascus rice vinegar during fermentation
Hang Gaoa, Jian Zhanga, Li Liua, Lijun Fua, Yan Zhaoa, Germán Mazzab, Xin Zhanga,*
a Beijing Academy of Food Sciences, 100068 Beijing, China
b Institute for Research and Development in Process Engineering, Biotechnology and Alternative Energies, (PROBIEN, CONICET-UNCo), 8300 Neuquén, Argentin
*Corresponding author.
Abstract
Free amino acid (FAA) is the important component of vinegar that influences quality perception and consumer acceptance. FAA is one of the major metabolites produced by microorganisms; however, the microbial metabolic network on FAA biosynthesis remains unclear. Through metagenomic analysis, this work aimed to elucidate the roles of microbes in FAA biosynthesis during Monascus rice vinegar fermentation. Taxonomic profiles from functional analyses showed 14 dominant genera with high contributions to the metabolism pathways. The metabolic network for FAA biosynthesis was then constructed, and the microbial distribution in different metabolic pathways was illuminated. The results revealed that 5 functional genera were closely involved in FAA biosynthesis. This study illuminated the metabolic roles of microorganisms in FAA biosynthesis and provided crucial insights into the functional attributes of microbiota in vinegar fermentation.
GAO H, ZHANG J, LIU L, et al. Metagenomic analysis revealing the metabolic role of microbial communities in the free amino acid biosynthesis of Monascus rice vinegar during fermentation[J]. Food Science and Human Wellness, 2024, 13(4): 2317-2326. DOI:10.26599/FSHW.2022.9250193.
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