Potentiality of yeast strains isolated from beer starters and brewing fermentation residues to be used as probiotics

Abstract

The aim of this work was to study the potential probiotic properties of yeast strains isolated from brewer´s starters. Beer is the most popular alcoholic beverage worldwide, and the third-most popular drink overall after water and tea. During brewing wort fermentation, yeast biomass increases largely, obtaining a high nutritional by-product, today considered waste. From twelve brewer´s starters, we selected M6 starter and its two constituent strains, Saccharomyces cerevisiae and Pichia kudriavzevii, which showed the highest resistance to gastrointestinal (GI) conditions in vitro. The consortium and its isolates proved to be capable to bind aflatoxin B1 (AFB1), a potent carcinogenic compound naturally produced by Aspergillus flavus and Aspergillus parasiticus on agricultural substrates, such as corn. The highest toxin binding capability in vitro was observed when the isolates were grown in brewer´s wort (80 %), while YPD broth cultures (yeast extract 10 g/l, peptone 20 g/l, dextrose 20 g/l) only bound 20% or less of the initial AFB1 concentration (300 ppb) (detected by Aflatoxin competitive direct ELISA test Veratox®, NeogenCorporation, USA). De-adsorption of AFB1 during in vitro GI passage was also evaluated in brewing fermentation residues (BFR), and no more than 26% of the initial mycotoxin concentration (300 ppb) was detected in supernatants, remaining more than 50% of toxin strongly bound to BFR. Finally, we observed a decrease of the cytotoxic effect of AFB1 (500 ppb) on HepG2 cells to levels similar to those to the negative controls (HepG2 cells in Dulbecco´s modified Eagle´s medium - DMEM - without AFB1). It is remarkable that yeasts grown in brewer´s wort showed better potential probiotic properties than the yeasts grown in a nutritive balanced designed microbiological medium, like YPD broth. These results suggest the brewery´s wastes potential as a high-value nutritional and probiotic by-product.