Wood blocks as a carrier for Saccharomyces Cerevisiae used in the production of ethanol and fructose

Abstract

Saccharomyces cerevisiae ATCC 39859 was immobilized onto small cubes of wood in order to produce very enriched fructose syrup from synthetic glucose-fructose mixtures, through the selective fermentation of glucose. The kinetics of growth and ethanol production rates were studied. Several tests to assess the influence of substrate and product concentration on the production rates were carried out and appropriate rate equations were proposed as a design basis for continuous immobilized reactors. The ethanol production rate and cell growth rate were found to be inhibited linearly by both substrate and product concentrations. A maximum ethanol productivity of 21.9 g 1 −1 h −1 was attained from a feed containing 10% (by weight) glucose and 10% (by weight) fructose. The ethanol concentration was 29.6 g 1 −1, the glucose conversion was 78% and a fructose yield of 99% was obtained. This resulted in a final fructose:glucose ratio of 2.7. At lower ethanol productivity levels the fructose:glucose ratio increased, as did the ethanol concentration in the effluent. The ethanol productivities obtained in this study were 33%–132% higher than those obtained in a previous study using the same system, under similar conditions, with the cells immobilized in alginate beads.