Simple and Rapid Spectrophotometric Method for Selecting Purple-Fleshed Sweet Potato Cultivars with a High Radical-Scavenging Activity

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Purple-fleshed sweet potato (Ipomoea batatas) plants containing anthocyanin pigments display a potent antioxidative activity. An 80 % ethanol extract from purple-fleshed sweet potato cultivars harvested in 2000 showed a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity of 8.6 to 49.0 μmol expressed as Trolox equivalent/g of fresh weight. Although this DPPH radical-scavenging assay is convenient for the direct measurement of the radical-scavenging activity, a simpler and faster method should be developed for estimating the activity of a large number of breeding lines. For this purpose, the characterization of the UV-vis spectrum was performed in an 80 % ethanol extract from the purple-fleshed sweet potato. The extract exhibited absorption maxima near 325 nm and 530 nm due to the presence of cinnamic acids (or their related compounds) and anthocyanins, respectively. The absorbance at 325 nm was more highly correlated with the DPPH radical-scavenging activity than that at 530 nm and showed a correlation coefficient of 0.925. Multiple linear regression analysis using the absorbance of the extract at 325 nm and 530 nm elevated the value of the correlation coefficient to 0.979. When a prediction using this calibration curve was applied to extracts of purple-fleshed sweet potatoes harvested in 2001, a high correlation coefficient of 0.977 was obtained with lower SEP values of 1.686. Measurement of the absorbance of extracts from purple-fleshed sweet potatoes at 325 nm and 530 nm enable to obtain estimates of their DPPH radical-scavenging activity simply and rapidly. This assay could be suitable for selecting breeding lines of purple-fleshed sweet potato with a high DPPH radical-scavenging activity.