Study On The Correlation Between Bacterial Diversity And Biogenic Amine Evolution In The Fermentation Process Of Sauerkraut

Sauerkraut is made from fresh vegetables by spontaneous or inoculated fermentation.It is a typical representative of traditional fermented food in China.Affected by climate,customs and eating habits,Chinese sauerkraut have formed Sichuan pickles,Jiangxi pickles and northeast sauerkraut with classic characteristics due to different materials and processes.Northeast sauerkraut takes Chinese cabbage as raw material.The traditional technology is based on the spontaneous fermentation of low temperature weather in the north under low salinity for more than 30 days.The complex composition of flora in spontaneous fermentation sauerkraut,and easy to be polluted by exogenous spoilage microorganisms make it difficult to control microbial harmful factors such as biogenic amines and nitrites.Compared with spontaneous fermentation,inoculated fermentation has the advantages of short fermentation time,stable quality,high safety and less affected by seasons.At present,northeast sauerkraut is in the transition period from traditional spontaneous fermentation to industrialized direct fermentation.Green,safe and high-quality inoculated fermentation with lactic acid bacteria is the only way for the upgrading of pickled cabbage industry in Northeast China.In this paper,the self screened Lactobacillus plantarum SC-5 with excellent fermentation performance was used as a control between inoculated fermented and spontaneous fermented sauerkraut.The flora succession of sauerkraut during fermentation was analyzed by high-throughput sequencing,and the metabolic kinetics of biogenic amines and flavor substances in sauerkraut were dynamically detected by high-performance liquid chromatography and GC-MS.finally,the correlation between metabolites and flora was analyzed by multivariate statistics.The main research results of this paper are as follows:(1)Analysis of flora diversity: The results of 16S rDNA high-throughput sequencing showed that the flora richness was the highest at 15 days,then decreased,and the flora richness was the lowest at 60 days.Firmicutes and Protebacteria are the two main phyla in spontaneous and inoculated fermention sauerkraut.At the genus level,Lactobacillus was always dominant in inoculated fermention sauerkraut,and had a significant negative correlation with salinity.A total of 70 lactic acid strains were obtained,involving Lactobacillus,Lactoccus,Leuconostoc,Enterococcus,Streptococcus,Weissella,Pediococcus.;Acinetobacter,Pseudomonas and Enterobacteriaceae unclassified are the main non lactic acid bacteria in the early stage of fermentation.In the late stage of fermentation,the relative abundance of Citrobacter was dominant.(2)Determination of metabolic dynamics of biogenic amines: Putrescine,tyramine,spermidine,cadaverine and histamine were determined by high performance liquid chromatography(HPLC).With the progress of fermentation,the content of total amine increased.The contents of total amine in spontaneous fermentation and inoculated fermentation sauerkraut were 234.62 ? 266.81,216.72 ?237.33 mg/kg respectively,the content of total amine in fermented sauerkraut inoculated with 1.5% and 2.5% Na Cl was significantly lower than that in spontaneous fermentation(p < 0.05).The amine(except tyramine)content of inoculated fermentation sauerkraut was lower than that of spontaneous fermentation sauerkraut,but the tyramine content increased significantly(p < 0.05).Salinity had no significant effect on biogenic amines.According to Spearman rank correlation test,Lactobacillus plantarum SC-5 was significantly negatively correlated with tyramine,cadaverine and putrescine(-0.43 < R <-0.38).In addition,six common non lactic acid bacteria Shewanella(0.72 < R < 0.79),Alcaligenes(0.67 < R < 0.73),provincia(0.75 < R <0.80),Microvirgula(0.58 < R < 0.64),Citrobacter(R?0.74)and Enterobacteriaceae(0.43 < R < 0.50)were positively correlated with tyramine,cadaverine and putrescine.(3)Evolution law of organic acids:The contents of lactic acid,citric acid,acetic acid,oxalic acid and tartaric acid in sauerkraut were determined by high performance liquid chromatography(HPLC).Lactic acid is the main factor in the formation of acid sensitivity in northeast sauerkrau,and the content of lactic acid is the highest in organic acid.The lactic acid content of inoculated fermentation sauerkraut under three salinities reaches the peak value of 17.81 ± 0.80,18.59 ± 0.36 and 19.19 ± 0.33 g/kg in 30 days,which is the key period of lactic acid production.The final content of lactic acid in sauerkraut with1.5% salinity was the highest,18.19 ± 0.85 g/kg.The content of citric acid increased gradually,and the content of citric acid was rich in sauerkraut with 2.5% salinity for60 days,which was 2.96 ± 0.2 g/kg.Acetic acid was first produced on the 7th day of fermentation.After 60 days of fermentation,the content of acetic acid was 1.23 ± 0.04,0.87 ± 0.05 and 1.88 ± 0.21 g/kg;The contents of oxalic acid and tartaric acid are slightly lower,which can improve the acid sensitivity.(4)Analysis of volatile flavor components:The volatile flavor of inoculated fermented sauerkraut for 15 days,30 days and45 days was analyzed by headspace solid phase microextraction(HS-SPME)and gas chromatography(GC-MS).Eight kinds of volatile flavor substances including esters,isothiocyanates,ketones,aldehydes,acids,nitriles,ethers and sulfides were detected.The content of acids was high in 15 days,accounting for 53.73%;The content of alcohol was the highest in 30 and 45 days,with the relative content of 28.18% and31.87%.The content of some short chain fatty acids beneficial to human body,such as butyric acid 2.67%,is the most abundant after 45 days of fermentation.Conclusion: This study provides a theoretical basis for ensuring high-quality lactic acid bacteria to inoculated fermentation sauerkraut.