Screening,identification And Characterization Of Acid-tolerant Lactic Acid Bacteria In Low-salt Pickles

As a traditional fermented food in our country,kimchi is widely favored by consumers for its unique flavor and rich nutritional value.At the same time,lactic acid bacteria,as a very important physiological flora in the intestinal tract,balance the microecological structure of the human body and are closely related to health.In this experiment,12 low-salt kimchi samples from 14 different regions,selected for the isolation,purification,morphology,physiological and biochemical identification and 16S rDNA molecular identification of lactic acid bacteria.5 lactic acid bacteria were identified and their probiotic properties were studied.It not only caters to the low-salt diet,but also provides theoretical support for future research on the compounding of multiple strains.The specific research results are as follows:(1)The salt content of 14 kinds of kimchi samples were between 0.87-9.48%,the salt content of 2 kinds of kimchi more than 6%,which belongs to medium-salt kimchi,and the rest were low-salt kimchi.The pH of the kimchi samples were between 2.80-5.31,and the pH of pickled red pepper was the lowest,and the radish had the highest pH.(2)126 strains were isolated from 12 kinds of kimchi samples,and 5 strains were obtained through the acid tolerance screening experiment.Observed by morphology,5 strains were milky white with regular edges and smooth surface;physiological and biochemical identification results showed that all were Gram-positive,blue-violet,and catalase negative,and no bubbles were generated;through 16S rDNA molecular identification and homologous sequence comparison analysis,the strains were numbered and named,the 5 strains were Leuconostoc mesenteroides J2,Lactobacillus paracasei N6,Lactobacillus paraplantarum F8,Weissella cibaria M1,Weissella cibaria M12.(3)The results of 5 strains growth curve measurement showed that the growth rate of strain M12 was the highest,and the OD600 value reached 2.42 at 24 h,and the growth curves were sorted as:M12>M1>N6>F8>J2.Comparing the acid tolerance of 5 strains,the strain N6 has the strongest acid tolerance,and the acid tolerance rank is N6>M1>M12>F8>J2;comparing the acid-generating activity of the five strains,the strain N6 has the highest acid-generating activity,reaching 5.05 U,and there were not much differences in acid-generating activity between the strains.(4)In the artificial simulated gastric and intestinal juice experiments,strain N6 had the best tolerance in extreme environments,and the comprehensive tolerance of 5 strains was ranked as N6>M1>M12>F8>J2.After 8 hours of cultivation in 0.3%bile salt medium,the survival rates of strains N6,M12,M1,J2,and F8 were 41.16%,31.18%,30.68,23.10%,and 17.83%.(5)In the hydrophobicity experiment,4 strains have high hydrophobicity,among which strain N6 reaches 78.72%,but strain J2 was a moderately hydrophobic strain,and the hydrophobicity was only 42.81%;in the self-agglutination experiment,strain N6 reached 76.51%after 24 hours of culture,and the probiotic characteristics of strains M12 and M1 were also good.(6)Comprehensively compare the growth curves,acid-generating activity,acid tolerance,and in vitro probiotic characteristics of the five strains,the comprehensive ranking result was N6>M12>M1>F8>J2.