PURIFICATION AND IDENTIFICATION OF ANTIMICROBIAL SUBSTANCES PRODUCED BY 2 LACTOBACILLUS-CASEI STRAINS

The antimicrobial substances produced by Lactobacillus casei ssp. case i LC-10 (LCC) and L. casei ssp. pseudoplantarum LB1931 (LCP) were stud ied by ethanol precipitation, gel filtration, anion exchange, reversed -phase high-performance liquid chromatography, nuclear magnetic resona nce and mass spectroscopy. The results showed that in addition to lact ic acid predominantly produced in the MRS broth culture, 2-pyrrolidone -5-carboxylic (PCA), also known as pyroglutamic acid, was formed and i t was separated and found to contribute the antimicrobial activity of LCC and LCP. The purified PCA shown inhibition toward several spoilage bacteria, such as Bacillus subtilis 1205, Bacillus subtilis MCM-1, En terobacter cloacae 1575 and Pseudomonas putida 1560-2. Since no antimi crobial activity was detected in the precipitates from the step of eth anol precipitation, it seemed that bacteriocins were not produced by L CC and LCP. The technique of anion-exchange chromatography developed i n this study was essential for effective separation of lactic acid fro m other antimicrobials.