Effects of Steaming and Dehydration on Anthocyanins, Antioxidant Activity,Total Phenols and Color Characteristics of Purple-Fleshed Sweet Potatoes(Ipomoea batatas)
Purple-Fleshed Sweet Potatoes (PFSP) (Ipomoea batatas) are rich sources of acylated anthocyanins. Anthocyanin content, antioxidant activity and total phenols as well as color characteristics of PFSP were determined by UV/visible or fluorescence spectrophotometry and chromametry. The flesh of PFSP cultivar Terlaje produced in the Western Pacific contained total anthocyanins at 0.40 mg g-1 fresh weight. PFSP Powders processed by directly freeze-drying or first steaming and then freeze- or hot air-drying contained anthocyanins at 0.94-0.97 mg g-1, Oxygen Radical Absorbance Capacity (ORAC) at 70.0-93.0 μmole Trolox g-1, Trolox Equivalent Antioxidant Capacity (TEAC) at 11.8-12.7 μmole Trolox g-1 and total phenols at 4-5 mg gallic acid g-1 dry weight. PFSP powder processed by hot air-drying without steaming lost 65% of anthocyanin content, 35% of antioxidant activityand 40% of total phenols. Steaming of PFSP roots at atmosphere pressure for 0.5 h increased 40% of anthocyanin content and enhanced the purple color of PFSP. Dehydration at 60°C for 24 h retained anthocyanin content and purple color of steamed PFSP. Both steaming and dehydration increased the percentage of polymeric anthocyanins in PFSP. The results suggested the PFSP powders exhibited potentials as colorants and neutraceutical ingredients for formulated foods.