from S. cerevisiae [12]. To determine its contribution to the
reduction of wort aldehydes, cell extracts were separated on
IEF gels, and reducing activity was analyzed using an activity
stain with the coenzymes NADH or NADPH (Fig. 4).
With NADPH, reductase activity in the anaerobic CE was
detected with hexanal and 3-methylbutanal, residing at a pI
of 5.9. With NADH, a large activity spot was observed in
the CE lane with hexanal, indicating that additional enzymes
were able to reduce this compound. On the other
hand, with 3-methylbutanal, reductase activity in the presence
of NADH resided in a distinct spot at pI 5.9, similar to
the activity with NADPH.
In addition, in vitro NADP-reducing activity was determined
in yeast cell extracts during the production of alcohol-
free beer. In contrast to NAD-specific ADH, the NADPspecific
activity increased from approx. 0.05 to 0.1 U/mg
protein over a 70 day production period (Fig. 5). Activity in
the immobilized cells was also significantly higher when
compared to cells that were grown in aerobic or anaerobic
batch cultures, which had activities of 0.010 and 0.019
U/mg protein, respectively.