Enhancement of 2-phenylethanol productivity by Saccharomyces cerevisiae in two-phase fed-batch fermentations using solvent immobilization

The bioconversion of L-phenylalanine to 2-phenylethanol by Saccharomyces cerevisiae in fed-batch expts. has shown that concns. of 2-phenylethanol of >2.9 g/L have a neg. impact on the oxidative capacity of the yeast. Without tight control on ethanol prodn., and hence on the feed rate, ethanol rapidly accumulates in the culture media, resulting in complete inhibition of cell growth before the maximal 2-phenylethanol concn. of 3.8 g/L, obtained in the absence of ethanol prodn., could be achieved. This effect was attributed to a cumulative effect of ethanol and 2-phenylethanol, which reduced the tolerance of the cells for these two products. To enhance the productivity of the bioconversion, a novel in situ product recovery strategy, based on the entrapment of an org. solvent (dibutylsebacate) into a polymeric matrix of polyethylene to form a highly absorbent and chem. and mech. stable composite resin, was developed. Immobilization of the org. solvent successfully prevented phase toxicity of the solvent and allowed for an efficient removal of 2-phenylethanol from the bioreactor without the need for prior cell sepn. The use of the composite resin increased the volumetric productivity of 2-phenylethanol by a factor 2 and significantly facilitated downstream processing, because no stable emulsion was formed. The 2-phenylethanol could be backextd. from the composite resin, yielding a concd. and almost cell-free soln. In comparison to two-phase extractive fermns. with cells immobilized in alginate-reinforced chitosan beads, the use of a composite resin was extremely inexpensive and simple. In addn., the composite resin was insensitive to abrasion and chem. stable, such that sterilization with 2M NaOH or heat was possible. Finally, the composite resin could be produced on a large scale using com. available equipment. [on SciFinder (R)]