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RESEARCH PRODUCT

Exoenzymes of Wine Microorganisms

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The production of wine from grape juice is predominantly the result of enzymatic reactions. The enzymes originate from the grape itself, from epiphytic fungi like Botrytis cinerea colonizing the grape surface and finally from yeasts and bacteria growing in the must until termination of alcoholic fermentation. Especially nonSaccharomyces yeasts, also called “wild” yeasts, belonging to the genera Kloeckera, Candida, Debaryomyces, Rhodotorula, Pichia, Zygosaccharomyces, Hanseniaspora, Kluyveromyces, and Metschnikowia produce and secrete several enzymes (esterases, glycosidases, lipases, glucanases, proteases, cellulases, etc.) to the periplasmatic space and the medium where they may interact with grape precursor compounds to produce aroma active compounds (Charoenchai et al. 1997). Apart from yeasts, lactic acid bacteria play an import for vinification, i.e., the genera Oenococcus, Leuconostoc, Pediococcus, Lactobacillus, and Weissella (Wibowo et al. 1985; Fugelsang and Edwards 2007; see also Chap. 1). Because of its vitality under the extreme life conditions of wine (pH 3.0–4.0; alcohol concentration 10–15%), Oenococcus oeni is the primary species responsible for the malolactic fermentation. After completion of alcoholic fermentation, the malolactic enzyme catalyzes the conversion of the dicarbonic acid l-malate to the monocarbonic acid l-lactate and CO 2 . The result is a biological acid reduction which is often preferable in white wines. On the opposite, Lactobacillus and Pediococcus are more active in the early stages of vinification often in connection with stuck fermentations and wine spoilage (Fugelsang and Edwards 2007). A considerable number of publications emphasize the importance of hydrolytic enzymes from lactic acid bacteria for the winemaking process and its control (Matthews et al. 2004, 2006, 2007; Claus 2007). Proteases, e.g., have been found in wine-associated strains of Lactobacillus and Oenococcus (Manca de Nadra et al. 1997,