Effect of Drying Temperature on the Stability of Polyphenols and Antioxidant Activity of Red Grape Pomace Peels

The effect of drying temperature (60, 100, and 140 °C) on the polyphenols' content and antioxidant activity of red grape pomace peels was studied. Freeze-dried samples were used as reference. Differences on the CIE-LAB color, total extractable polyphenols, condensed tannins, UV−vis spectra, and antioxidant activity were evaluated. When drying temperature was 100 and 140 °C, a significant reduction in both total extractable polyphenols (18.6 and 32.6%) and condensed tannins (11.1 and 16.6%) was observed, as well as a decrease of 28 and 50% in the antioxidant activity of the samples, respectively. Hue angle and total color difference in the sample dried at 140 °C were significantly higher than in the freeze-dried reference material. A red color loss at 140 °C was also confirmed by lower absorbance values in the spectra at 525 nm. Drying at 60 °C did not significantly affect the sample characteristics evaluated. Keywords: Wine byproducts; grape pomace peels; antioxidant activity; drying temperature