Growth and physiology of Dekkera/Brettanomyces yeast and the production of flavour impact compounds in wine

Abstract

Volatile phenols are produced by Dekkera yeasts and are critical in wine spoilage. The growth and substrae utilisation rates of Dekkera species differed depending on strain and the acid precursor present.

Summary

Dekkera and Brettanomyces yeast are important spoilage organisms in a number of food and beverage products. Isolates of both genera were cultured in defined medium, supplemented with hydroxycinnamic acids (HCAs) and vinylphenols to investigate their influence on growth and the formation of ethyl phenol derivatives. The growth rate of Brettanomyces species in the presence of acids was reduced and no significant conversion to vinyl or ethyl derivatives was observed. The growth rate and substrate utilisation rates of Dekkera anomala and Dekkera bruxellensis yeast differed depending on strain and the acid precursor present. Growth of D. bruxellensis was slowed by the presence of ferulic acid with the addition of 1 mM ferulic acid completely inhibiting growth in chemically defined media. The microbial synthesis of volatile phenols is thought to occur in two steps via the enzyme phenolic acid decarboxylase (PAD) converting HCAs to vinyl derivatives, which are the substrates of a second enzyme, postulated to be a vinylphenol reductase (VPR) whose activity results in the formation of ethylphenols.

Both steps of the pathway were investigated, using cell extracts from a numberof Dekkera and Brettanomycesspecies. Dekkera species catabolise ferulic, caffeic and p-coumaric acids and possess inducible enzymes with similar pH and temperature optima. Brettanomyces does not decarboxylate HCAs but does breakdown vinylphenols. A partial protein sequence for PAD was determined from Dekkera anomala and may indicate the presence of a novel enzyme in this genus. The effect of ferulic acid additions on Dekkera growth was investigated under various wine-related conditions and in combination with other hydroxycinnamic acids, namely p-coumaric and/or caffeic acids. The growth of Dekkera yeast species was inhibited by ferulic acid and this effect was enhanced in the presence of ethanol. In wine the concentration of ferulic acid required to inhibit or kill Dekkera is significantly reduced.