Molecular, pro-technological and functional characterization of yeasts isolated from Tuscan sourdoughs to be used as potential starters

Yeast populations of traditional sourdoughs collected from four Tuscan bakeries were investigated. Among 200 isolated strains, 81 were randomly selected and molecularly characterized. Saccharomyces cerevisiae was dominant, representing the only species detected in three out of the four sourdoughs. The fourth one harboured also Kazachstania humilis. Inter-delta regions analysis revealed a high intra-specific polymorphism discriminating 18 biotypes among the 80 S. cerevisiae isolates, which clustered based on their origin. Twenty representative isolates of the biotype groups were singly used to ferment soft and durum wheat flour, aiming at evaluating the main pro-technological and functional properties. During fermentation under standardized conditions, all strains were able to grow of ca. 2 log cycles but only S. cerevisiae L10Y, D18Y and D20Y had a significantly shorter latency phase in both the flours. Strains D5Y, D8Y, D9Y, D12Y, D20Y and D24Y caused the highest dough volume increase. K. humilis G23Y was the only strain able to increase the total free amino acids concentration of the doughs. K. humilis G23Y and S. cerevisiae D20Y and D24Y were characterized for a phytase activity more than three times higher than spontaneously fermented control. Although without relevant differences among them, almost all the strains led to the increase of the antioxidant activity. Besides the evaluation of the properties related to bakery applications, the resistance of the strains to simulated gastric and intestinal conditions, that is considered a pre-requisite for the selection of probiotics, was also investigated, revealing a relevant in vitro survival for many of the strains considered.