title: Influence of yeast immobilization on fermentation and aldehyde reduction during the production of alcohol-free beer.
abstract: Production of alcohol-free beer by limited fermentation is optimally performed 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 aldehyde reduction was monitored. Immobilized cells showed higher activities of hexokinase and pyruvate decarboxylase compared to cells grown in batch culture. In addition, a higher glucose flux was observed, with enhanced excretion of main fermentation products, indicating a reduction in the flux of sugar used for biomass production. ADH activity was higher in immobilized cells compared to that in suspended cells. However, during prolonged production a decrease was observed in NAD-specific ADH activity, whereas NADP-specific activity increased in the immobilized cells. The shifts in enzyme activities and glucose flux correlate with a higher in vivo reduction capacity of the immobilized cells.
authors.affiliation: Department of Food Technology and Nutritional Sciences, Wageningen University, Wageningen, The Netherlands
authors.lastname: van Iersel MF
authors.initials: E
authors.lastname: Brouwer-Post
authors.initials: FM
authors.lastname: Rombouts
authors.initials: T
authors.lastname: Abee