Peeling, drying temperatures, and sulphite-treatment affect physicochemical properties and nutritional quality of sweet potato flour

The effects of peeling, drying temperature (55–65 °C) and pretreatment on the physicochemical properties and nutritional quality of sweet potato flour were investigated. The flours were prepared from peeled and unpeeled sweet potatoes dipped in 0.5% sodium hydrogen sulphite (NaHSO3). There were significant differences (p < 0.05) in ΔE values and browning index between flours from peeled and unpeeled sweet potatoes without sulphite-treatment (PF and UF). On the other hand, flours from peeled and unpeeled sweet potatoes with sulphite-treatment (PSF and USF) had higher L∗, a∗, and b∗ values, swelling capacity, ascorbic acid, and total phenolics than PF and UF. However, USF and UF had higher β-carotene content than PSF and PF. β-Carotene and ascorbic acid contents decreased with increasing drying temperature for all flours, whereas total phenolics increased for PSF and USF. Therefore, the best quality product was obtained when samples were pretreated with sulphite before drying at any temperature.