MODELING OF CONTINUOUS CORN STARCH HYDROLYSATE FERMENTATIONS IN IMMOBILIZED-CELL REACTORS

Corn starch hydrolysate has been fermented by two different strains of Saccharomyces cerevisiae and SaccharomyCes oviformis, either in batch or in continuous modes, using both suspended-cell and entrapped-cell systems, provided with different porous supports, namely a commercial synthetic sponge, crushed almond skins and alginate beads. The present results demonstrate that starch hydrolysate is an excellent substrate for alcohol fermentation, whether out of the presence of growth factors for the yeast or in absence of inhibiting substances. A semi-empirical kinetic model, previously proposed for comparing the results of continuous fermentations of various substrates in different reactors, is now successfully extended to the study of different porous supports for cell entrapment in a fixed-bed column. The best results in terms of ethanol productivity (7.8 g(p)/1h, referred to the whole reactor volume) are obtained entrapping the yeast cells within the spongy matrix.