Effects of Drying Processes on the Antioxidant Properties in Sweet Potatoes

The effects of different drying methods (hot-air drying, microwave drying and vacuum-freeze drying) on the antioxidant activity and antioxidants in sweet potato (Ipomoea batatas L. Lam.) tubers were investigated to determine the potential drying process. Sweet potato tubers were cut into 5 mm thick slices, steamed at 100°C for 10 min, then dried in either hotair, microwave, or vacuum-freeze. The dried sweet potatoes in microwave possessed the highest antioxidant activity, while the lowest activity was observed in hot-air dried samples. The phenolic contents were positively correlated with scavenging activity and reducing power of DPPH+. The microwave drying retains the highest antioxidant activity with the highest content of phenolic compounds in dried sweet potatoes. β-carotene and ascorbic acid showed minor contribution to the antioxidant activity in dried sweet potatoes.