Zinc accumulation and utilization by wine yeasts

Abstract:

The present study has focused on the accumulation of zinc by wine yeast strains of Saccharomyces cerevisiae during fermentation of both grape juice and chemically defi ned medium with different carbohydrates and at varying levels of zinc. The results have shown that zinc accumulation by wine yeast was very rapid with all zinc being removed from the medium by yeast cells within the fi rst two hours. Zinc uptake was stimulated by the presence of sucrose. Zinc affected fermentation progress at defi ned levels, with optimal concentrations at 1.5–2.5 ppm, depending on yeast strain and zinc bioavailability. The bioavailability of metal ions in grape must and the roles of metals in wine yeast physiology are aspects poorly understood by enologists. In brewing, it has long been recognized that malt wort may be zinc defi cient and brewers often carry out zinc supplementations to avoid sluggish and incomplete fermentations. In winemaking, zinc levels in grape musts may be compromised depending on the bioavailability of zinc ions in vineyard soils as well as treatments with fertilizers and fungicides during grape growing. As a consequence, sub-optimal zinc levels in grape musts may negatively infl uence the fermentative performance of yeasts. We believe that optimization of metal ion bioavailability will improve yeast fermentation performance in industrial processes and this study addresses some issues relating to zinc in enology.

Keywords::

• zinc
• metal ions
• micronutrients
• Saccharomyces cerevisiae
• winemaking