Impact of Nisin and Nisin-Producing Lactococcus lactis ssp. lactis on Clostridium tyrobutyricum and Bacterial Ecosystem of Cheese Matrices

Clostridium tyrobutyricum spores survive milk pasteurization and cause late blowing of cheeses and significant economic loss. The effectiveness of nisin-producing Lactococcus lactis ssp. lactis 32 as a protective strain for control the C. tyrobutyricum growth in Cheddar cheese slurry was compared to that of encapsulated nisin-A. The encapsulated nisin was more effective, with 1.0 log10 reductions of viable spores after one week at 30 °C and 4 °C. Spores were not detected for three weeks at 4 °C in cheese slurry made with 1.3% salt, or during week 2 with 2% salt. Gas production was observed after one week at 30 °C only in the control slurry made with 1.3% salt. In slurry made with the protective strain, the reduction in C. tyrobutyricum count was 0.6 log10 in the second week at 4 °C with both salt concentration. At 4 °C, nisin production started in week 2 and reached 97 µg/g after four weeks. Metabarcoding analysis targeting the sequencing of 16S rRNA revealed that the genus Lactococcus dominated for four weeks at 4 °C. In cheese slurry made with 2% salt, the relative abundance of the genus Clostridium decreased significantly in the presence of nisin or the protective strain. The results indicated that both strategies are able to control the growth of Clostridium development in Cheddar cheese slurries.

Effects of the Essential Oil from Origanum vulgare L. on Survival of Pathogenic Bacteria and Starter Lactic Acid Bacteria in Semihard Cheese Broth and Slurry

ABSTRACT This study assessed the inhibitory effects of the essential oil from Origanum vulgare L. (OVEO) on Staphylococcus aureus, Listeria monocytogenes, and a mesophilic starter coculture composed of lactic acid bacteria (Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris) in Brazilian coalho cheese systems. The MIC of OVEO was 2.5 μl/ml against both S. aureus and L. monocytogenes and 0.6 μl/ml against the tested starter coculture. In cheese broth containing OVEO at 0.6 μl/ml, no decrease in viable cell counts (VCC) of both pathogenic bacteria was observed, whereas the initial VCC of the starter coculture decreased approximately 1.0 log CFU/ml after 24 h of exposure at 10°C. OVEO at 1.25 and 2.5 μl/ml caused reductions of up to 2.0 and 2.5 log CFU/ml in S. aureus and L. monocytogenes ,respectively, after 24 h of exposure in cheese broth. At these same concentrations, OVEO caused a greater decrease of initial VCC of the starter coculture following 4 h of exposure. Higher concentrations of OVEO were required to decrease the VCC of all target bacteria in semisolid coalho cheese slurry compared with cheese broth. The VCC of Lactococcus spp. in coalho cheese slurry containing OVEO were always lower than those of pathogenic bacteria under the same conditions. These results suggest that the concentrations of OVEO used to control pathogenic bacteria in semihard cheese should be carefully evaluated because of its inhibitory effects on the growth of starter lactic acid cultures used during the production of the product.

Isolation of anticlostridially active lactobacilli from semi-hard cheese

The group of 7 strains of facultatively heterofermentative lactobacilli (FHL) of the non starter lactic acid bacteria (NSLAB) isolated from semi-hard cheeses using a well agar diffusion assay possessed a different level of inhibition activity against 16 different strains of <I>Clostridium</I> sp. belonging to the species <I>Cl. butyricum, Cl. tyrobutyricum, Cl. beijerinckii</I>, and <I>Cl. sporogenes</I>. Two selected strains with the production of partially indentified anticlostridially active inhibitory substances, <I>Lb. paracasei</I> ST68 (producing hydrogen peroxide) and <I>Lb. paracasei</I> 171R2 (producing bacteriocin and hydrogen peroxide), were tested for the inhibition activity against gas producing <I>Cl. butyricum</I> 10702 and <I>Cl. tyrobutyricum</I> 184 in cheese slurry. The effects of both strains were different in reducing the numbers of gas producing <I>Cl. butyricum</I> 10702 by > 3 log cycles and <I>Cl. tyrobutyricum</I> 184 by > 1 log cycles in cheese slurry during the tested storage periods of 24 days at 13°C. The <I>Cl. tyrobutyricum</I> strains isolated from spoiled cheese were identified by species-specific PCR for <I>Cl. tyrobutyricum. </I>