Strengthening of Cell Wall Structure Enhances Stress Resistance and Fermentation Performance in Lager Yeast

Brewing condition exposes lager yeast to a continuous mix of stresses, which decreases cell viability and fermentation efficiency. Recent studies have indicated the close correlation between strain stress resistance and cell wall modification. Here, using micafungin as the selection marker, two stress-resistant mutants, MR0-8 and MR1-2, with thickened cell walls, were screened via traditional UV mutagenesis strategy. Quantitative analysis of cell wall components in MR0-8 and MR1-2 showed 64% and 52% higher glucan contents, 26% and 33% higher mannan contents, and 34% and 31% higher chitin contents, respectively, than those in the parent strain. During high-gravity brewing, the mutant strains showed efficient fermentation rates, increased cell viabilities, and increased intracellular trehalose levels compared with those of the parent strain. Meanwhile, beers fermented by the mutants had balanced flavor profiles and lower contents of diacetyl than those of the parent strain fermented beer. Moreover, levels of protease A released from mutants under nutrient limitation stress were 0.5-fold of that from the parent strain. In summary, strengthening cell wall structure improved stress resistance and the newly screened strains showed great potential in high-gravity brewing.