Effects of Cooking Methods on Anthocyanins and Total Phenolics in Purple-Fleshed Sweet Potato

Abstract

Purple-fleshed sweet potato (PSP) is a rich source of bioactive compounds including anthocyanins and phenolic compounds. Effects of conventional cooking methods (baking, boiling and steaming) on anthocyanins, total phenolic compounds and color were investigated. Six anthocyanin compounds were identified in two cultivars. Total anthocyanins contents in both cultivars were similar with values of 1,591 and 1,539 μg/g dry weights, while the concentrations of individual anthocyanins differ depending on cultivar. Cooking decreased the total anthocyanins content with a range of 844 to 1,249 μg/g dry weight (51–81% of raw PSP) in increasing order of baking > steaming > boiling. Baking and steaming has no influence on the content of the total phenolic compounds, while boiling resulted in a significant decrease (P < 0.05). The redness exhibited a significantly positive correlation with total anthocyanins content. The peonidin/cyanidin ratio was highly correlated with the lightness and yellowness. Practical Applications Recent interest in purple-fleshed sweet potatoes as functional foods has been generated by the high amount of anthocyanins and phenolic compounds. Cooking methods including boiling, baking and steaming decreased the contents of anthocyanins and total phenolics. These results suggest that cooking conditions should be carefully applied to retain the purple color and health beneficial effects of purple-fleshed sweet potatoes.