Selection Of Producing Lactobacillin Strains Of Lactic Acid Bacteria And Its Applications In Meat Products And Pepper Fermentation

Lactic acid bacteria (LAB) are a group of bacteria that can fermentcarbohydrate and produce a great number of lactic acid. They can produce organic acid,bacteriocin, hydrogen peroxide and diacetyl in fermentation. Studies have shown lacticacid bacteria not only have a lot of special physiological functions to human body, theyand their metabolites can inhibit the growth of Bacillus cereus, clostridium botulinum,clostridium perfringens, Listeria monocytogenes and Staphylococcus aureus. At thesame time, bacteriocin as one pure natural nonpoisonous preservative can replacechemical preservative partly. So the method that ferments fruits and vegetables withlactic acid bacteria not only can improve the nutrition and flavor of the products butalso can preserve and reduce the content of nitrate. With the development of technology,lactic acid bacteria and their metabolites have received the extensive attention ofvarious countries because of their uses and potential applications in many fields. Soselecting antibacterial LAB has important significance.Three strains with stronger antibacterial function were isolated from fermentedpepper and pickles. Their fermented performance, physical and chemical characters ofmetabolites, preservative function and the application in fermenting pepper werestudied in this study. The following was the main results:(1) The identification and antibacterial function of the three strains were studied.Three strains were identified to be LAB and called Lact.1(L.Lactis), Lact.2(L.brevis)and Lact.3(L.plantarum). Their metabolites had obvious inhibition to Staphylococcusaureus and Listeria monocytogenes. The antibacterial diameter of the three strains toListeria monocytogenes was 12.8mm, 10.1 mm and 10.8 mm, and to Staphylococcusaureus was 15.6mm, 12.2mm and 13.6 mm respectively. Their metabolites also hadsome inhibition to Escherichia coli, Bacillus cereus and Clostridium perfringens.(2) The fermented performance of the three strains was studied in this paper. Thebest growth temperature of the three strains was between 30℃-35℃. The speed of acidproducing was very fast. The pH value of fermented liquid of Lact.1 was to be 3.9 from 6.5 in 12h, and the pH value of fermented liquid of Lact.2 and Lact.3 was to be 4.2from 6.5 in 12h.The last pH value of fermented liquid of three strains was to be 3.5 orso; The salt content had obvious inhibition on the growth of the three strains, but thethree strains can grow in MRS with 8% salt or so, and inhibited when salt concentrationwas more then 10%.(3) The three kinds of metabolites were proved to be bacteriocin afterelectrophoresis and study of physical and chemical characters. The three kinds ofmetabolites were called Bact.1, Bact.2 and Bact.3 respectively. The molecular weightwas 5.7kda, 6.0kda and 3.4kda or so respectively.(4) The three kinds of metabolites had good heat stability when heated at 80℃Heated at 121℃for 15min, the antibacterial diameter of the three metabolitesreduced by 19% and 9% and 20% respectively. But when heated at 121℃for 15min,the antibacterial diameter of the three metabolites reduced by 45% and 10% and 36%respectively which could prove that Bact.2 was a kind of heat-stable protain. Becauseof their heat-stable characters, they had good potential applications. Bact. 1 and Bact.3had the highest antibacterial activity at pH6 or so, and showed high activity at pH4-7;Bact.2 had the highest antibacterial activity at pH5 or so, and showed high activity atpH2-7.(5) Through studying preservative function of three kinds of bacteriocin in meat,the result was that the order of magnitude of total microorganism in the group with oneof the three kinds of bacteriocin was 2-3 orders of magnitude lower than those of thegroup without bacteriocin. Bact.1 and Bact.2 and Bact.3 can inhibit the growth ofStaphylococcus aureus. The inhibition effect had relation with the concentration ofStaphylococcus aureus.(6) The best parameter of fermented pepper was that the inoculating amount ofLact.1, Lact.2 and Lact.3 was 1%, 1% and 0.5% respectively and adding amount of saltwas 10%. Through comparing the composition and content of the flavor materials,there was no obvious difference between naturally and inoculated fermented pepper.But the production cycle of inoculated fermented pepper was 5d shorter then that ofnaturally. (7) Lact.1, Lact.2 and Lact.3 can make the nitrate concentration of MRS from125.00mg/l to 20mg/l, 38.32mg/l and 35.26mg/l respectively in 72h. The ability was3-4 times of other two strains preserved in lab. The maximum nitrate content innaturally and inoculated fermented pepper was 25.06μg/g and 1.56μg/g respectivelyduring the fermentation. The nitrate content of naturally fermented product was 3.1μg/g;but the nitrate content of inoculated fermented product was only 0.1μg/g.