The Production Of Phenyllactic Acid By Probiotics And Atimicrobial Effection Against Escherichia Coli

Phenyllactic acid(PLA)is a small molecule bactericidal substance with properties of safety,non-toxic,good stability and easy to spread in the food system.PLA also can inhibit and kill a variety of microorganisms such as pathogenic bacteria and putrefying bacteria.This paper was designed to screen out a maximum PLA production capacity of safety strains from natural fermented food,which also research synthesis pathway of PLA and preliminary study on the antibacterial properties of PLA to E.coil.We detected the PLA content in the homemade and finished pickle juice by using HPLC,samples contained PLA,but there were individual differences,the highest pickle samples K was 49 mg/mL.We screened out 34 strains of lactic acid bacteria from the homemade pickles,including 29 strains have the ability to produce PLA.Strain K1 fermented in the MRS medium at 37? of 24 h,which screened out from high content of pickle samples K,PLA yield was 86 mg/mL.Strain K1 was identified as Lactobacillus plantarum by morphological analysis and 16S rDNA sequence analysis,which named Lactobacillus plantarum CNQ7.We got the Genbank asscession number KJ003858 by submitting the nucleotide sequences.L.plantarum CNQ7 was used in fermented pickles,the highest yield of PLA in fermented carob for 7 days was 35 mg/L,the highest yield of fermented cabbage was 18 mg/L.L.plantarum CNQ7 was used to ferment mustard,we compared with PLA yield of adding phenylalanine group and no adding group and found that the former highest yield.was 23 mg/L,the latter was 12 mg/L.This shows that adding a certain amount of phenylalanine to promote the synthesis of PLA.The ability of inhibition to E.coli 44752 about the three different configurations of PLA was to be compared using the agar diffusion method,the results showed that three of antibacterial ability of E.coli 44752 was equivalent.MIC and MBC to the E.coli 44752 of the three PLA were to be measured using the microdilution method,MIC was 1.25 mg/mL,MBC was 2.5 mg/mL.The MIC of lactic acid,acetic acid and sodium benzoate was 1.25 mg/mL,0.5 mg/mL,10.5 mg/mL respectively.The antibacterial action of three kinds of food additives in combination with PLA was used checkerboard test.The interaction between PLA and lactic acid resulted in FIC index 0.18,the interaction between PLA and acetic acid resulted in FIC index 0.5,the interaction between PLA and sodium benzoate resulted in FIC index 0.12.The FIC index was lower than 0.5 which represents a synergistic interaction between PLA and the three food additives.The time kill curves were to be drawed about PLA three food additives.The bactericidal kinetic curves of E.coli 44752 composed with PLA was depicted which lays the foundation for the follow-up study of bacteriostatic mechanism of PLA.We conclude the membrane permeability would be changed by detection the leak amount of UV-absorbing substances at 260 nm.