Malo-ethanolic fermentation in Saccharomyces and Schizosaccharomyces

Abstract

Yeast species are divided into the K(+) or K(-) groups, based on their ability or inability to metabolise tricarboxylic acid (TCA) cycle intermediates as sole carbon or energy source. The K(-) group of yeasts includes strains of Saccharomyces, Schizosaccharomyces pombe and Zygosaccharomyces bailii, which is capable of utilising TCA cycle intermediates only in the presence of glucose or other assimilable carbon sources. Although grouped together, these yeasts have significant differences in their abilities to degrade malic acid. Typically, strains of Saccharomyces are regarded as inefficient metabolisers of extracellular malic acid, whereas strains of Sch. pombe and Z. bailii can effectively degrade high concentrations of malic acid. The ability of a yeast strain to degrade extracellular malic acid is dependent on both the efficient transport of the dicarboxylic acid and the efficacy of the intracellular malic enzyme. The malic enzyme converts malic acid into pyruvic acid, which is further metabolised to ethanol and carbon dioxide under fermentative conditions via the so-called malo-ethanolic (ME) pathway. This review focuses on the enzymes involved in the ME pathway in Sch. pombe and Saccharomyces species, with specific emphasis on the malate transporter and the intracellular malic enzyme.

Glucose, l-Malic Acid and pH Effect on Fermentation Products in Biological Deacidification

“…These results are consistent with previous studies into the activity of S. cerevisiae (Delcourt et al 1995;Volschenk et al 2003) and S. pombe (Taillandier & Strehaiano 1991).…”

“…Optimal pH for the metabolism of this acid by S. cerevisiae Syrena and S. pombe was 3.0, and 3.5 for hybrid HW2-3. It is known that l-malic acid enters S. cerevisiae cells by simple diffusion and the optimal pH range for this process is 3.0-3.5 (Delcourt et al 1995;Volschenk et al 2003), so the presented findings are consistent with these data. The observed statistically significant changes (P < 0.05) in glycerol formation by S. cerevisiae Syrena and the hybrid HW2-3 were the result of even a slight pH shift from 3.0 to 3.5.…”

“…The production of glycerol gradually increased with glucose concentration in the hybrid HW2-3 cultures. According to the literature, yeast respond to osmotic stress with higher production of glycerol (Groenewald & Viljoen-Bloom 2001;Volschenk et al 2003), which is consistent with the results of the studies presented. The permanent, low concentration of glycerol in the cultures of S. cerevisiae Syrena revealed that this strain was not very sensitive to osmotic stress.…”

Characterisation of Non-Saccharomyces Yeasts Using Different Methodologies and Evaluation of their Compatibility with Malolactic Fermentation

“…The low malic acid utilisation by S. cerevisiae is well documented (Gao & Fleet, 1995;Volschenk et al, 2003;Ribéreau-Gayon et al, 2006). The ability of the nonSaccharomyces strains to degrade malic acid varied greatly and there also were clear differences between the results of the plate and broth assays.…”

Malic Acid Distribution and Degradation in Grape Must During Skin Contact: The Influence of Recombinant Malo-Ethanolic Wine Yeast Strains

“…Commercial wine yeast strains of Saccharomyces have little or no effect on the final L-malic acid concentration in wines, as they are unable to degrade L-malic acid effectively (Radler, 1993;Volschenk et al, 2003). This has been ascribed to the low substrate specificity of the S. cerevisiae malic enzyme and its mitochondrial compartmentalisation, together with the absence of an active transport system for L-malic acid (Volschenk et al, 1997a, b ).…”