Study On The Characteristics Of Lactic Acid Bacteria During The Fermentation Process Of Northwestern Shanxi Sour Porridge

Lactic acid bacteria are very important in organism and environment.Lactic acid bacteria can not only improve the nutritional value of food,give food good organization and flavor,extend the shelf life,but also have a variety of health care function to human body.Meanwhile,lactic acid bacteria are of great significance in the development of lactic acid bacteria as functional foods.This paper studied the potential probiotics of 20 strains of lactic acid bacteria isolated from northwestern Shanxi traditional cereals fermented food—sour porridge.Five strains of lactic acid bacteria were screened and identified,and their antimicrobial activities and antibiotic resistance were analyzed.The 20 strains of lactic acid bacteria were studied in their tolerance to acid and bile salt,hydrophobicity,in vitro cholesterol-reducing and antioxidant activity.The results showed that the survival rate of 14 strains of lactic acid bacteria,which were cultured in MRS liquid medium of pH3.0 for2 h,was more than 50%.The survival rate of 6 strains was more than 100%.The strain M-1,M-5,M-8,M-9,M-10 and M-13 were highly tolerant to bile salt.The strain M-19 exhibited good hydrophobicity.The cholesterol degradation rate of 12 strains of lactic acid bacteria was more than 50%.The strain M-8 had a better tolerance to hydrogen peroxide and higher scavenging activities on hydroxyl radical and DPPH free radical.In conclusion,5 strains numbered M-1,M-5,M-8,M-10 and M-15 showed good probiotic characteristics,and were identified as Lactobacillus brevis by 16 S rDNA sequence analysis.The antimicrobial activities in vitro of fermentation supernatant from 5strains were studied.The results showed that they could all obviously inhibit the growth of Staphylococcus aureus,and the antimicrobial activity of strain M-1 was the strongest.The fermentation supernatant of 5 strains had strong antimicrobial activities in pH 2.0~5.0.When the pH reached neutral,the other strains still had good antibacterial effect except for strains M-5 and M-8.Moreover,the antimicrobial activities of 5 strains were not changed apparently after treated with the catalase,but were distinctly reduced after treatment with the pepsin,trypsin and protease K.And the strains M-5 and M-8 had no antimicrobial activities after treatment with different proteases.The inhibition zone diameter of fermentation supernatant from 5 strains were slightly decreased after heat treated at 60?,80? and 100 ?.But their antimicrobial activities had no evident decline.To sum up,fermentation supernatant of 5 strains still had good antibacterial effect after eliminating the interference of organic acid and hydrogen peroxide.It showed that there are other antimicrobial active substances,which were sensitive to protease,preliminarily classified as bacteriocin that has good thermal stability.The antibiotic resistance of 5 strains was analyzed.The results showed that they were resistant to penicillin,cefotaxime,tetracycline and streptomycin,and sensitive to ampicillin and erythromycin.The strains M-1and M-10 were sensitive to chloramphenicol,while the strains M-5,M-8 and M-15 showed moderate sensitivity to chloramphenicol.