Influence of yeast immobilization on fermentation and aldehyde reduction during the production of alcohol-free beer

Production of alcohol-free beer by limited fermentation is optimally perfor med in a packed-bed reactor. This highly controllable system combines short contact times between yeast and wort with the reduction of off-flavors to concentrations below threshold values. In the present study, the influence of immobilization of yeast to DEAE-cellulose on sugar fermentation and alde hyde reduction was monitored. Immobilized cells showed higher activities of hexokinase and pyruvate decarboxylase compared to cells grown in batch cul ture. In addition, a higher glucose Bur was observed, with enhanced excreti on of main fermentation products, indicating a reduction in the flux of sug ar used for biomass production. ADH activity was higher in immobilized cell s compared to that in suspended cells. However, during prolonged production a decrease was observed in NAD-specific ADH activity, whereas NADP-specifi c activity increased in the immobilized cells. The shifts in enzyme activit ies and glucose flux correlate with a higher in vivo reduction capacity of the immobilized cells. (C) 2000 Elsevier Science Inc. All rights reserved.