Inhibition aspects of the bioconversion of l-phenylalanine to 2-phenylethanol by Saccharomyces cerevisiae

The inhibitory impacts of the bioconversion of l-phenylalanine (l-Phe) to 2-phenylethanol (PEA), a very important natural aroma compound, on the metabolism of Saccharomyces cerevisiae Giv 2009 were investigated in batch and chemostat cultures. The bioconversion was found to be completely growth associated and lead to a maximal final PEA concentration of 3.8 g/l of PEA. This was attained in a fed-batch procedure on glucose in order to prevent the formation of ethanol, which generally reduced the final achievable PEA concentration by its synergistic inhibitory effect. Chemostat cultures revealed that the bioconversion uncoupled the catabolism from anabolism of S. cerevisiae especially under oxidative growth conditions and thereby reduced the critical dilution rate Dcrit. In addition, higher specific oxygen uptake rates qO2 were found in the presence of the bioconversion at oxidative growth than the maximal respiratory capacity qO2max found in continuous cultures without bioconversion.