Food and Beverages

Introduction: Listeria monocytogenes is a great concern in the food industry. Bacteriocins, produced by Lactic Acid Bacteria (LAB) are of great importance in order to face this concern. The reason for that is because some bacteriocins have demonstrated antimicrobial activity against L. monocytogenes and do not alter the organoleptic characteristics of the products. MRS broth can fulfil fastidious growth requirements of most LAB, so it is used for the growth of Lactic Acid Bacteria and for bacteriocin production. It is known that pH can have some effects over the production of bacteriocins. So, the objective of this study was to investigate how the pH value could influence the growth of an autochthonous strain of Lactobacillus and the production of bacteriocin active against L. monocytogenes. Methodology: From previous studies with different LAB, isolated from traditional meat products, an autochthonous Lactobacillus strain was selected since it demonstrated antimicrobial activity against L. monocytogenes and do not alter the organoleptic characteristics of the tested products. Bacteriocins were tested against five strains of Listeria monocytogenes. The selected Lactobacillus strain was grown in MRS broth for 21 h at 37°C in a batch reactor. Two different batchs were prepared. In one pH was controlled over time (pH=6.5) and in the other one LAB growth and bacteriocin production were performed under uncontrolled pH.  Results & Conclusions: Higher bacteriocin activity was observed when LAB were grown under controlled pH. Maximum

antimicrobial activity was about 12800 Au/mL for every Listeria monocytogenes tested, after 18 hours of LAB growth when the pH of the medium was controlled. This antimicrobial activity could be maintained, even after 20 hours of LAB growth.