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The aim of the present work was to study the incorporation of some microelements in the yeast Saccharomyces cerevisiae and its impact on the physiological state of the yeast cells during the alcoholic fermentation. The cultivations were performed on molasses medium in anaerobic (thermostat) and semiaerobic (shaker) conditions, with and without the addition of zinc, copper and manganese sulphate (0.1 g/L of each) at 30 °C and different pH values of the medium (3.5–6.0) 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 %. After the fermentations were performed, the concentration of metal ions in yeast cells was determined. Different values were achieved depending on the used growth conditions. The highest amount of Zn ions in dry matter (700 μg/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 Cu2+ ions in dry matter (1100 μg/g) and Mn2+ in dry matter (300 μg/g) in yeast biomass were obtained. Optimal pH for all ion incorporations was between 4 and 5.

The influence of the lactose content in the medium and of the air flow rate on the biomass yield of the yeast Kluyveromyces marxianus on whey substrate was investigated. For this purpose, batch processes were conducted in a laboratory bioreactor (2L) with the yeast Kluyveromyces marxianus ZIM75 in media with different contents of lactose and at different air flow rates. The higest biomass yield (5,9 g d.m./L) was achieved at the highest air flow rate (1,5 L/L min) in the medium with 10% of lactose. The specific growth rate increased with increased air flow rate, and the highest specific growth rate of 0,1060 h-1 was achieved at the highest air flow rate in the medium with 5% of lactose. However, the best conversion of lactose carbon to biomass (0,104 g/g) was achieved in the medium with 5% of lactose.

The conditions of lactose hydrolysis with enzyme preparation of D-galactosidase were investigated. The aim of this work was to considered the use of whey in fermentative processes with yeast Saccharomyces cerevisiae. Enzymatic hydrolysis was conducted at different temperatures, with different lactose concentrations in medium and different concentrations of added enzyme. The results show that optimal temperature for hydrolysis was 40°C. The optimal amount of enzyme preparation was 2 gL-1 in lactose medium with 5-10 % lactose.