Isolation of Saccharomyces cerevisiae strains from different food matrices and their preliminary selection for a potential use as probiotics

To isolate acid- and bile-resistant Saccharomyces cerevisiae strains directly from food samples and to preliminarily select them on the basis of fundamental probiotic properties. A rapid screening method allowed the isolation and selection of 20 acid- and bile-resistant yeasts from foods, avoiding time-consuming isolation steps. The strains were characterized for their specific survival in simulated gastric juice and in intestinal fluid after pre-exposure at low pH. Ten isolates demonstrated a satisfactory survival percentage in intestinal fluid after pre-exposure to gastric juice and appreciable lipolytic and proteolytic properties, as demonstrated by the API-ZYM test. By using molecular methods five strains were identified as Saccharomyces cerevisiae, three as Candida spp., one as Candida pararugosa and one as Pichia spp. The Saccharomyces cerevisiae strains showed considerable probiotic properties, achieving a 80 < % < 90 survival through the simulated gastrointestinal tract, as well as interesting glucosidase activities. The research represents an efficient strategy to select and identify Saccharomyces cerevisiae strains with desirable acid and bile resistances. This paper reports the direct selection of potentially probiotic yeasts from foods and provides indications about the ability of Saccharomyces cerevisiae strains to survive conditions simulating the human gastrointestinal tract.