Zeinab Mohammadi Shad, Emily Kuelbs, Chandrasekar Venkitasamy, Lucas Buren, and Aude Watrelot*
*Department of Food Science and Human Nutrition, Iowa State University, 536 Farm House Lane, 2567 Food Sciences Building, Ames, IA 50011 (watrelot@iastate.edu)

The winemaking process produces ~20% of the weight of the fresh grapes as grape pomace, a solid by-product composed of skins, seeds and some part of stems and rice husks. This by-product is rarely re-used in winemaking in spite of its polyphenol content and biological properties. The goal of this study was to optimize a sustainable drying method for cold-hardy grape pomace to make a microbiologically safe powder that contains polyphenols with antioxidant properties. Two drying methods, hot air (HA) and catalytic infrared (IR) heating using three temperatures, were applied to Edelweiss and Marquette pomaces. The moisture content of the pomaces was evaluated prior to chemical analysis. The color was evaluated using a chromameter (Hunter Lab ColorFlex EZ), the phenolic compounds were extracted using 70% acidified acetone, and the total iron-reactive phenolic compounds content in the extracts was measured. The initial moisture content of grape pomace ranged from 50 to 70% (wet basis) and was reduced to a moisture content of <10% by IR heating for 30 min, while HA drying took ~3 hr. Edelweiss white pomace dried by IR was significantly darker, with lower L* and b* values than when dried by HA. The color of Marquette pomaces was not affected by drying method. Between 10 to 13% of polyphenols were extracted from the dry and ground pomaces. No effect of drying method was observed on the phenolic compounds and condensed tannin content of Edelweiss pomace extracts. The antioxidant activity of pomace extracts will be measured using the DPPH free radical assay to determine the effect of IR drying on the biological properties of grape pomace and to valorize this by-product.

Funding Support: USDA-AMS Iowa Department of Agriculture and Land Stewardship Specialty Crop Block Grant Program