Effect of low temperature on Sauvignon blanc fermentation by Saccharomyces cerevisiae

Abstract

Low temperatures greatly influence multiple aspects of Saccharomyces cerevisiae metabolism. Genetically and geographically diverse S. cerevisiae strains show a wide range of growth and fermentation rates at different temperatures (10-30°C) and in different media, but fermentation is an inherent capability of S. cerevisiae at optimal temperatures. The ability to grow well at low temperatures does not correlate with ability to ferment well; however, this correlation can be increased with the addition of sorbitol, suggesting that osmotic stress is an important variable acting on the kinetic variation between strains. The transition from early to mid-late fermentation represents the largest transcriptional response to occur during fermentation, comprising 40 % of the yeast genome. Five key metabolic pathways are strongly influenced by cold fermentation: nitrogen, iron/copper, sulfur, vitamins (biotin and thiamine) and oxidative stress. Yeast strains differ in their transcriptional responses to cold fermentation and have varying degrees of similarity between each other. Transcriptional differences primarily occur between genes involved in the stress response and nutrient utilisation, and these differences are regulated by many transcription factors. Fermentation temperature is one of the most influential variables determining the aromatic profile of New Zealand Sauvignon blanc wines. Contrary to winemakers’ expectations, low temperature fermentation does not necessarily increase volatile concentrations. Low temperature reduces concentrations of the volatile thiol 3-mercaptohexan-1-ol (3MH) and higher alcohol concentrations, in agreement with the literature. The temperature effect on 3- mercaptohexyl acetate (3MHA), esters and fatty acids is largely modified by juice and strain, and these variables interact with one another in a complex manner. Screening for QTLs linked to fermentation Vmax at low temperature proved difficult, because the high amount of biological noise produced by small-scale fermentations prevented the identification of transgressive segregants among backcrossed progeny. However, QTL identification using 123 mapped and phenotyped progeny from a BY4716xRM11-1a cross established that the FLO1 gene on Chromosome I is linked to higher Vmax in the cold in S288c, as the Vmax of the S288c flo1 was decreased by 50 % compared to the S288c FLO1 at 12.5°C. Flo1p may increase Vmax through FLO8-independent cell-substrate interactions induced during stressful conditions such as fermentation.