Zinc accumulation and utilization by wine yeasts

Abstract

Zinc accumulation and utilization by wine yeasts Raffaele De Nicola1,3, Nichola Hall2,3, Tatiana Bollag3, Georgios Thermogiannis3, Graeme M Walker31DSM Nutritional Products, Dept.NRD/CX, Basel, Switzerland; 2Vinquiry,Inc. Windsor, CA, USA; 3Schoolof Contemporary Sciences, Universityof Abertay Dundee, Dundee, UKAbstract: The present study has focused on the accumulation of zinc by wine yeast strainsof Saccharomyces cerevisiae during fermentation of both grape juice and chemically defi nedmedium with different carbohydrates and at varying levels of zinc. The results have shownthat zinc accumulation by wine yeast was very rapid with all zinc being removed from themedium by yeast cells within the fi rst two hours. Zinc uptake was stimulated by the presenceof sucrose. Zinc affected fermentation progress at defi ned levels, with optimal concentrationsat 1.5–2.5 ppm, depending on yeast strain and zinc bioavailability. The bioavailability of metalions in grape must and the roles of metals in wine yeast physiology are aspects poorly understoodby enologists. In brewing, it has long been recognized that malt wort may be zinc defi cient andbrewers often carry out zinc supplementations to avoid sluggish and incomplete fermentations.In winemaking, zinc levels in grape musts may be compromised depending on the bioavailabilityof zinc ions in vineyard soils as well as treatments with fertilizers and fungicides during grapegrowing. As a consequence, sub-optimal zinc levels in grape musts may negatively infl uence thefermentative performance of yeasts. We believe that optimization of metal ion bioavailabilitywill improve yeast fermentation performance in industrial processes and this study addressessome issues relating to zinc in enology.Keywords: zinc, metal ions, micronutrients, Saccharomyces cerevisiae, winemaking