Continuous production of very enriched fructose syrup by the conversion of glucose to ethanol from glucose-fructose mixtures in an immobilized cell reactor

The yeast Saccharomyces cerevisiae ATCC 36859, which preferentially utilizes glucose in glucose-fructose mixtures, was immobilized and used for the continuous production of very enriched fructose syrup. A syrup containing fructose as 99% of the reducing sugars was produced from a 10.1% w/v glucose and 9.8% w/v fructose mixture at a dilution rate of 0.106 h⁻¹. Later in this process when the dilution rate was increased to 0.366 h⁻¹ the ethanol productivity was 12.7 g 1⁻¹ h⁻¹. This is 16% less than the value attained in a similar medium containing only glucose as the carbohydrate. The fructose content was also increased from 55 to 95% of the reducing sugars in a food grade mixture of high fructose corn syrup and Jerusalem artichoke juice. Purification of the product with activated carbon and ion-exchange resin produced a stable, colourless and very enriched fructose syrup suitable for human consumption.