DIFFUSION OF SUGARS AND ALCOHOLS THROUGH COMPOSITE MEMBRANE STRUCTURES IMMOBILIZING VIABLE YEAST-CELLS

This paper investigates the diffusivity of sugars (glucose and xylose) and alcohols (ethanol and xylitol) in a composite immobilized-cell st ructure that consists of a flat agar layer encompassed between two mic roporous membrane filters. Viable cells of glucose- and xylose-ferment ing yeasts (i.e., Saccharomyces cerevisiae and Candida shehatae, respe ctively) were entrapped in the gel layer. The diffusional resistance o f the composite structure to nonmetabolizable solutes (L-sugar isomers and alcohols) was measured before and after incubation in a two-chamb ered bioreactor with asymmetrical feeding of the immobilized cell laye r. One chamber of the bioreactor was filled with a mixture of glucose and xylose, and the other chamber with a substrate-free medium. (C) 19 98 Elsevier Science Inc.