The Isolation, Identification And Analysis Of Antimicrobial Component Of Lactic Acid Bacteria Inhibiting Fungi In Pickles

Because of high moisture content, pickles could be easily conta min ated by various fungi during production,processing and storage. Some fungi may also produce mycotoxin and cause food poisoning. In recent years, a number of studies on the inhibition of lactic acid bacteria on spoilage and pathogenic bacteria have caused great concern. Currently, the inhibitory effect of various lactic acid bacteria separated from fermented food has been confirmed, however,whether lactic acid bacteria exist in pickles,the inhibitory effects on mold and the analysis of antibacterial substances was rarely reported.Co mmercial pickles were available for this study,from which lactic acid bacteria and mold were separated. Screening the lactic acid bacteria which could inhibit the growth of moldfor molecular biological identification and primary analysis of the antimicrobial substances; Detecting the inhibitory activity and antifungi substances of selected lactic acid bacteria on pathogenic bacteria growth which are co mmon in food; Inoculating a strain of lactic acid bacteria with the highest inhibitory activity in pickles raw materials to evaluate the influence of lactic acid bacteria on pickles’ quality and shelf life through the sensory test and microbial indicators. Through the study we can make the following conclusions:L511, L520, L544 has good inhibitory effect on four toxin-producing fungi from pickles and two strains of toxigenic mold. After the analysis of antimicrobial active ingredients, we found that the substances of inhibiting effective in the broth concentrate of L511 and L520 are polypeptides(or proteins) and organic acids, in other words, peptides(proteins) only have antibacterial activity in acidic condition, and the active substances have high thermal stability. Substances with inhibiting effect in the broth concentrate of L544 are polypeptides(or proteins) and organic acids, while acidity of environment has no effect on it’s inhibition activity to fungal,and the thermal stability is high. These fungi were then identified via 18 s rDNA sequence blasting and were identified as F1: Cladosporium, F2: Penicillium, F3: Aspergillus, F4: Fusarium.Fermentation of three lactic acid bacteria showed different levels of antibacterial activity to four pathogens. Through the analysis of antimicrobial active ingredients, antibacterial activity of Lactic acid fermentation broth against pathogenic bacteria were highly affected by pH in the fermentation broth. The main antibacterial substances against pathogens of L511 and L520 are organic acids, or peptide(or protein) can only exert its inhibitory activity under acidic conditions. Substances with inhibiting effect in the broth concentrate of L544 are polypeptides(or proteins) and organic substances, and the exert of inhibitory activity is affected by genus of test bacteria.By method of Sodium benzoate, L544, or combination of the two can effectively extends the shelf life of pickles. However, the combination of sodium benzoate and L544 as a composite preservative has min imum effect on the quality of pickles. When adding the preservative compound into pickle samples, lactic acid bacteria were in a do min ant position in the 90 d period. Sodium benzoate and L544 have good effect in inhibiting the growth of spoilage bacteria, fungi, yeast, and have good synergy and a stronger inhibitory effect when both used. Limited use of sodium benzoate have no significant impact on the growth of L544. This study has significance to extent the shelf life of pickles in the future.