Generation of odorous acyloins by yeast pyruvate decarboxylases and their occurrence in sherry and soy sauce

Volatile acyloins (alpha -hydroxy ketones) were obtained by condensing eith er aldehydes with pyruvate or 2-keto acids with acetaldehyde in a reaction catalyzed by yeast pyruvate decarboxylases (EC 4.1.1.1). Odor qualities and threshold values of 34 acyloins were evaluated, and 23 of them possessed d istinct flavor properties. Sherry and soy sauce flavors were analyzed: 2-hy droxy-3-pentanone and 3-hydroxy-2-pentanone were identified in soy sauce fo r the first time; these and 2-hydroxy-5-methyl-3-hexanone and 3-hydroxy-1-p henyl-2-butanone were isolated from sherry for the first time. The biocatal ytic efficiencies of crude pyruvate decarboxylase preparations from Zygosac charomyces bisporus, Saccharomyces cerevisiae, Kluyveromyces lactis, and Kl uyveromyces marxianus were compared. Product yields comparable to those of conversions with purified pyruvate decarboxylase demonstrated the suitabili ty of crude enzyme extracts as cost-effective biocatalysts in acyloin forma tion. Conversion rates of > 50% showed that the potential of this type of e nzyme to catalyze the formation of aliphatic acyloins has been underestimat ed before.