臭豆腐发酵过程中丙酸形成的机制

The Mechanisms of Propionic Acid Formation in the Fermentation of Stinky Tofu

为探究臭豆腐发酵过程中丙酸产生的原因及机制,采用宏基因组学对卤水和臭豆腐中微生物组成进行分析鉴定。与丙酸含量极低的“对照卤水”相比,1号臭豆腐卤水中产丙酸的丙酸杆菌属种类和丰度整体上升,其中丙酸杆菌科细菌NML_160184的丰度上升7.6倍,产酸丙酸杆菌的丰度上升4.7倍,丙酸杆菌_细菌的丰度上升3.8倍。与2号臭豆腐相比,1号成品豆腐中产丙酸的丙酸杆菌属种类和丰度也显著增加,丙酸杆菌科细菌P6A17的丰度上升59.4倍,未分类丙酸杆菌科的丰度上升54.9倍,丙酸杆菌_细菌的丰度上升47倍,假丙酸杆菌_massiliense的丰度上升29.7倍。采用非靶向代谢组学分析卤水中微生物代谢产物和功能,结果发现不同卤水的微生物组成的代谢活动有显著差异,臭豆腐中丙酸水平的差异极有可能是受卤水中微生物的种类和代谢活动的影响。结论:臭豆腐中检出丙酸是因发酵过程中微生物自然产生而非人为添加,不同来源的卤水产丙酸菌的种类和丰度也不同,最后产品的丙酸含量也会呈现显著差异。

The content of propionic acid in No.1 stinky tofu detected by HPLC was about 1.32 mg/g,which was higher than the content of propionic acid in No.2 stinky tofu from different manufacturers(0.56 mg/g),and the content of propionic acid in tofu embryos before fermentation was very low,about 0.026 mg/g,but the content of propionic acid in brine was as high as 6.35 mg/mL.As a food additive,propionic acid must be marked on the packaging if it is added during the production process,but the No.1 stinky tofu manufacturer did not artificially add propionic acid.Therefore,this experiment aimd to explore the causes and mechanisms of production of propionic acid during the fermentation of stinky tofu.Using metagenomics to analyze and identify the microbial composition in brine and stinky tofu,it was found that compared with the'control brine'with very low propionic acid content,the species and abundance of Propionibacterium that produced propionic acid in No.1 stinky tofu brine increased overall.Among them,the abundance of Propionibacteriaceae_bacterium_NML_160184 had increased by 7.6 times,the abundance of Acidipropionibacterium_acidipropionici acidigenes has increased by 4.7 times,and the abundance of Propionibacterium_bacteria has increased by 3.8 times.Compared with No.2 stinky tofu,the species and abundance of Propionibacterium producing propionic acid in No.1 finished tofu also increased significantly.The abundance of Propionibacteriaceae_bacterium P6A17 increased by 59.4 times,and the abundance of unclassified_f_Propionibacteriaceae increased by 54.9 times.The abundance of Propionibacteriales_bacterium increased by 47 times,and the abundance of Pseudopropionibacterium_massiliense increased by 29.7 times.Non-targeted metabolomics analysis of the microbial metabolites and functions in brine found that the metabolic activities of different brine microbial compositions were significantly different.The difference in propionic acid levels in stinky tofu was most likely due to the types and metabolic activities of the microorganisms in the brine.In summary,the detection of propionic acid in stinky tofu was due to the natural production of microorganisms during the fermentation process rather than artificial addition.Due to the different types and abundance of propionic acid-producing bacteria in brines from different sources,the propionic acid content of the final product will also showed significant differences.