Screening and characterization of organic-Se enriched yeasts via engineering combined lab-adaptive evolution strategies to produce fragrant cider.

Saccharomyces cerevisiae can biotransform selenium (Se) into low-toxicity and easily absorbed organic-Se forms, but a comprehensive analysis of its Se-enriched properties and Se-enriched fermentation performance is lacking. In this study, the engineered mutant yeast 6# (EMY6#) was obtained by using an engineered mutagenesis strategy. Its Se-enriched properties, Se cellular localization, Se morphology, and effects on the quality of fragrant cider were analyzed. The results indicated that the total Se content of Se-enriched EMY6# (SeREMY6#) increased to 2616.92 mg/kg, and the proportion of organic-Se increased to 94.5 %. Se cellular localization showed that organic-Se was mainly localized in the cytoplasm (94.87 %) and proteins (95.71 %), and the primary Se forms were SeMet (53.62 %), SeCys (17.33 %) and SeMecys (15.61 %). Meanwhile, exogenous Se resulted in a significant increase in selenophosphate synthase activity of the EMY6# strain. Furthermore, SeREMY6# fermentation increased the content of polyphenols, flavonoids, and aromatic compounds in cider by 1.5, 1.95, and 2.02 times, respectively. Notably, ethyl caprylate, 2-methylbutyl acetate, and ethyl 9-decenoate were the key volatile flavor compounds in SeREMY6#-fermented cider, which could give the cider a distinctive fruity and rosy aroma. In addition, SeREMY6#-fermented cider had the highest Se content with 20.663 μg/L total Se and 15.387 μg/L organic-Se, as well as obtaining the best sensory acceptability. These findings make SeREMY6# promising as a Se-enriched starter and Se-supplement in the fermentation of cider.