Biotechnology Letters 22: 1947–1951, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 1947 Evaluation of stereoisomers of 2,3-butanediol and acetoin to differentiate Saccharomyces cerevisiae and Kloeckera apiculata wine strains P. Romano 1,∗ , G. Palla 2 , A. Caligiani 2 , V. Brandolini 3 , A. Maietti 3 & G. Salzano 1 1 Dipartimento di Biologia, Difesa e Biotecnologie Agro-Forestali, Universit` a della Basilicata, Contrada Macchia Romana, 85100 Potenza, Italy 2 Dipartimento di Chimica Organica e Industriale, Universit` a di Parma, Parco Area delle Scienze 17A, 43100 Parma, Italy 3 Dipartimento di Scienze Farmaceutiche, Universit` a di Ferrara, Via Fossato di Mortara 17/19, 44100 Ferrara, Italy ∗ Author for correspondence (Fax: +39 0971 205576; E-mail: pot2930@iperbole.bologna.it) Received 9 August 2000; Revisions requested 22 August 2000; Revisions received 5 October 2000; Accepted 6 October 2000 Key words: acetoin, 2,3-butanediol, Kloeckera apiculata, Saccharomyces cerevisiae, wine Abstract The (R)/(S) ratios of acetoin were always higher in wines obtained by Saccharomyces cerevisiae than in those obtained by Kloeckera apiculata. A significantly different behaviour was determined between the two species as regards contents and ratios of 2,3-butanediols: S. cerevisiae produced more (R,R)-2,3-butanediol (about 80%), whereas K. apiculata produced more meso-form (about 90%). Introduction Wine-making has turned increasingly to a well- controlled process with extended microbiological in- vestigations on the alcoholic fermentation. As wine quality is also a consequence of the diversity and the composition of microorganisms, it is important to recognize the different wine yeasts involved in the process. Among the numerous methods to study wine yeasts, the strain determination for by-product formation has been used successfully to differentiate different yeast genera involved in wine fermentation (Zironi et al. 1993, Romano 1996, 1998). The charac- terization of a large number of strains for by-product formation has underlined that the yeast species itself is a prominent factor in determining the wine com- position (Houtman et al. 1980, Benda 1982, Herraiz et al. 1990, Romano et al. 1996). Among other fac- tors, 2,3-butanediol, formed during fermentation of carbohydrates, is an important constituent of wine and affects the quality of the final product. Strains of the species Saccharomyces cerevisiae will produce from 200 to 900 mg 2,3-butanediol l −1 in wine, whereas apiculate yeasts produce low amounts, from about 50 to 220 mg l −1 (Herold et al. 1995, Romano et al. 1998). In this study, we have developed a method to es- timate the enantiomers 2,3-butanediol [R,R; S,S; R,S (meso-form)] and (R,S)-acetoin, formed during alco- holic fermentation to differentiate strains of differ- ent wine species, such as Kloeckera apiculata and S. cerevisiae. The enantiomeric ratio of acetoin is also con- sidered important and has been proposed to distin- guish between common and traditionally aged vine- gars (Chiavaro et al. 1997). As regards butanediols, the production is also affected by several fermenta- tion parameters (Garg & Jain 1995) and a very high content has been determined in high-quality wines (Sponholz et al. 1993). The interest in the field encour- aged us to investigate on the quality and quantity of the C-4 metabolites occurring during wine fermentation performed by different wine yeasts.