Introduction: Listeria monocytogenes (LM) is a pathogen able to survive several environmental stresses. One strategy to prevent the growth of LM in meat products can be the addition of bacteriocin-producing lactic acid bacteria (LAB). One of the main problems concerning of the utilization of such LAB in these products is the low yield of bacteriocin production. It is known that immobilization of LAB can keep the microbial concentration and improve the production of lactic acid. However, little is known about its influence in situ in the bacteriocin production.
Purpose: This study aimed at evaluating the behavior of Listeria monocytogenes during the maturation of salami added of alginate-encapsulated Lactobacillus curvatus MBSa2, a bacteriocin-producer LAB isolated from salami.
Methods: MBSa2 strain was cultured in MRS broth, harvested by centrifugation and washed with peptone water (0.1%). The cells were encapsulated by adding 2% alginate and dripping the mixture in 100 mM CaCl2 solution. Salami was produced mixing pork meat, beef meat, fat, salt, Compact salami 160 (Kraki), starter culture T-SPX (Christian Hansen) and free or encapsulated L. curvatus MBSa2, and experimentally contaminated with LM (104-105 CFU/ml). Controls, added of a non-bacteriocin producing LAB (Lactobacillus sakei ATCC 15521) were also prepared. Meat mixture was fermented for four days (99%-97% RH, 20 °C) and ripened for 26 days (97%-75% RH, 18° - 15 °C). Counts of viable LAB and LM and determinations of the level of bacteriocin produced, pH and Aw were performed after 4, 10, 20 and 30 days.
Results: After of 30 days of maturation, counts of L. monocytogenes in salami with free L. curvatus MBSa2, encapsulated L. curvatus MBSa2, free L. sakei ATCC 15521 and with no added LAB were reduced 1.95, 2.47, 1.65 and 2.00 log CFU/g, respectively. No bacteriocin production was detected in all conditions studied, during 30 days of maturation. Initial pH values of the meat product were 5.97-5.92, and were reduced to 5.23-5.15 in 4 days, reaching 5.52-5.38 in 30 days. Initial Aw values were 0.98-0.97 and were reduced to 0.91-0.88 in 30 days.
Significance: These results indicate that reduction of counts of LM during the maturation of salami was similar in the tested products, regardless the presence of free or encapsulated bacteriocinogenic L. curvatus MBSa2.