IMPROVEMENT OF FOOD SAFETY AND MICROBIAL INTERACTIONS

In these studies, different approaches for the conservation of meat and fish products were deepened. The application of bioprotective cultures and the addition of organic salts were investigated, following the current trends of demanding mild technologies for food, in order to contrast the pathogenic and spoilage microorganisms without significant modifications of the sensorial quality of the products. In the first study, the anti-listerial activity of L. sakei strains, isolated from salmon scraps, was observed evidencing the importance of the possibility to reduce the risk of food alteration in cold smoked salmon industry and to prevent the replication of L. monocytogenes using autochthonous microorganisms with a potential biopreservative action. Moreover, in the second study, strains of Lactobacillus animalis and L. paracasei subsp. paracasei, never studied before for bioprotective purpose and characterized by limited knowledge regarding their antagonistic properties, showed promising antimicrobial activity in vitro. This action against a wide number of spoilage and pathogenic bacteria was detected both when the strains were used singularly and was more evident when they were applied as mixture (especially when L. paracasei subsp. paracasei was predominant). The antagonistic effect was due mainly to the competition for nutrients and to the production of organic acids (acetic and lactic) as combined effects. In the third study, two multistrain mixtures (L. sakei mixture and especially L. curvatus mixture), obtained adding different strains isolated and identified from Argentine vacuum packed meat, showed a promising antimicrobial activity against a wide number of spoilage and pathogenic bacteria, highlighting that the antagonistic effect originates probably from the nutrient competitive exclusion and the possible production of metabolites such organic acids. Moreover, the addition of the two mixtures to sliced vacuum-packed beef determined a better microbial quality of meat as TVC, Enterobacteriaceae and Gram negative bacteria resulted lower if compared to control samples. In any case, if compared with in vitro results, a slighter effect was detected on beef samples; it was probably due to the different competitiveness of the cultures if applied to a complex substrate like meat and to the buffering capacity of meat. The fourth study was focused on the application of organic acids and salts on non-prepacked hamburgers, as they are known to exert potential benefits in terms of bacterial inhibition and stabilization of sensory characteristics. The addition of mixtures containing sodium ascorbate, sodium citrate and sodium acetate was effective in microbial inhibition of non-prepacked beef hamburgers, especially when the highest acetate dose was used. An evident activity was found against Gram negative bacteria, which represent the most important microorganisms in determining the shelf-life of raw minced meat. This, associated with lower TVB-N values, resulted in an improvement in the hygienic quality of treated samples. These salts are now admitted only for “prepacked meat preparations” but the results evidenced the convenience for butchers to extend the use of these organic salts to non-prepacked minced meat preparations as an additional means to ensure product safety and shelf-life. In conclusion, the two technologies tested in these studies resulted to be promising as an evident antimicrobial effect was confirmed, suggesting the possibility to apply these tools to extend the shelf-life of food.