Study On Isolation Identification And Fermentation Characteristics Of Lactic Acid Bacteria In Kefir

Kefir is a traditional fermented dairy product with rich in lactic acid bacteria(LAB),and the conservation and utilization of LAB strains in it is of great significance.In this study,LAB were isolated and identified from five Kefir samples from different regions of China by pure culture method,and two LAB strains with good fermentation characteristics and potential probiotic properties were selected and fermented with the basic fermenting agent PYS-010 to prepare fermented milk.The main results were as follows:(1)Lactic acid bacteria were isolated and purified from five Kefir samples collected from Inner Mongolia,Shandong,Heilongjiang and Jiangsu,and identified by 16 S r DNA sequence homology comparison and phylogenetic relationships.80 strains of LAB were obtained belonging to six genera and nine species.Six genera were Lactobacillus(Lb.)Lacticaseibacillus(L.),Leuconostoc(Leu.),Lactiplantibacillus(La.),Enterococcus(En.)and Lactococcus(Lac.).Lactobacillus was the dominant genus,Lb.kefir was the dominant species.(2)Eighty purified LAB strains were subjected to single bacteria fermentation,and two LAB strains with good fermentation characteristics and potential probiotic properties,L.paracasei A35 and,Lac.lactis E24 were selected through experiments on curdling characteristics,acid production,viscosity production,water holding capacity and sensory score.(3)The fermented milk was prepared by combining L.paracasei A35 and Lac.lactis E24 with the basic fermenting agent PYS-010 at different ratios.The fermentation time was short,the acidity at the end of fermentation was moderate,the sensory evaluation score was 86,and 68 volatile flavour substances such as esters,aldehydes and ketones were detected by SPME-GC-MS,and the number of viable bacteria and the fermentation characteristics were stable during storage.In conclusion,the fermentation characteristics of the two LAB strains(L.paracasei A35 and Lac.lactis E24)isolated and screened from Kefir were good,and their application in combination with commercial fermenters in a certain proportion could improve the fermentation characteristics,storage stability and sensory evaluation of the fermented milk.This study also provides a basis for the development and use of functional dairy products.