Influence of SO2 and Zinc on the formation of volatile aldehydes during alcoholic fermentation

Abstract

Laboratório de Análisis del Aroma y Enologia (LAAE). Department of Analytical Chemistry, Faculty of Sciences, Universidad de Zaragoza, 50009, Zaragoza, Spain, During alcoholic fermentation, fusel (or Strecker) aldehydes are intermediates in the amino acid catabolism to form fusel alcohols following the Ehrlich Pathway (1). One of the main enzymes involved in this pathway is Alcohol Dehydrogenase (ADH), whose activity is highly strain dependent and determines the rate of conversion of aldehydes into fusel alcohols (2). This enzyme has a Zn2+ catalytic binding site, which suggests that the must Zn2+ levels will most likely influence the rate of reduction of aldehydes into alcohols. On the other hand, SO2 is commonly used in winemaking for its antiseptic and antioxidant properties. This molecule is highly reactive and can form strong associations (alkylhydroxy sulfonates) with aldehydes. Levels of SO2 present in the alcoholic fermentation could then, at least theoretically, prevent the reduction of aldehydes to alcohols. Aldehydes could accumulate under the form of non-volatile adducts which could be released back once SO2 levels drop with aging or oxidation contributing to the development of oxidation off-odors (3). A set-up of fermentations of synthetic must containing known content of amino acids and nitrogen sources as well as elements necessary to the yeast metabolism were prepared. Different levels of Zinc or SO2 were tested. Three different commercial Saccharomyces cereviase yeast strains were selected for fermentation. Fusel alcohols and Strecker aldehydes were determined in the finished wines by GC-FID and GC-MS, respectively. Results confirm that all the factors are significant and that must Zn and SO2 levels influence the presence of Strecker aldehydes in the final wine.

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