Changes Of Bacterial Diversity And Organic Acids During Fermentation Of Northeast Sauerkraut

Northeast sauerkraut is one of the iconic fermentation products in Northeast China.In the natural fermentation process of the Northeast sauerkraut,a variety of microorganisms from raw materials,containers and fermentation environments use the cabbage raw material as a carrier to reproduce and metabolize during the fermentation process,thereby producing a variety of flavor substances.During the fermentation process,the microbial community will change the composition and content of the flavor substances of the product as the fermentation environment changes,which will affect the sensory quality of the product.Organic acid is one of the important taste substances in the Northeast sauerkraut.Traditionally,the acid in the Northeast sauerkraut is lactic acid,but a variety of organic acids are produced during the fermentation process.The sour taste of the Northeastern sauerkraut is unique and pleasant,which has a great relationship with the existence of various organic acids produced during the fermentation process.Therefore,the study on the bacterial diversity and the change of organic acids in the natural fermentation process of sauerkraut in Northeast China,and the effects of the types and contents of organic acids on the acidity of the products were studied,which was essential for the formation of high-quality sauerkraut products with good flavor and high quality.In this study,the Northeast sauerkraut of three fermentation batches with different fermentation time was used as the research object.16 S r RNA amplicon sequencing and high performance liquid chromatography was used to study the bacterial diversity,organic acid species and content changes of Northeastern sauerkraut during the natural fermentation.Temporal dominance of sensations(TDS)was used to evaluate the acid perception of Northeast sauerkraut.The purpose was to clarify the effects of organic acids on the acid perception of Northeast sauerkraut.The results showed that:(1)During the fermentation process of Northeast sauerkraut,the bacteria we re rich in species,and the species diversity decreased first and then increased.The species richness and evenness increased first and then decreased.(2)At the level of phylum,the main bacteria in the samples of different fermentation time of Northeastern sauerkraut are Firmicutes and Proteobacteria.At the genus level,Lactobacillus and Pediococcus were detected in different fermentation times of Northeast sauerkraut.Lactobacillus always has an advantage in different fermentation time of Northeast sau erkraut,and its content is more than other genus.It plays a major role in the bacterial flora of Northeast sauerkraut and is the main dominant flora in Northeast sauerkraut.Pediococcus has a certain amount in different fermentation time of Northeast sauerkraut,which is more stable than other flora in the whole fermentation cycle of Northeast sauerkraut.It is also one of the main genus in the fermentation process of Northeast sauerkraut.(3)The main organic acid produced in the fermentation process of Northeast sauerkraut is lactic acid,but it can also produce 8 kinds of organic acids such as citric acid,acetic acid,oxalic acid,malic acid,succinic acid,tartaric acid,propionic acid and valeric acid.The content of lactic acid,acetic acid,citric acid,oxalic acid,malic acid,succinic acid and tartaric acid increased with the fermentation time during the fermentation process.The content increased rapidly at 30 d-90 d,and increased slowly at 90 d-120 d.Propionic acid and valeric acid were detected at 120 d of fermentation.(4)Correlation between bacterial diversity and organic acids in Northeast sauerkraut showed that Lactobacillus and Pediococcus may be related to the production of lactic acid,succinic acid,oxalic acid,citric acid,malic acid,tartaric acid and acetic acid;in addition,Pediococcus may also be related to the production of propionic acid and valeric acid.(5)The composition and content of organic acids are different,which directly leads to different acidity of the products.The dominant acid perception was weak at 30 days and 60 days of fermentation,and the dominant rate was higher at 30 days of fermentation;the dominant acid perception was mild at 90 days of fermentation;and the dominant acid perception was acerbic at 120 days of fermentation.The content of organic acids was the most suitable for 90 days fermentation of Northeast sauerkraut.The main dominant acid perception of the final product was mild.It was suggested that 90 days should be the fermentation period of Northeast sauerkraut.(6)Lactic acid played a dominant role in the formation of sourness in Northeast sauerkraut,while citric acid,acetic acid,oxalic acid,malic acid,succinic acid and tartaric acid played an auxiliary role.The correlation analysis showed that these organic acids could promote the acid perception of mild of Northeast sauerkraut when the content was appropriate,but the acid perception of mild would be destroyed when the content was not appropriate.The presence of propionic acid and valeric acid could lead to the acid perception of acerbic of Northeast sauerkraut.