Effect of Lipids and Oxygen on Yeast Growth and the Biosynthesis of Acetoin During Fermentation

Abstract

Brewery yeast needs traces of oxygen for the biosynthesis of unsaturated fatty acids and ergosterol. Owing to the increase in cell mass during primary fermentation the concentrations of these essential lipids decrease and thereby affect the physiological condition of the yeast. When the sterol concentration of whole cells has decreased to 0-2 to 0-3 mg per 100 tng dry yeast, the yeast changes its metabolism. This metabolic change is revealed by a decrease in acetoin con centration. The absorption of wort nutrients and consequently the efficiency of growth is at this point also greatly reduced. The ratio between yeast growth and mole ethanol formed (i.e. the molar growth yield) decreases greatly during wort fermentation. A close correlation between molar growth yield and the change in acetoin metabolism can be observed. This metabolic change occurs when the ratio between yeast growth and ethanol formed is in the range of 8-3 to 9-1, averaging 8-7 g/mole.

Nutrient Exchange of Carbon and Nitrogen Promotes the Formation of Stable Mutualisms Between Chlorella sorokiniana and Saccharomyces cerevisiae Under Engineered Synthetic Growth Conditions

“…Of the monitored metabolites, succinic acid, which is produced during the tricarboxylic acid cycle by fermenting yeasts during the exponential and stationary growth phase, was produced during stationary phase along with glycerol and ethanol (Heerde and Radler, 1978; Arikawa et al, 1999). The oxygen produced by the microalga was rapidly respired by the yeast (Haukeli and Lie, 1976) as evidenced by the rapid decline in dissolved oxygen during the exponential growth of S. cerevisiae. In turn, this has a positive impact on the microalgae as oxidative stress is reduced, thus negating the inhibition of microalgae growth, and biomass production (Ugwu et al, 2007; Raso et al, 2012; Li et al, 2017).…”

Relationship between Ergosterol Concentrations in Wine Yeast and Sugar Fermentation at Different Temperatures

“…1). Further growth of the yeasts in this study could well have been inhibited by a growth-limiting concentration of approximately 0, 1 % ergosterol (David & Kirsop, 1973;Haukeli & Lie, 1976;Aries & Kirsop, 1977) as this compound is not produced under anaerobic conditions, as well as by the ethanol in the medium. The lower ergosterol concentrations at the higher temperatures are ascribed to the higher growth rate of the yeast cells resulting in a more rapid dilution of the ergosterol.…”

“…cerevisiae under anaerobic conditions results in requirements for both a sterol and an unsaturated fatty acid. However, growth rates similar to those found under aerobic conditions can be maintained under anaerobic conditions if the medium is supplemented with ergosterol and oleic or linoleic acid (Haukeli & Lie, 1976;Watson & Rose, 1980). The endogenous levels of unsaturated fatty acids and sterols in Sacch.…”