Study On The Quality Of Red Sour Soup Fermented By Separate And Mixed Material

Sour soup,as a typical representative of ethnic food in Guizhou Province,both nutrition and flavor"double-oriented"future food characteristics,but the traditional fermented red sour soup has a long period,unstable quality,which seriously restrict the development of red sour soup industry.Therefore,this thesis focuses on different processing methods of red sour soup as the research object,analyzed the microflora structure and physicochemical composition of tomato sour soup,chili sour soup and mixed sour soup during fermentation of split and mixed ingredients,and the dominant strains were explored,beneficial fermentation strains by morphological observation and fermentation characteristics tests were screened and identuficated,the liquid form of probiotic strain with natural tomato juice as carrier by optimization of culture medium and culture conditions was prepared.The acid-producing probiotic was inoculated with tomato sour soup and chili sour soup to fortify the fermentation,and then inoculated with aroma-producing probiotic to enhance the flavor,so as to build a"cascade fermentation model"of red sour soup and analyze the quality,in order to provide a scientific basis for the quality improvement of red sour soup.The main conclusions are as follows:（1）Sequencing analysis of amplicons（16S rDNA and ITS rDNA）showed that the microbial community diversity of red sour soup decreased as the fermentation time increased:Lentilactobacillus,Lactobacillus,Pichia and Issatchenikia predominate in tomato sour soup at mid-fermentation,chili sour soup and mixed sour soup dominated by Lactiplantibacillus,Levilactobacillus and Kazachstania,however,Lactobacillus,Lentilactobacillus and Kazachstania were all predominant in the late fermentation.The total acid content of the samples differed significantly（P<0.05）between the different fermentation periods,especially the total acid content of the mixed sour soup in late fermentation was significantly higher than that of the mid-fermentation period（30.47%increase on average）.The intensity of the sour signal increases with increasing fermentation time,the intensity of the bitter and salty signal decreases and the overall taste is harmonious,as tested by the electronic test.The evaluation of nutritional composition and antioxidant capacity showed that a total of 17 free amino acids were detected in the samples,and the content of sweet amino acids increased in the later stages of fermentation,the ABTS radical scavenging ability of the samples had the good quailty（all above 91.37±0.05%）.（2）The high-quality split-fermented tomato sour soup,chili sour soup and mixed sor soup were used as the source,and the isolation and identification of lactic acid bacteria and yeasts were focused on morphology,acid tolerance,bile salt tolerance,acid production,aroma production,antioxidant capacity,16S rDNA and 26S rDNA sequence analysis.One strain of lactic acid bacteria lt1-6 and lc2-1 were screened from each of tomato sour soup and chili sour soup,with acid production capacity of 7.41±0.02 g/kg and 7.92±0.01 g/kg,respectively,and one strain of aromatic yeast ym1-3（produces a strong fruity fragrance）was screened from the mixed sor soup.Using phylogenetic tree construction,three strains were identified as Lentilactobacillus buchneri（the abbreviation is L.buchneri）,Pediococcus ethanolidurans（the abbreviation is P.ethanolidurans）and Kazachstania bulderi（the abbreviation is K.bulderi）respectively.Verified by cascade fermentation system（1:1 combination of tomato sour soup and chili sour soup after 96 h of fermentation with L.buchneri and P.ethanolidurans respectively and then inoculated with K.bulderi for 96 h）.The strain grew well during the fermentation of red sour soup（（4.925±0.020）×10⁷ CFU/m L for L.buchneri in tomato sour soup,（5.900±0.021）×10⁷ CFU/m L for P.ethanolidurans in chili sour soup,（0.150±0.030）×10⁷ CFU/m L for K.bulderi in mixed sor soup）,and high acid produced by fermentation（p H values all below 3.51±0.02）.（3）Optimized by single-factor and orthogonal tests,the optimum medium and culture conditions for lt1-6 were sucrose 20 g/L,soybean peptide 20 g/L,tomato juice190 g/L,inoculum 1%and temperature 37°C,respectively.The optimum medium and culture conditions for lc2-1 were sucrose 30 g/L,soybean peptide 20 g/L,tomato juice120 g/L,inoculum 3%and temperature 30°C,respectively.The optimum medium and culture conditions for ym1-3 were sucrose 20 g/L,soybean peptone 30 g/L,tomato juice35 g/L,inoculum 5%and temperature 30°C,respectively.The liquid inoculum was prepared according to the above optimized conditions,and the bacterial density(OD_600nm)in the log phase of lt1-6,lc2-1 and ym1-3 were 2.455,0.427 and 2.825,respectively,which higher than the density of the bacterium before optimization.The liquid inoculum with tomato juice as the carrier will be used in the red sour soup cascade fortified fermentation system.（4）By comparing four fermentation modes（split fortified fermentation,split natural fermentation,mixed fortified fermentation and mixed natural fermentation）,quality evaluation of their samples on days 1,6 and 10 showed that,fortified fermentation can accelerate the p H drop of red sour soup,total lactic acid bacteria,total acid and amino acid nitrogen content are higher than natural fermented red sour soup.The fortified fermentation could effectively control the content of nitrite during the fermentation process,and the sour signal is stronger,fresher and lighter in saltiness.The fortified fermentation resulted in a rapid increase of lactic acid content in the red sour soup,with a total organic acid of 26.776±8.351 g/kg for MQ10.Morevoer,the results of GC-IMS analysis showed that there were 96 volatile flavor substances,mainly including terpenes,aldehydes,esters and alcohols,but there were significant differences in the composition of volatile substances among the samples,the fingerprinting further showed that the content of esters（such as ethyl butanoate,butyl acetate et al.）and alcohols（such as 2-ethyl-1-hexanol,1-hexanol et al.）was higher in the fortified fermented red sour soup,among them,alcohols such as 1-hexanol（fruit aroma）are higher in fortified split-fermented red sour soup than in mixed fortified fermentation,and esters such as isobutyl acetate（ripe fruit aroma）are higher in mixed fortified fermentation.Furthermore,percentage of total cis-lycopene in fortified fermented red sour soup（9.454±0.337%in FMQ10,9.540±0.559%in MQ10）higher than natural fermentation（3.180±0.676%in FMZ10,5.217±0.686%in MZ10）.