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

TLDR

The study examined the impact of drying temperatures (60, 100, and 140 °C) on polyphenol content and antioxidant activity in red grape pomace peels. Freeze‑dried peels served as reference, and the authors measured CIE‑LAB color, total extractable polyphenols, condensed tannins, UV‑vis spectra, and antioxidant activity. Drying at 100 °C and 140 °C reduced total polyphenols by 18.6 % and 32.6 %, condensed tannins by 11.1 % and 16.6 %, and antioxidant activity by 28 % and 50 %, while 140 °C also increased hue angle, color difference, and caused red color loss; 60 °C had no significant effect. Keywords: wine byproducts; grape pomace peels; antioxidant activity; drying temperature.

Abstract

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