Control de Listeria monocytogenes en embutidos curadomadurados y quesos madurados tradicionales mediante cultivos protectores e hidrolizados proteicos

Abstract

In this Doctoral Thesis, lactic acid bacteria have been isolated from traditional dry-cured fermented sausages and ripened cheeses and have been selected based on their anti-L. monocytogenes for its possible use as a biocontrol strategy with protein hydrolysates. The 371 LAB isolates obtained were successively evaluated for their anti-L. monocytogenes and by the presence of genes encoding bacteriocins. This methodology made it possible to select 5 strains of each product that cause significant reductions in L. monocytogenes. Three of these strains confirmed their activity during the industrial ripening of dry-cured fermented sausages and “Torta del Casar” cheese type, causing reductions in this pathogen of between 2 and 5 log CFU/g. However, whey protein hydrolyzate was ineffective and was discarded. Analysis of PFGE with restriction enzymes SgsI and NotI allows differentiation of selected LABs at the strain level. The developed qPCR method detects increases in the expression of virulence genes under conditions of acidity in sausages and cheeses. Lactilactobacillus sakei 205 and Lacticaseibacillus casei 116 (registered as a patent) were selected as active strains, producers of bacteriocins, innocuous, without resistance to antibiotics and that do not negatively modify the sensory characteristics of ripened foods.