PRODUCTION OF ZINC-ENRICHED BIOMASS OF SACCHAROMYCES CEREVISIAE

Zinc accumulation and the growth of Saccharomyces cerevisiae were investigated in a culture with zinc sulfate-supplemented medium. The cultivations were performed on Sabouraud dextrose broth medium in aerobic conditions, without the addition of zinc (control culture) and with the addition of zinc sulfate (5, 10, 15, 30 and 60 mg ZnSO4 l(-1) medium) at 28 degrees C for 72 hours. The results showed similar trends of yeast growth rates at 24, 48, and 72-hour interval, with concentrations above 10 mg l(-1) ZnSO4 in the nutritional medium significantly decreasing the yeast growth rate and the biomass yield (P<0.05). Substantial differences between the initial ZnSO4 concentrations in the growth medium were demonstrated in the overall adsorption of Zn ions (Zn2+) in yeast cells by a colorimetric assay (P<0.05). Similarly, the content of total accumulated zinc, as well as the fractions of Zn present in cells depended mainly on the zinc concentration in the medium, as the total Zn accumulation and organically bound Zn fractions were increased by elevating the ZnSO4 supplementation in the culture medium up to 30 mg l(-1) but gradually reduced by any further addition of ZnSO4 determined by an ICP-MASS assay (P<0.05). In the presence of 30 mg l(-1) ZnSO4, the Zn content in the biomass increased by 24-fold, to 4132.34 mu g g(-1) in comparison to 171.9 mu g g(-1) achieved in the basal medium. Thus, the ability of S. cerevisiae to accumulate zinc can be used for production of a zinc-rich ingredient for functional food products.