Growth of Candida utilis on a mixture of monosaccharides, acetic acid and ethanol as a model of waste sulphite liquor.

Candida utilis cultivated under batch conditions in a synthetic medium with a mixture of different carbon sources utilized first D-glucose and then D-galactose, D-mannose, D-xylose, L-arabinose, ethanol and acetic acid. The effect of acetic acid was primarily a function of pH and the physiological state of the inoculum. At pH 4.5, acetic acid at a concentration of 1 g/l increased the specific growth rate, reduced time of cultivation and increased yield of the yeast dry weight. The yield from acetic acid was 61%. In the presence of a higher content of acetic acid (3--6 g/l) the yield was only 18--26%. The yield calculated only from monosaccharides increased but the yield with respect to total carbon sources was lower. The specific growth rate decreased as well. The addition of ethanol also resulted in an increase of the production and yield of the yeast dry weight but the cultivation time was prolonged. The simultaneous utilization of carbon sources of the studied mixture modelling a sulphite fermentation medium with ethanol is advantageous. However, due to physiology of the yeast, it is most suitable to cultivate a strain adapted to utilizable carbon sources in a continuous way, in the presence of their limiting concentrations in the cultivation medium.