Study On The Quality Characteristics And Microbial Community Of Traditional Bacterial Douchi In Southwest China

Bacterial douchi is a common soybean product fermented from Bacillus,Micrococcus and Lactobacillus species in Southwest of China.It has the characteristics of rich nutrition and unique flavor.It is mainly distributed in Sichuan,Hubei,Guizhou and Yunnan and other places of China.At present,the production method of bacterial douchi is still based on small workshop-style traditional natural fermentation.Due to the difference of geographical conditions and production conditions,the product quality will be different.In view of this,this article takes the bacterial douchi products produced in Chongqing,Guizhou,and Yunnan as the research object,mainly starting from its basic nutritional quality,physical and chemical characteristics,flavor quality and microbiota,to study the quality characteristics and microbiota of bacterial douchi products in the southwestern region to further understand the relationship between bacterial douchi flavor quality and microorganisms,provide basic research data for the safe consumption of commercially available bacterial douchi,and provide support for the industrial production of bacterial douchi.The main research contents and results are as follows:(1)The basic quality-related indicators of bacterial douchi in different regions were detected and analyzed.The results showed that the moisture content of dry douchi was 16.42%-37.24%,and the moisture content of wet douchi was 41.47%-67.29%.Basic nutrient analysis shows that the fat and protein content of douchi in Guizhou is higher than that in Chongqing and Yunnan,and the ash content varies significantly from region to region.Functional component analysis showed that the content of isoflavones and soy saponin of douchi in Guizhou area was higher than that in Yunnan and Chongqing.The content of isoflavones of douchi in Chongqing was generally lower,but the polysaccharide content of douchi in Chongqing was generally higher.The analysis of color and texture characteristics shows that the color of douchi in Yunnan is generally darker than that of douchi in Chongqing and Guizhou;the hardness of dried douchi is significantly higher than that of wet douchi,and the hardness is positively correlated with the chewiness;douchi in Guizhou has the highest elasticity,followed by Douchi in Chongqing area and Yunnan area have the lowest elasticity,which is positively correlated with cohesion.Analysis of physical and chemical properties and hygienic indicators shows that the p H value of douchi from different sources is significantly different,and the nitrite content meets the safety standards stipulated in GB2760-2014(?30mg/kg),and the TVB-N content is far lower in the SB/T 10294-2012 first grade standard limit of cured pork(?20 mg/100 g),the POV value is at a low level(?1.94 meq/kg),and the total number of colonies in Guizhou is higher than that in Chongqing and Yunnan..Antioxidant activity and protein in vitro digestion analysis showed that the degree of browning of douchi in Yunnan was lower than that in Chongqing and Guizhou.The antioxidant capacity of douchi produced in Yunnan was generally weaker than that of douchi in Guizhou and Chongqing.The protein digestibility of douchi in Yunnan was higher than that in Guizhou and Chongqing produced douchi;correlation analysis shows that polyphenols are related to the antioxidant activity of douchi,but the antioxidant activity of douchi is affected by other factors.According to the comprehensive analysis,the douchi produced in Guizhou is better.(2)The measurement and analysis of the relevant indicators of the flavor quality of the bacterial types in different regions showed that: from the perspective of regional factors,the content of soluble protein,free amino acids and non-protein nitrogen of douchi in Yunnan is higher than that in Guizhou and Chongqing,and the content of peptide and amino acid nitrogen of douchi in Guizhou is better than that in Chongqing and Yunnan;douchi in Chongqing has the highest free fatty acid content;from the perspective of the dry and wet state of douchi,the content of all protein-related indexes of wet douchi is higher than that of dry douchi.Dry douchi is in the content of free fatty acid and total acid and sodium chloride is higher than that of wet douchi,while the content of reducing sugar and total sugar are lower than that of wet douchi.Analysis of volatile components showed that the main volatile substances in 21 types of bacterial douchi were linalyl acetate,terpineol acetate,ethyl palmitate,Dlimonene,anisene,gingerene,phenethyl alcohol,linalool,and geraniol,Maltol,2-Undecone,2,3,5-Trimethylpyrazine,Tetramethylpyrazine,Isovaleric Acid,2-Methylbutyric Acid.Sensory evaluation showed that water douchi and wet douchi were highly accepted by consumers.Among the top 8samples,7 samples were water douchi or wet douchi,and only No.9 was dry douchi;the sensory evaluation of dry douchi ranked lower.This is related to the fact that the bacterial douchi will produce special flavors during the air-drying process,which makes dried douchi become a favorite fermented food.Correlation analysis showed that there was no correlation between douchi taste quality index and sensory score(P>0.05).Among volatile flavor substances,phenylethyl alcohol with rose aroma(P<0.05)and bergamot-like linalyl acetate(P<0.05)0.01)is positively correlated with sensory scores,indicating that food acceptance is affected by other factors,and volatile components in douchi affect sensory acceptance.Principal component analysis showed that douchi from Guizhou ranks first,and the top four are douchi samples from Guizhou 1,2,8,and 9.Considering the place of origin and dryness and wetness,samples 1,2,and 9 are selected for subsequent microbiome research.(3)The microbial diversity analysis and the screening and identification of dominant strains on the douchi samples of Guizhou area 1,2 and 9 showed that the microbial diversity test results showed that in the douchi samples of Guizhou No.1 douchi had the widest distribution and the shortest distribution Bacillus followed.In addition,the distribution of Bacillus coagulans,Staphylococcus squirrel,Bacillus stipitis,Bacillus thermophilus,and Bacillus spp.gradually decreased;in the No.9douchi sample,Bacillus thermophagophagous had the widest distribution.Bacillus thermophilus followed;Bacillus coagulans in the No.2 douchi sample was the most widely distributed,followed by Bacillus thermophagocyticum.Compared with samples No.1 and No.9,glutamate rods were also detected in No.2 sample.Bacillus.Preliminary identification results of physiological and biochemical tests showed that bacteria 1-3,2-1,and 9-3 are Bacillus subtilis,bacteria 2-2 and 9-1 are Bacillus amyloliquefaciens,and bacteria 1-1 are Bacillus coagulans,No.1-2 is Bacillus sphaericus,No.2-3 is Bacillus brevis,and No.9-2 is Pediococcus,similar to the 16 S r RNA sequencing results.Correlation analysis of bacterial communities,volatile flavor substances,and flavor quality related indicators shows that the distribution of bacterial communities detected in the three types of douchi samples in Guizhou area and the taste quality of douchi,alcohols,esters,carboxylic acids,olefins,etc.The formation of volatile flavor substances is closely related.