Effects of Cooking Methods on the Changes of Total Anthocyanins, Phenolics Content and Physical Characteristics of Purple-Fleshed Sweet Potato (Ipomoea batatas L.) Grown in Vietnam

Total anthocyanin content (TAC) and total phenolics in “Nhật tim” purple-fleshed sweet potato (PFSP) variety were analyzed as affected by four cooking methods: steaming, baking, roasting, and frying. Moisture content (%), core flesh temperature (oC) and color characteristics of cooked PFSP were evaluated. TAC in steamed, fried (skin-on), roasted, baked, and fried (skin-off) PFSP were 234.18; 217.14; 208.11; 195.25; 173.68 mg/100g dry weight (DW), respectively. Under the same cooking time, steaming was good for the retention of total phenolics and anthocyanins as compared with baking. Cooking by steaming, roasting, baking, skin-on or skin-off frying produced significant increase (P ≤ 0.05) of TAC and total phenolics as compared to the respective fresh samples. Steaming resulted in the greatest increase of TAC whereas skin-on frying showed a good cooking method to retain high total phenolics (826.47 mg GAE/100g DW) in shred PFSP.