Effect of pretreatments and drying temperatures on sweet potato flour


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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.