VIEW ARTICLE    DOI: 10.1094/ASBCJ-52-0100

Wort Aldehyde Reduction Potential in Free and Immobilized Yeast Systems. A. Debourg, M. Laurent, E. Goossens, E. Borremans, L. Van De Winkel, and C. A. Masschelein, CERIA Institut des Industries de Fermentation, 1 Avenue E, Gryson, B-1070 Brussels, Belgium. J. Am. Soc. Brew. Chem. 52:0100, 1994.

Previous works have shown that a wide range of carbonyl compounds are reduced during fermentation. However, recent studies indicated that aldehyde-reducing systems may be more complex than has been previously assumed. The present work investigated process parameters that may affect the removal of wort carbonyls in free and immobilized yeast systems. In vivo measurements have shown that the relationship between the carbonyl structure and the reduction rate was the same in free and immobilized yeast. Nevertheless, experiments with permeabilized yeast cells suggested that membrane permeability is not a major limiting factor in achieving subthreshold carbonyl levels. The comparison of in vivo aldehyde reduction rates in a haploid adh-0 mutant and in an adh-0 strain subsequently transformed with an ADH1, ADH2, or ADH3 gene showed that ADH1 is only one of the enzymes involved in the reduction of carbonyl compounds. Data collected in vitro also showed a considerable heterogeneity in the enzymatic systems involved in the reduction of carbonyl compounds in yeast. Results further indicate that an immobilized yeast fermentation process, at low temperature and high residence time, seems to offer the best compromise between low alcohol content and subthreshold carbonyl levels.

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