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 hot-air,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.