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The aim of the present work was to study the incorporation of some microelements in the yeast S. cerevisiae and its impact on the physiological state of the yeast cells during the alkoholic fermentation. The cultivations were performed on molasses medium in anaerobic and semiaerobic conditions with and without the addition of zinc, copper and manganese sulphate (0.1 g/L of each) at 30oC and different pH values of the medium (3.5-6) for 8 h. The addition of the mentioned salts in molasses medium enhanced the yield of the yeast biomass up to 30% in semiaerobic conditions, but the ethanol yield was changed very little. On the other hand, in anaerobic conditions, the yields of the yeast biomass were increased up to 10% and alcohol yield up to 20%. The highest amount of Zn ions in dry matter (0.7mg/g) was incorporated in the yeast biomass under anaerobic conditions. In contrast, the incorporation of Cu and Mn was preferred in semiaerobic conditions and the highest value of Cu ions in dry matter (1.1mg/g) and Mn in dry matter (0.3 mg/g) in yeast biomass were obtained. Optimal pH for all incorporations was between 4 and 5.

Procedures for the production of Saccharomyces cerevisiae TVG_4 biomass enriched in zinc and effects of zinc ions additions in the molasses meduim on yeast growth and production of ethanol were studied. The growth of S. Cerevisiae TVG_4 and ethanol production in media with different concentrations of zinc-sulphate were folowed in batch process under semiaerobic and anaerobic conditions. The highest biomass concentration was achieved in medium with 0.15 and 0.20 g L^-1 of zinc-sulphate, while the addition of 0,25 g L^-1 of zinc-sulphate was optimal for ethanol production under both ( semiaerobic and anaerobic ) conditions. Kinetics of zinc ions accumulation an yeast cells during 24 hours of growth in fed-batch process and in batch processes under semiaerobic and anaerobic conditions were also investigated. In all experiments, the accumulation of zinc ions was completed during the first 12 hours of cultivation. When semiaerobic conditions were applied, the concentration of zinc ions was about 0.25 mg g^-1, whereas in the case of anaerobic condition accumulation was 0.4 mg_Zn ˇ g^-1_d.m. of yeast cells. The higest concentration of zinc ions in yeast biomass ( 0.62 mg_Znˇ g^-1 ) was obtained in fed-batch cultivation.