Characterization of potential probiotic bacteria from table olives fermentations: towards a new functional food

The gastrointestinal tract (GIT) has always been considered as main source of probiotic bacteria. However, many studies have recently focused on lactic acid bacteria (LAB) isolated from foodstuffs. The selection of beneficial LAB strains in the field of dairy foods has been widely investigated, whereas the identification of new probiotic strains from fermented vegetables is just at the beginning. In this contest, table olives could be considered as a suitable source of probiotics and a good carrier for them, since their autochthonous LAB microbiota is mainly composed by Lactobacillus (Lb.) plantarum, a species with a well documented beneficial effect for human GIT. Anyhow, even if the species of origin is well known, the development of a new potential probiotic must start from an accurate study of the safety features and beneficial roles of each strain selected. Therefore, the aim of this research was the identification of potential probiotic LAB strains isolated from table olives and their subsequent introduction in the same matrix of origin, in order to develop a new functional food. With this purpose, 293 strains of LAB, isolated from industrial and laboratory fermentations of green table olives, were subjected to a simulation of human digestion process. This first screening allowed to collect a narrow group of strains, which were identified by species specific PCR and subsequently typed by means of REP-PCR. Safety of the selected strains was assessed considering both their potential resistance to common antibiotics and the undesirable metabolic potentiality to produce biogenic amine (BA). Strains were checked for cytotoxicity as well as adhesion capability, both in 2D and 3D intestinal model which were made using H4 human epithelial cells. The 3D model is an in vitro method which closely mimics the intestinal lumen shape and through the measurement of its transepithelial electrical resistance (TEER) we could understood the direct interaction between bacteria and epithelial cells. In parallel, exploiting the 2D model the potential inhibition of Listeria (L.) monocytogenes infection were analyzed. Finally, to highlight the technological potentialities of the selected strains we evaluated their adhesiveness on the table olives surface. All data were subjected to ANOVA and Duncan???s test. Overall, 17 strains were chosen due to their resistance in a simulation of human digestion. The majority of them belonged to Lactobacillus (Lb.) plantarum and showed a low intraspecific biodiversity by means of REP-PCR. All strains are recognized as not harmful since neither production of BA nor cytotoxic effect versus human cells were detected. Two Lb. plantarum strains (S1T10A and S11T3E) enhanced significantly the integrity of the polarized epithelium (P<0.05). Moreover, S11T3E showed the ability to inhibit the L. monocytogenes invasion in 2D epithelial model (P<0.05). Concerning the technologic properties, strains Lb. plantarum S11T3E and O2T60C showed the greater adhesiveness on the table olives surface. In conclusion, Lb. plantarum S11T3E could be considered the most promising candidate for the development of a new functional food, the probiotic table olives.