TOTAL POLYPHENOLS AND ANTIOXIDANT ACTIVITY IN SWEET POTATOES (IPOMOEA BATATAS L.) AFTER HEAT TREATMENT

Abstract

Sweet potatoes are reported to be a good source of bioactive compounds. The aim of this study was to evaluate the impact of different heat treatment methods (microwaving, steaming, and baking) and variety on the total polyphenol content and antioxidant activity of three sweet potato varieties – Beauregard (orange-fleshed), O’Henry (white-fleshed), and 414-purple (purple-fleshed). All investigated parameters were determined spectrophotometrically. The total polyphenol content was in the range of 0.53 (O’Henry) – 5.60 mg GAE.g^-1 DW (414-purple) for raw flesh and 1.68 (O’Henry) – 7.03 mg GAE.g^-1 DW (414-purple) for raw peel of sweet potatoes. Heat treatments caused an increase of total polyphenol content in sweet potatoes (0.98 (steamed O’Henry) – 28.04 mg GAE.g^-1 DW (baked 414-purple)). In terms of antioxidant activity, the steamed samples of variety 414-purple showed the highest values of DPPH radical scavenging activity (4.51 µmol TE.g^-1 DW) and Ferric reducing antioxidant power assay (19.57 µmol TE.g^-1 DW) compared to the other treatment methods. Spearman´s test showed a strong positive relationship between both used methods for evaluation of antioxidant activity. All studied processing methods positively affected the total polyphenol content and antioxidant activity in sweet potatoes.