Oxygen Addition and Sterol Synthesis in Saccharomyces cerevisiae during Enological Fermentation

Abstract

Under anaerobic conditions, yeast growth normally requires oxygen in order to favour the synthesis of sterols and unsaturated fatty acids. However, in such conditions, superfluous oxygen consumption by yeast cells is observed. The superfluous oxygen consumed by the yeast cells appears to be not related to classical respiration, but mainly to the operation of several alternative oxygen consumption pathways. In this study, the potential relationship between this superfluous oxygen consumption and the yeast sterol synthesis pathway was investigated during enological fermentation. Additions of small (7 mg l(-1)) and excess (37 mg l(-1)) amounts of oxygen at the end of cell growth phase were used as a method of comparing oxygen consumption by normal synthetic pathways with that by alternative respiration pathways. The superfluous oxygen consumption by yeast cells during fermentation seemed not to alter and strongly favoured fermentation kinetics and cell biomass formation. However, a marked decrease of the orderliness of the membrane phospholipids is observed, which is not related to the drop of cell viability. After oxygen additions, squalene contents of the cells decreased, while the relative proportions of ergosterol or its precursors in the total sterol fraction did not correlatively increase. It was further found that an oxygen-dependent sterol degradation occurred when oxygen was added in excess amounts with respect to the cellular requirements for sterol synthesis. At present, this modification of the sterol contents of yeast membranes has not been related to any physiological parameters.

Influence of stressful fermentation conditions on neutral lipids of a Saccharomyces cerevisiae brewing strain

“…An increased squalene accumulation was also noted in S. cerevisiae wine strains (Mannazzu et al 2008), which suggests inhibition of sterol synthesis in a sugar rich medium such as malt wort and grape must. According to several authors, the cell ergosterol content between 0.4 and 0.8 mg g -1 dry biomass in Saccharomyces cerevisiae is sufficient for the complete sugar consumption in a sugar-rich medium (Valero et al 2001;Fornairon-Bonnefondb et al 2002;Belviso et al 2004) and is adequate for a complete fermentation (Zara et al 2008). In our study, all investigated yeast generations maintained the ergosterol content in this range (Table 1).…”

Effect of oxygen and lipid supplementation on the volatile composition of chemically defined medium and Chardonnay wine fermented with Saccharomyces cerevisiae

“…However, under anaerobic fermentation conditions molecular oxygen or anaerobic growth factors in the form of exogenous lipids, such as ergosterol and unsaturated fatty acids (UFAs), are needed to promote adequate growth to enable complete fermentation of highly clarified grape must (Alexandre & Charpentier, 1998;Bisson, 1999;Blateyron & Sablayrolles, 2001;Houtman & du Plessis, 1986;Ingledew & Kunkee, 1985;Larue & Lafon-Lafourcade, 1989;Rosenfeld, Beauvoit, Blondin, & Salmon, 2003). Indeed, lack of oxygen and lipids in anaerobic growth media causes stress for yeast cells and inhibits cell growth (Bardi, Crivelli, & Marzona, 1998;Deytieux, Mussard, Biron, & Salmon, 2005;Fornairon-Bonnefond, Demaretz, Rosenfeld, & Salmon, 2002). In anaerobiosis long-chain saturated fatty acids accumulate in the cell and inhibit acetyl-CoA carboxylase and prevent fatty acid elongation by the fatty acid synthase (FAS) complex (Schweizer, 1984;Wakil, Stoops, & Joshi, 1983).…”

“…Furthermore, unsaturation of long-chain fatty acids is prevented by presumed inhibition of fatty acid desaturase by high sugar and the requirement for molecular oxygen (Salmon, Fornairon, & Barre, 1998). In addition, several intermediates of the ergosterol biosynthetic pathway, such as squalene, lanosterol and zymosterol, accumulate due to the inhibition of this pathway by anaerobiosis (Belviso, Bardi, Bartolini, & Marzona, 2004;Fornairon-Bonnefond et al, 2002;Mannazzu et al, 2008). Thus, fatty acids and sterols are not only essential for maintaining membrane integrity and function (Cartwright, Rose, Calderbank, & Keenan, 1989;Henschke & Rose, 1991) and consequently yeast cell viability and fermentation activity, but also for adaptation to fermentation stresses, such as high sugar and ethanol toxicity, which can increase cell requirement for lipids (Aguilera, Peinado, Millan, Ortega, & Mauricio, 2006;Chi & Arneborg, 1999;Hammond, 1993;Ratledge & Evans, 1989).…”

Interactions between yeast, oxygen and polyphenols during alcoholic fermentations: Practical implications

“…In vitro, these are associated with a massive production of reactive oxygen species (ROS), particularly H 2 O 2 and O 2 dÀ . Also, when excessive levels of oxygen are added to yeast cells during enological fermentations, cell sterol content decreases, following the strong oxidation of ergosterol into oxidized sterols (Fornairon-Bonnefond, Desmaretz, Rosenfeld, & Salmon, 2002).…”