Effect of pretreatments and drying temperatures on sweet potato flour

Effect of pretreatments with 1 w/v% sodium hydrogen sulphite (NaHSO₃) and 1 w/v% calcium chloride (CaCl₂) and drying temperatures (55, 60 and 65 °C) on sweet potato flour were investigated. Flour treated with CaCl₂ had higher amounts of ascorbic acid and β‐carotene (10.61–12.54 and 3.26–3.46 mg 100 g^?1 wet basis, respectively) than that treated with NaHSO₃ (9.47–11.47 and 3.05–3.43 mg 100 g^?1 wet basis, respectively). Total phenolic content and water absorption index (wet basis) were highest at 65 °C when treated with NaHSO₃ (10.44 mg 100 g^?1 and 2.49 g g^?1 respectively) and CaCl₂ (9.52 mg 100 g^?1 and 2.85 g g^?1 respectively). Swelling capacity (wet basis) was highest at 60 °C when treated with CaCl₂ (2.96 g g^?1) whereas when treated with NaHSO₃ (2.85 g g^?1) it was highest at 55 °C. Freeze‐dried samples treated with NaHSO₃ had higher lightness and total phenolic content while CaCl₂‐treated samples had higher β‐carotene and ascorbic acid. The results showed that good quality flour could be produced after soaking in CaCl₂ and dried at 65 °C.