The combined effect of time and temperature during oven drying on red grape pomace polyphenols, pigments, and antioxidant properties

This study had as a goal to carry out the drying of red grape pomace (RGP) using a 2 × 3 factorial design. The design of the experiment included combinations of time and temperature in order to achieve the lowest possible moisture levels and examine losses in precious polyphenols, but also the effect on the antioxidant properties of RGP extracts. Drying for 6 hrs at 80°C (D6/80) provided RGP with a satisfactory moisture level (11%). A comparison with untreated (fresh) RGP revealed that drying significantly decreases the polyphenol and anthocyanin pigments’ content. This decline was accompanied by a decrease in both the ferric-reducing power and antiradical activity of the RGP extracts. Although necessary for long-term RGP stability, drying should be implemented with caution because improper drying may have severe effects on the polyphenolic composition and antioxidant activity.