Optimization of hot-air drying conditions on functional properties of flour from dried South African sweet potato cultivars (Impilo and Bophelo) using the response surface methodology

Abstract The response surface method (RSM) has an important application in formulation of new products. This study determined the effect of electric hot-air drying on the functional properties of flour made from orange-fleshed sweet potato (OFSP). Flour from the cultivars Bophelo (B) and Impilo (IM) were treated with 13 temperature-time combinations designed by STAT EASE software version 8.01.0. Bophelo flour dried at 70 °C for 8.6 hrs and Impilo at 70 °C for 14.4 hrs showed the lowest gelatinization temperatures and enthalpy of gelatinization (ΔH), indicating ease of cooking. The highest swelling power of 12.45 g/g for Bophelo and 8.16 g/g for Impilo were significantly higher than the remaining samples. Flours for Bophelo and Impilo at drying temperatures and times at 70 °C for 4.4 hrs, 56 °C for 6.5 hrs and 60 °C for 6.5 hrs indicated favourable gelling properties and cost of drying, implying that these can be used at household level and in food industries as thickeners from both cultivars.