Effect of drying temperatures on properties of sweet potato flour

Abstract

VitAto is an orange-fleshed sweet potato variety introduced by the Malaysian Agricultural Research and Development Institute (MARDI) in 2017. Due to the susceptibility of fresh sweet potatoes to deterioration during storage, they are frequently processed into flour. The drying process is crucial in preserving the quality of flour. Thus, this study investigated the impact of oven drying at three different temperatures (50, 70 and 90°C) on the physical and functional properties of VitAto sweet potato flour. The range of values for physical properties of VitAto flour were: moisture (2.09 to 6.59%), water activity (0.38 to 0.40), pH (5.79 to 6.38), bulk density (0.22 to 0.25 g/ml), and tapped density (6.94 to 7.21 g/ml). Flour dried at 50°C best preserved the orange colour (L∗=84.45±0.33; a∗=16.64±0.19; b∗=25.65±0.42), whereas flour dried at 90°C exhibited a yellowish colour (L∗=89.56±0.32; a∗=2.99±0.06; b∗=32.45±0.10). Increasing the drying temperature led to a gradual increase in water absorption capacity, wettability, and swelling power, but oil absorption capacity decreased. The results of the pasting profile indicated significant variations in viscosity properties due to drying temperatures. Flour dried at 50°C had the lowest peak viscosity (393.67 mPa.S), breakdown viscosity (219.33 mPa.S), setback viscosity (59.33 mPa.S) and final viscosity (233.67 mPa.S). In conclusion, the drying temperatures distinctly influenced the quality characteristics of VitAto sweet potato flours, thereby altering their functionality.