Effects of steaming and drying on quality and antioxidant activity of white-fleshed sweet potato powder (Ipomoea batatas)

Abstract

White-fleshed sweet potatoes (WFSP) are rich sources of polyphenols. The flesh of PFSP contains total polyphenol content (TPC) at 1.52 mgGAE/g fresh weight. The raw material’s total free radical scavenging capacity was estimated (at 42.4% DPPH). The inactivation of peroxidase (POD) and polyphenol oxidase (PPO), the breakdown of total phenolic compounds, antioxidant activity, and the whiteness of WFSP were evaluated during steam blanching from 0 to 9 minutes. Steam blanching time from 7 to 9 minutes at boiling temperature (100ºC) inactivated most of the POD and PPO enzymes (71.2% and 70.5%, respectively), thus TPC and antioxidant activity remains high, resulting in a bright white product. After 7 minutes of blanching, drying experiments of WFSP slices were conducted at air temperatures of 50 to 80ºC. The best alternative for describing and understanding the drying of WFSP slices was the Page model. In the temperature’s ranges, the values of the moisture diffusivity (De f f) and activation energy are obtained from 3.059×10−12 to 5.095×10−12 m2 /s and 14.93 kJ/mol, respectively. The drying temperature of 70ºC for 10 hours was suitable for producing WFSP powder with low water activity (0.5) and moisture content (6.5%), high TPC and antioxidant activity, and low specific energy consumption. These results suggested that the WFSP powder exhibited potential as a nutraceutical ingredient product.