Optimising glucose conversion in the production of reduced alcohol wine using glucose oxidase

The use of a glucose oxidase (GOX)-catalase enzyme system for the production of reduced-alcohol white wine is investigated. The process reduces alcohol potential by converting glucose to gluconic acid. Trials were conducted with grape juice and model solution to determine key factors affecting the activity of the GOX system, and to optimise the process for use with grape juice. Under our processing conditions, the low pH of grape juice was found to be a dominant limiting factor in the rate and extent of glucose conversion by GOX. An optimised process for glucose conversion (up to 87%) was developed after investigation of the effects of enzyme dosage, sparging, aeration and mixing rates, and temperature. Maximum GOX activity was observed during the first 4 to 6 h of treatment, after which a significant decrease in the rate of gluconic acid formation and glucose degradation occurred. An expected increase in titratable acidity and concurrent decrease in pH during GOX treatment was also observed, and is attributable to an increase in the juice gluconic acid concentration of ca 73 g/l.