Effect of carbohydrate substrate on fermentation by kefir yeast supported on delignified cellulosic materials

The suitability of delignified cellulosic (DC) material supported kefir yea st to ferment raw materials that contain various single carbohydrates, for the production of potable alcohol and alcoholic drinks, is examined in this investigation. Results are reported of fermentations carried out with sucr ose, fructose, and glucose in synthetic media. Repeated batch fermentations at various initial sugar concentrations of sucrose, fructose, and glucose were performed at 30 degreesC in the presence of the aforementioned biocata lyst. The results clearly show feasible yields in the range of 0.38-0.41 g/ g, alcohol concentrations of 7.6-8.2% v/v, fermentation time of 90-115 h, a nd conversion of 92-96%. DC material supported kefir fermented Ii-fold more rapidly than free cells and 9-fold more rapidly in comparison to kissiris supported kefir. The main volatile byproducts such as amyl alcohols (mixtur e of a-methyl-l-butanol and S-methyl-l-butanol), ethanal, and ethyl acetate were formed in all sugar fermentation products. The formation of 65-110 pp m of ethyl acetate is as high and even higher than that obtained with tradi tional wine yeasts. The increase of the initial concentration of sugar in t he fermentation media resulted in an increase in contents of volatiles. The fine aroma that was obtained in the product of fructose could be attribute d to the high percentage of ethyl acetate on total volatiles. The efficienc y of DC material supported kefir was the same for the fermentations of indi vidual sugars or a mixture of fructose, sucrose, and glucose. When whey wit h raisin extracts was fermented, lower yields were obtained but the aroma o f the product was even better.