Effects of Cooking Methods on Caffeoylquinic Acids and Radical Scavenging Activity of Sweet Potato

The effects of cooking methods, including steaming, deep-frying, and baking, on the phenolic content, 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, and isomerization of caffeoylquinic acids in sweet potato were investigated. A high correlation was observed between antioxidant capacity and total phenolic content. Deep-frying treatment resulted in higher antioxidant capacity with increasing heating time. The major phenolic components of raw sweet potat were 5-caffeoylquinic acid (CQA) and 3,5-dicaffeoylquinic acid (diCQA), which were reduced by heat treatment due to the isomerization of 5-CAQ to 3- and 4-CQA, and 3,5-diCQA to 3,4- and 4,5-diCQA. Moreover, 5-CQA was more stable than 3,5-diCQA even at 100 °C. Our results demonstrated that by controlling the cooking temperature and time, new bioactive compounds such as mono- and diCQA derivatives can be produced from sweet potato. These data indicate a potential approach for the development of new functional foods from sweet potato by controlling cooking temperature and time.