Physical and Functional Properties of Sweet Potato Flour: Influence of Variety and Drying Method

Sweet potato (<i>Ipomoea batatas</i> (L.) Lam.; SP) flour enhances food nutrition and bioactivity while functioning as a thickening/gelling agent. This study investigated the impact of two drying methods [hot-air (75 °C/20 h) and freeze-drying (-41-30 °C/70 h)] on the physical-functional properties of flours from three SP varieties: <i>Bonita</i> (white-fleshed), <i>Bellevue</i> (orange-fleshed), and <i>NP1648</i> (purple-fleshed). Particle size, morphology, water/oil absorption capacities (WAC/OAC), bulk density, swelling power (SwP), water solubility (WS), foaming/emulsifying properties, least gelation concentration (LGC), and gelatinisation temperature (GT) were analysed. Both the drying method and variety significantly influenced these properties. Hot-air-dried flours exhibited bimodal particle distribution, compact microstructure, and aggregated starch granules, yielding higher WAC (≈3.2 g/g) and SwP (≈3.6 g/g). Freeze-dried flours displayed smaller particles, porous microstructure, and fragmented granules, enhancing OAC (≈3.0 g/g) and foaming capacity (≈17.6%). GT was mainly variety-dependent, increasing as <i>Bellevue</i> (74.3 °C) < <i>NP1648</i> (78.5 °C) < <i>Bonita</i> (82.8 °C), all exceeding commercial potato starch (68.7 °C). <i>NP1648</i> required lower LGC (10% vs. 16% for others). All flours exhibited high WS (24-39.5%) and emulsifying capacity (≈44%). These results underscore the importance of selecting the appropriate drying method and variety to optimise SP flour functionality for targeted food applications. Freeze-dried flours might suit aerated/oil-retentive products, while hot-air-dried flours could be ideal for moisture-sensitive formulations.