The purpose of this investigation was to determinate effects of distillation cuts on the distributions of higher alcohols (1-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol, 2-methyl-1-butanol, 1-butanol, 2-butanol, 1-hexanol and 1-pentanol) and esters (ethyl acetate, isopentyl acetate + ethyl lactate, isobutyl acetate, ethyl propionate and ethyl butyrate) in plum brandy. The volatiles were determined by gas chromatography-flame ionization detection. The three most popular plum varieties used in plum brandy (Sljivovica) production, Stanley, Pozegaca and Bilska rana (Buhler), were distilled using a traditional distilling pot and fraction distillation. Three distillation cuts were considered. After separating the head fraction, in the amount of 1.7% of the distilling pot volume, heart fractions were cut at 40, 45 and 50% (v/v) ethanol and tail fractions, analogous to the heart fraction, were collected up to 10% (v/v) ethanol. The ratio of the content of 2-methyl-1-propanol and 3-methyl-1-butanol was 1:1 in the plum brandy produced from Stanley and Pozegaca and the ratio was 2:1 in the plum brandy produced from Bilska rana. This ratio can be used as a 'mark' of variety recognition in plum brandy production. The main differences in the heart fraction were accounted for by the content of the higher alcohols and esters for the distilling cut at 40 and 50% (v/v) ethanol.

Fermentations with yeast Saccharomyces cerevisiae in semiaerobic and in static conditions with the addition of chromic chloride into the used molasses medium were analysed. It was proved that the addition of optimal amounts of CrCl3 into the basal medium enhanced the kinetics of alcohol fermentations. The addition of 200 mg/l CrCl3 into the medium stimulated both the yeast growth and the ethanol production in all experimental conditions. On the other hand, the results showed that Cr3+ ions were incorporated into yeast cells during fermentation. Under these conditions the accumulation of Cr3+ ions was performed by yeast cells during the exponential growth phase, and with enriched amounts of 30-45 microg/g(d.m) of cells. Yeast biomass enriched with chromium ions was extracted with 0.1 mol/l NH4OH assuming that the extracts had the glucose tolerance factor (GTF). Then the extracts were passed through a gel-filtration column in order to isolate and purify the GTF. The presence of GTF in the purified fractions was determined by measuring the absorbance at 260 nm. It is evident from the obtained results that the added purified fractions enhanced the rates of CO2 production as well as the glucose utilization during alcoholic fermentation. As expected, the enhancement of both rates depended on the amounts of extracts added to the fermentation substrate. Thus, it is evident that purified extracts contained the GTF compound, and that Cr3+ ions were bonded to the protein molecule.

No abstract

Summary. More glycogen and trehalose is formed in aerobically incubated baker's yeast than under anaerobic conditions, glucose being a more favourable source of sugar than maltose. The regulation of tBe formation of glycogen in aerobic incubations of non-proliferating baker's yeast in the presence of glucose can be explained by the action of the activators and inactivators (Rothman & Cabib, 1967). The level of ATP in the cell does not affect the formation of trehalose in the same way as it influences the formation of glycogen.The incubation temperature chosen can be used to manipulate the relative proportions of glycogen and trehalose in baker's yeast. 30~ is the optimum for the formation of glycogen, and at 45~ none at all is formed. The inhibition of the biosynthesis of glycogen is not, at least primarily, a consequence of the effect of the elevated temperature on the enzymes taking part in the formation of glycogen. The optimum temperature for the formation of trehalose is 45~ and at this temperature baker's yeast containing as much as 20% trehalose can be obtained.

Procedures for the production of Saccharomyces cerevisiae biomass enriched with iron and the effects of the iron ions addition into the molasses medium on the yeast growth and the production of ethanol were studied. The growth of the yeast S. cerevisiae and the ethanol production in media with different concentrations of Fe were monitored in the batch process under semiaerobic and anaerobic conditions. The highest biomass concentration and ethanol production were achieved in the medium with 0.6-0.8 g l -1 of Fe under both (semiaerobic and anaerobic) conditions. Kinetics of the iron ions accumulation in yeast cells during 24 h of growth in the batch process under semiaerobic and anaerobic conditions were monitored. In anaerobic conditions the maximum uptake (10 mg g -1 d.m. yeast biomass) was obtained after 12 h of fermentation, while in semiaerobic conditions a four times lower uptake (2.5 mg g -1 d.m. yeast biomass) was obtained after 16 h of fermentation.