Profiles of phenolics, carotenoids and antioxidative capacities of thermal processed white, yellow, orange and purple sweet potatoes grown in Guilin, China

The objectives of this study were to systematically compare phenolic profiles, carotenoids profiles and antioxidant activities of raw and cooked sweet potatoes of five varieties (white, yellow, orange, light purple and deep purple). Total phenolic content (TPC), monomeric anthocyanin content (MAC), total carotenoid content (TCC), 2-diohenyl-1-picryhydrazyl (DPPH) free radical scavenging capacities and ferric reducing antioxidant powder (FRAP) were determined by colorimetric methods. Higher anthocyanin contents and antioxidant capacities were detected in purple sweet potato species, while higher carotenoid contents were detected in yellow and orange sweet potato. All cooked sweet potato exhibited significantly (p < 0.05) lower TPC, MAC, TCC, DPPH and FRAP values as compared to the respective raw samples. Under the same cooking time, steaming was good for the retention of TPC, roasting was good for keeping anthocyanins, and boiling was beneficial to preserve carotenoids.