Identification of lactic acid bacteria with anti-listeria activity. Characterization and application of a bacteriocinogenic strain in the control of Listeria monocytogenes in cheese.

The purpose of the research paper was firstly to identify bacteriocin-producing lactic acid bacteria characterizing strains with anti-listeria activity and, secondly, to characterize bacteriocin evaluating its in vitro efficiency as a natural preservative and, thirdly, to evaluate the anti-listeria effect of the bacteriocinogenic strain of Lactiplantibacillus plantarum in cheeses and produce an edible film with anti-listerial effect. Of 355 lactic acid bacteria strains tested, two were able to produce bacteriocin against Listeria monocytogenes and were identified as Lactiplantibacillus plantarum and Lactiplantibacillus pentosus. A bactericidal effect of strain QS494 (Lactiplantibacillus plantarum) was observed in the first 8 h, with a reduction of 1.7 log, using cell-free supernatant with Listeria monocytogenes, where viable cells were counted on listeria selective agar. Both strains showed good technological characteristics and were without production of virulence factors. Changes in the pH of the cell-free supernatant obtained from Lactiplantibacillus plantarum did not affect its antimicrobial activity, which remained stable after heat treatments for up to 15 min at 121°C. Inhibitory activity was also observed after 12 weeks of storage at -20°C. In the evaluation of the anti-listeria effect in cheeses, a 3 log reduction in the Listeria monocytogenes count was observed in 120 h in cheeses produced with bacteriocinogenic lactic acid bacteria, while in cheeses produced with non-bacteriocinogenic culture, we observed a 2 log increase in the count. Edible films produced with the addition of precipitate from the cell free supernatant showed an antimicrobial effect against Listeria monocytogenes. Thus, the two strains studied have technological and biosafety potential.

Pasteurized milk quality in Brazil: a cross-sectional study over five years.

This research communication delineates the quality of pasteurized cow milk sold in Brazil from 2015 to 2020. A cross-sectional study was performed gathering 1749 samples, which were evaluated for microbiological and physicochemical parameters, including Salmonella spp., total and thermotolerant coliforms, freezing point, alkaline phosphatase and lactoperoxidase. The proportion of compliant and non-compliant samples was compared through the years and jurisdiction of the inspection services. Interactions between the design and response variables were assessed by log-linear analysis. Overall, a considerable non-conformity rate (12%) was found for at least one microbiological or physicochemical parameter. Post-pasteurization contamination by coliforms was the major challenge for dairy industries. Notably, the non-compliance rate for freezing point increased during the SARS-CoV-2 pandemic. In addition, the ability to comply was linked to the type of inspection service. Thus, it is suggested that the SARS-CoV-2 pandemic is affecting the dairy industries in Brazil, and we strengthen the need for more studies monitoring the quality of milk over the years, which could assist industries and regulatory agencies to ensure the compliance of pasteurized milk.