Isolation And Identification Of Lactic Acid Bacteria In Tradional Yogurt Of Urumqi And Changji Region And Composite Optimization Of Fermentation Conditions

This research separated and identified the bacterias in the yogurt in Urumqi and Changji area.16SrDNA sequence analysis and phylogenetic analysis were made on some strains. The comparison curd time,acidity and sensory evaluation from fermented single bacteria are compared to choose the bestns.Based onsingle factor test, the fermentation conditions aretimized by response surface, the best fermentationconditions were determined. The fermentation function and the aromo of the compound strain were alsodetermined.1. In this study,20strains of lactic acid bacteria were isolated and purified from the Wu-changtraditional yogurt samples. According to phenotypic, physiological and biochemical properties strainsisolated were identified with the result of there were7strains of L. delbrueckii subsp. Lactis,3strains of L.casei,2strains of L. fermentum,3strains of L. lactis subsp. Lactis,2strains of Enterococcus faecalis,1strain of S. Salivarius. It can be seen that the region’s advantages bacteria were L. delbrueckii subsp. lactisand L. lactis subsp. Lactis. Four strains of Lactic acid bacteria︰CJ2, QT1, QT2, DB1were isolated fromthe samples.16S rDNA gene sequence analysis were made on the four strains, phylogenetic tree were alsoconstructed. The results showed that QT2and DB1were Lactobacillus delbrueckii subsp. Indicus, CJ2andQT1were Enterococcus faecalis.2. Determination curd、acidity and sensory evaluation by seven strains, screened two strains (CJ2,DB1) that curd time is short, good sensory quality for complex fermentation research.Univariate andresponse surface methodology to optimize the fermentation conditions of CJ2and DB1fermentation yogurt,and ultimately determine the optimum fermentation conditions︰inoculation ratio (CJ2︰DB1) was2︰3,inoculation amount was3%, the culture temperature was41°C, the fermentation time was4.5h, the sensoryevaluation was17.47.3. This study used SED-GC-MS assay aroma components from homemade yogurt and twocommercially available yogurts. And found Spiro[2.4]hepta-4,6-diene, Acetic acid, butyl ester,Ethylbenzene,1-Methylcyclooctanol,1,2-bis(1-methylethyl)-Benzene, Octanoic Acid, n-Decanoic acid,Dodecanoic acid, Hexadecanoic acid, ethyl ester,2-Mercaptobenzothiazole, Nonanoic acid,9-(o-propylphenyl) were all the main ingredient of yogurt aroma. The aroma component of the total peak areaand types of substances from homemade yogurt were higher than the commercially available yogurt.