yeast-catalysed conversion of ethanol to acetaldehyde. The coupled-substrate reaction in
solid/gas system is illustrated in Figure 9.9.
As described previously, the same behaviour was observed with lipolytic enzymes
regarding the dependence of stability and enzymatic activity on the hydration level of the
system. As indicated on Figure 9.10, alcohol dehydrogenase was responsible for the
conversion of hexanal to hexanol and the cofactor regeneration was effective. In this
experiment, 200 mg of baker’s yeast was placed at 65°C in the solid/gas bioreactor
depicted in Figure 9.3. The total flow passing into the bioreactor was 680 μmoles/min.
The hexanal activity was fixed at 0.05 (5 μmoles/min), the ethanol activity at 0.1 (73
μmoles/min), and
Figure 9.9 Model for hexanal
reduction by YADH of baker’s yeast
with an NAD
+regenerating system
with ethanol.
Solid/gas systems, theory and applications 277