Study On Anti Food-borne Microbial Mechanism Of Lactobacillus

Probiotics can produce secondary metabolites which are harmful to pathogenic and spoilage bacteria during growth and reproduction to compete with the growth space and nutrients till their death.It is called biological preservatives.Bio-corrosion technology has been applied to food fermentation industry ripely in a number of industrial countries.Yunnan province lies in the plateau regions of South-west of China.Because of the characteristic geographical environment and various of diet customs,Yunnan has rich resources of traditional fermented food.The microbiology diversity of fermented food vary from elevation gradient to geographic location.Lactic acid bacteria are dominant microorganism and play an important role in fermented food in some manufactory regions.Lactic acid bacteria produce a variety antimicrobial substances during fermented period.The antimicrobial substances interfere the normal growth of cell membrane,causing the deterioration of membrane potential and cell membrane penetration of nutrient loss,until pathogenic bacteria death.Meanwhile,a lot of researches were shown that the physiological health care functions of traditional fermented foods are closely relation to functional-microbial enzymes and the corresponding physiological active substances.Especially it is relative to the active substances produced by lactic acid bacteria.This study would study the correlation between antimicrobial activity and organic acid.The anti food-borne pathogens loci of fermented liquid derived from LAB was analyzed by scan electron microscope(SEM)and transmission electron microscope(TEM).The antimicrobial mechanism was studied preliminary.The food safety and nutritional function were revealed according to the results of beneficial bioactive substances ofour fermented yogurt and shelf life.The main research results are as follows:1.Fourty-four lactic acid bacteria strains were isolated from the traditional fermented douchi.These strains were identified as Lb.plantarum(eight strains),E.faedum(four strains),P.acidilactici(four strains),P.pentosaceus(four strains),W.paramesenteroides(four strains),Lb.fermentum(two strains),W.confusa(four strains),E.durans(three strains),W.cibaria(two strains),E.hirae(one strain),Lb.rhamnosus(one strain),L.lactis(four strains),Lb.brevis(two strains),Lb.casei(one strain)respectively.2.The antimicrobial activity of mentioned LAB strains were studied by agar well diffusion method and found that Lb.plantarum,P.acidilacticiham,W.paramesenteroides,Lb.casei had higher antimicrobial activity.3.It was found that the antimicrobial loci were different between E.coli 0157:H7 and S.aureus of ethyl acetate phase derived from Lb.casei AS02 strain culture supermatant analyzed by scanning electron microscopy and transmission electron microscopy.It was suggested that the difference of cell wall structure between gran-positive bacteria and gram-negative bacteria.4.To monitor the nine-week shelf life of the fermented yogurt,it was found that fermented yogurt can effectively inhibit the growth and reproduction of food-bome pathogens.Moreover,the inhibit effect against gram-negative bacteria was better than gram-positive bacteria.5.Comparison stydy on fermented yogurt and comuercial yogurt within shelf life period,Nine-week later,it was revealed that the number of surviving bacterium of fermented yogurt was 5x105 cfu/mL.