Residual mitochondrial transmembrane potential decreases unsaturated fatty acid level in sake yeast during alcoholic fermentation

Abstract

Oxygen, a key nutrient in alcoholic fermentation, is rapidly depleted during this process. Several pathways of oxygen utilization have been reported in the yeast Saccharomyces cerevisiae during alcoholic fermentation, namely synthesis of unsaturated fatty acid, sterols and heme, and the mitochondrial electron transport chain. However, the interaction between these pathways has not been investigated. In this study, we showed that the major proportion of unsaturated fatty acids of ester-linked lipids in sake fermentation mash is derived from the sake yeast rather than from rice or koji (rice fermented with Aspergillus). Additionally, during alcoholic fermentation, inhibition of the residual mitochondrial activity of sake yeast increases the levels of unsaturated fatty acids of ester-linked lipids. These findings indicate that the residual activity of the mitochondrial electron transport chain reduces molecular oxygen levels and decreases the synthesis of unsaturated fatty acids, thereby increasing the synthesis of estery flavors by sake yeast. This is the first report of a novel link between residual mitochondrial transmembrane potential and the synthesis of unsaturated fatty acids by the brewery yeast during alcoholic fermentation.

Chromosomal Aneuploidy Improves the Brewing Characteristics of Sake Yeast

“…Because mitochondria shrink in response to oxygen starvation (31), the mitochondria of brewery yeast during alcoholic fermentation are believed to have a low activity during alcoholic fermentation. In contradiction to this notion, we have found that residual mitochondrial activity of brewery yeasts has as a major role in organic acid (32) and fatty acid (33) metabolism and the degradation of mitochondria during alcoholic fermentation has an important role in brewing progression (34). Moreover, the variety in the mitochondrial activity of sake yeasts is a critical factor governing its brewery profile (35).…”

Methionine and Glycine Stabilize Mitochondrial Activity in Sake Yeast During Ethanol Fermentation

“…The results obtained in this study suggest that the specific amino acids generated during sake brewing affect the mitochondrial activity of sake yeast and thus its brewing profiles. Since the regulation of mitochondria in brewer's yeasts affects hydrogen sulfide formation (13), diacetyl formation (14), fermentation ability (15), volatile ester formation (16), fatty acid desaturation (17), and malate and succinate production (18), many brewers attempt to manipulate the mitochondrial activity of brewer's yeasts by oxygenation. The results obtained in this study suggest that amino acid supplementation might act as a new approach to manipulate mitochondrial activity in brewer's yeasts.…”

“…Molecular oxygen breaks down rapidly upon fermentation, leading to rapid loss of mitochondrial activity. However, we and other groups have reported that residual mitochondrial activity plays significant roles in the fermentation characteristics of brewer's yeasts, such as hydrogen sulfide formation (13), diacetyl formation (14), fermentation ability (15), volatile ester formation (16), fatty acid desaturation (17), and malate and succinate production (18). Furthermore, we have previously shown that mitophagy, the degradation of mitochondria by autophagy (19)(20)(21)(22), plays a significant role in the progression of alcoholic fermentation (15), as observed by the high fermentation ability of atg32Δ sake yeast.…”