Evaluating the probiotic potential and technological characteristics of yeasts implicated in cv. Kalamata natural...

In the present study, 49 yeast strains previously isolated from cv. Kalamata table olive fermentation were assessed for their probiotic potential and technological characteristics. The probiotic assays included the in vitro survival in simulated gastric and pancreatic digestions, surface adhesion to the intestinal cell line Caco-2, hydrophobicity, autoaggregation and haemolytic activity. The technological features of the strains were also elucidated in terms of enzymatic activity and susceptibility to diverse salt levels (0-250 g/L) and pH values (3.5, 5.0, and 6.5). The obtained results indicated that during the simulated gastric and pancreatic digestions, 42 out of the 49 yeast strains presented overall survival rate higher than 50%, while 24 strains showed survival percentage higher than 70% at the end of the digestions. Furthermore, the majority of the assayed strains presented hydrophobicity percentage higher than 75%, while the autoaggregation ability ranged between 72 and 91%. None of the strains showed haemolytic activity. The majority of the strains presented high tolerance to salt with some strains exhibiting tolerance even at salt concentrations higher than 200 g/L. Concerning the enzymatic activity, 45 strains presented valine and cystine arylamidase activity, while positive reactions for the enzymes β- and α-glucosidase were observed for 27 and 14 strains, respectively. Moreover, 11 strains presented α-galactosidase and alkaline phosphatase activity. From the total number of studied yeasts, the strain Y34 belonging to Saccharomyces cerevisiae presented positive results in the majority of both probiotic and technological assays and thus it could be considered a potential starter either as single or as combined culture with lactic acid bacteria in the fermentation of Greek-style natural black olives.