Lactic Acid Bacteria as Bioprotective and Health-Promoting Cultures in the Food Industry

In this PhD thesis, the potential of lactic acid bacteria (LAB) as bioprotective and health-promoting cultures in the food industry was investigated. The first part of this PhD thesis was focused on the bioprotective activity of LAB in seafood products. The foodborne pathogen Listeria monocytogenes intentionally inoculated in cold-smoked sea bass was effectively inhibited by one of the LAB cultures tested. The product inoculated with LAB did not lead to the development of any off odor and off flavor. Some of the LAB cultures tested resulted to be also able to control the spoilage microflora of sea bass and sea bream burgers, avoiding bloating spoilage. This results in an extension of the shelf life of fish burgers, which, as it is well known, are highly perishable. In this case, bioprotective cultures had produced some changes in the sensory profile of the product, however, the inoculated burgers resulted to be preferred by the sensory panel compared to the control (without LAB inoculation). These results demonstrated the potential use of bioprotective cultures to improve the quality and safety of fishery products, contributing to the reduction of food waste in the fish supply chain. The second part of this PhD thesis was focused on the study of the probiotic properties of several strains belonging to Lacticaseibacillus casei, Lacticaseibacillus paracasei and Lacticaseibacillus rhamnosus species, previously isolated and characterized. Many of the tested strains showed potential probiotic properties, in particular, they were able to efficiently adhere to intestinal epithelial cells which is an essential requirement to play a beneficial role in the intestinal tract. Heat-killed (HK) cells and cell-free supernatants (CFS) derived from several probiotic strains were tested for their potential antiproliferative activity against colorectal cancer cells. Results revealed that HK cells did not have any significant effect on cancer cell viability. On the contrary, a significant antiproliferative effect of the CFS extracellular metabolites produced by all the strains was observed, regardless of pH and in a time-dependent manner. This constitutes a starting point for the future individuation and characterization of the metabolite/s is/are responsible for the antiproliferative effect. Understanding the mechanism involved in the reduction of cell viability is also fundamental for the potential application of these compounds for therapeutic applications. The ability of LAB to produce membrane vesicles (MVs). Probiotic-derived MVs are gaining interest for their possible use in the treatment of diseases using them as therapeutic carriers since evolving evidence is demonstrating their beneficial effects on human health. Two type strains belonging to L. paracasei and L. rhamnosus species resulted to be able to produce a considerable amount of MVs which were subsequently characterized. The size distribution of MVs was measured using two different techniques (Nanoparticle Tracking Analysis and Atomic Force Microscopy). LpMVs resulted to have a lower size compared to those produced by L. rhamnosus, although the formers were higher in number. Fatty acids analysis revealed that, according to the literature, MVs derive from the cytoplasmic membrane of Gram-positive bacteria since the main abundant FAs were the same for both MVs and parental bacterial cells. Proteins and RNA quantifications demonstrated that these two classes of components are present in MVs, and, in the future, proteomic and transcriptomic analyses will be performed with the aim to contribute to understanding the biological function of MVs. The association of beneficial effects to the cellular components or extracellular metabolites of probiotic bacteria will limit, at least in part, the use of the live probiotics, avoiding the risks associated with the administration of live organisms.