Impact of non-Saccharomyces yeasts derived from traditional fermented foods on beer aroma: Analysis based on HS-SPME-GC/MS combined with chemometrics.

In recent years, numerous studies have demonstrated the significant potential of non-Saccharomyces yeasts in aroma generation during fermentation. In this study, 134 strains of yeast were isolated from traditional fermented foods. Subsequently, through primary and tertiary screening, 28 strains of aroma-producing non-Saccharomyces yeast were selected for beer brewing. Headspace-solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and chemometrics were employed to analyze the volatile flavor substances in beer samples fermented using these strains. Chemometric analysis revealed that distinct species of non-Saccharomyces yeast had a unique influence on beer aroma, with strains from the same genus producing more similar flavor profiles. Accordingly, 2,6-nonadienal, 1-pentanol, phenyl ethanol, isoamyl acetate, ethyl caprate, butyl butyrate, ethyl propionate, furfuryl alcohol, phenethyl acetate, ethyl butyrate, ethyl laurate, acetic acid, and 3-methyl-4 heptanone were identified as the key aroma compounds for distinguishing among different non-Saccharomyces yeast species. This work provides useful insights into the aroma-producing characteristics of different non-Saccharomyces yeasts to reference the targeted improvement of beer aroma.

Reduced sensitivity of lager brewing yeast to premature yeast flocculation via adaptive evolution.

Malt-induced premature yeast flocculation (PYF) is a sporadic problem within the brewing industry. The use of PYF malts is concomitant with a number of negative impacts on beer quality, including incomplete fermentation and/or flavor defects. Although malt-induced PYF is widely acknowledged, actions taken so far have proved insufficient to solve the PYF-related issues. To limit the detrimental effects of PYF malts on beer production, an adaptive laboratory evolution (ALE) process was applied in this study to an industrial lager brewing yeast strain (TT02), in an attempt to generate variant strains with improved fermentation performance in PYF wort. Through a batch fermentation-based adaptation process, evolved variants were isolated and screened for their phenotypic and metabolic traits. The investigation focused mainly on the tendency to remain in suspension, fermentation capacity and final acetaldehyde concentration. We successfully obtained a variant (TT02-30 T) with improved fermentation properties. The improvement was seen in worts prepared from different types of PYF malt as well as normal malt. Furthermore, ALE of lager brewing yeast in PYF wort yielded a wide array of mutations. Several changes in the genomes (copy number variation in flocculin encoding gene FLO1 and a missense SNP in a putative mitochondrial membrane protein coding gene FMP10) of the variant strains relative to the original strain were observed. These could potentially contribute to the improved yeast suspension during fermentation. Importantly, mutational enrichment in genes related to ion binding in PYF-evolved strains suggests the involvement of the yeast ion transportation process in dealing with the PYF stress. Our study demonstrates the possibility of attenuating yeast sensitivity to PYF malts over time through adaptive laboratory evolution via spontaneous mutation.