Analysis Of Microbial Flora And Flavor Substances In Sour Bamboo Shoots Of Liuzhou River Snails Rice Noodle

Sour bamboo shoot is a traditional Chinese fermented vegetable food.It is made from fresh bamboo shoots through natural fermentation.It is very popular among consumers because of its good storage and unique flavor after fermentation.The lactic acid bacteria in the sour bamboo shoots not only have the function of probiotics,but also produce rich volatile flavor substances,organic acids,etc.,which give the sour bamboo shoots a unique flavor.With the popularity of snail powder all over the world,the market share of sour bamboo shoots is gradually expanding,which is an important excipient of snail powder.However,according to the investigation,the production of sour bamboo shoots is still mainly concentrated in small family workshops at this stage.Therefore,exploring the flavor substances and excellent strains of sour bamboo shoots in Liuzhou river snails rice noodle will help the large-scale and standardized production of sour bamboo shoots,It is great significance to improve the quality of Liuzhou river snails rice noodle and build a brand of Liuzhou river snails rice noodle.In this paper,the naturally fermented bamboo shoots were taken as the object of study,the nutritional composition、volatile flavor substances and microbial diversity of sour bamboo shoots in different stages of natural fermentation were studied.Compared the natural fermentation and inoculation fermented sour bamboo shoots flavor difference.The contents and results of the experiment were as follows:（1）Analysis of the nutritional components of bamboo shoots in different stages of fermentation:With the extension of fermentation time,the protein and total sugar content of bamboo shoots decreased gradually,and the protein content decreased by 14.03%in the middle fermentation stage and 34.39%in the late fermentation stage;The content decreased by 22.22%,and decreased by 38.89%at the end of fermentation.While the content of dietary fiber increased by 33.33%during the fermentation process.The content of each mineral showed a declining trend with the extension of fermentation time,among which the content of manganese decreased most obviously.The content of zinc decreased by 86.64%,followed by the content of zinc decreased by 76.65%,the content of other elements also decreased by 50%～70%,the content of iron decreased the least,decreased by 39.53%.the content of selenium was low before fermentation,no selenium was detected after fermentation.Among the 17 kinds of amino acids in fresh Dendrocalamus latiflorus,the content of glutamic acid was relatively high,the second was aspartic acid,and the least was cystine..The contents of all amino acids decreased to different degrees after fermentation,among which arginine decreased by 78.71%.（2）Microbial diversity analysis of sour bamboo shoots in different stages of fermentation:The bacterial flora in sour bamboo shoots of natural fermentation 1 d,15 d,30 d and 45 d were determined by high-throughput sequencing.The results of Alpha diversity showed that the abundance of strains was increased with the extension of fermentation time,and the diversity of strains became more abundant.At the phylum level,the abundance of Firmicutes and Actinobacteria was increased with the extension of fermentation time,while the abundance of Cyanobacteria and Proteobacteria was decreased.At the genus level,the dominant bacteria in the early fermentation samples included Lactococcus,Weissella,and Enterobacteriaceae.The guiding bacteria in the middle fermentation samples were Lactobacillus,Lactococcus,Weisseria,Pediococcus.The dominant bacteria in the sour bamboo shoot samples at the end of fermentation were mainly Lactobacillus.By compared the content changes of lactic acid bacteria in the fermentation process,it could be preliminarily speculated that Lactobacillus was dominant in the fermentation process of sour bamboo shoots,and Lactococcus and Weisseria played an important part in the early fermentation stage.（3）Screening of excellent lactic acid bacteria:30 strains of lactic acid bacteria were screened from naturally fermented sour bamboo shoots,and 26 strains of lactic acid bacteria were identified by Gram staining and 16S rRNA sequencing,which belonged to the genus Lactobacilli and Pediococcus respectively,A total of 4 species,named Lactiplantibacillus plantarum,Leviactobacillus brevis,Pediococcus acidilactici,and P.pentosaceus.The Lactobacillus plantarum R1 strain had the strongest acid-producing ability,and the acid-producing rate was as high as 2.3%.The nitrite degradation rate of Pediococcus lactis R9 was as high as 99.9%through the nitrite reduction experiment.Therefore,these two strains were selected for subsequent fermentation.R1 was in logarithmic growth phase from 1 h to 12 h,and R9 was in logarithmic growth phase from 1 h to 24 h by measuring the growth curve.Therefore,after cultured the lactic acid bacteria for 12 h,the bacterial liquid could be inserted into bamboo shoots for fermentation.（4）Analysis of flavor components of sour bamboo shoots in different stages of fermentation:Eighty-eight volatile flavor compounds were isolated and identified from bamboo shoots fermentation by HS-SPME-GC-MS.The main volatile components of sour bamboo shoots in the middle and late fermentation stages were phenols and acids.Fifty-five volatile substances were detected in lactic acid bacteria inoculated and fermented sour bamboo shoots.By selective ion scanning（SIM）mode in gas chromatography-mass spectrometry（GC-MS）,only p-cresol and 2-methoxy-5-methylphenol were detected in the acid bamboo shoot samples,which was not detected in other fermented vegetables.It could be inferred that p-cresol and 2-methoxy-5-methylphenol were the unique flavor substances of sour bamboo shoots.The result of the pearson correlation coefficient showed that Lactobacillus and Lactococcus were positively correlated with most of the characteristic flavor substances in the fermentation process;Candidatus saccharimonas,Clostridium_sensu_stricto₁,Staphylococcus and other genera were negatively correlated with characteristic flavor substances such as n-hexano、2-（octadecyloxy）ethanol and ethyl caprylate.The content of p-cresol was the highest in fermented sour bamboo shoots,which was positively correlated to Saccharomonas,Clostridium stricture,Pediococcus,Leuconostoc and Staphylococcus.Compared with natural fermentation,the contents of esters,aldehydes and ketones in inoculated fermentation increased significantly,and the contents of alkanes and olefins increased slightly.While ethers and phenols were significantly reduced,the content of dimethyl ether decreased from 6.234%to 3.552%,the content of phenol decreased from 16.511%to 0.908%,and the content of p-cresol increased slightly.Acids were slightly reduced,and alcohol content was almost indistinguishable.However,2-methoxy-5-methylphenol was not detected in the inoculum fermentation.According to the changes of flavor substances in the fermentation process,it could be preliminarily judged that the period of natural fermentation of sour bamboo shoots was about 30 days,and the period of inoculation fermentation was about 7 days.