Charity Maosah*, Tom Collins and James Harbertson
*Washington State University, 1900 Stevens Dr., Apt 615, Richland, WA, 99354-2131 (charity.maosah@wsu.edu)

Every year, wine producing countries are affected by smoke from wildfires. Wine made from grapes that have been exposed to smoke from wildfires can have unpleasant burnt, leather, smoky, and other sensory attributes. Smoke-related volatile phenols that play a role in the smoky characteristics exist as free phenols and sugar-bound glycosides. Free volatile phenols contribute to smoky aromas in wine. After wine fermentation, acid-mediated hydrolysis can release bound phenols, leading to increased smoky aromas. To improve the quality of smoke-affected wines, both free and bound smoke-related phenols must be removed or reduced. There are no effective means to reduce both free and bound smoke phenols in affected wines. Use of reverse osmosis (RO) with solid phase adsorption reduces free-smoke related phenols but not bound-smoke related phenols. This can result in smoke recurrence after some time. This study evaluates the use of immobilized β-glucosidase to release bound-smoke related phenols in wine and permeate which can then be removed by RO and suitable adsorption technique. Smoke-affected wines were treated using RO to create a permeate containing the phenol glycosides. β-glucosidase was immobilized in cross-linked chitosan-silica microspheres. Both original wine and permeate were subjected to hydrolysis by immobilized β-glucosidase at different temperatures for four hours. Released volatile phenols can then be removed by adsorption using activated carbon. Enzyme hydrolysis of phenol-glycosides was dependent on sample type (wine or permeate), temperature, and incubation period. In both wine and permeate, 35°C had highest hydrolysis of phenol-glycosides (21.47% and 33.82%, respectively) with a high hydrolysis rate within the first two hours of incubation. This combination of immobilized enzyme with RO and adsorption can improve the quality of smoke-affected wines and greatly reduce losses incurred by grapegrowers in the case of wildfires.

Funding Support: USDA Washington State Wine Agricultural Research Service