Genotypic diversity of anthocyanin content and composition in purple-fleshed sweet potato (Ipomoea batatas (L.) Lam)

Sweet potato is one of the ten most important crops for human consumption in the world. Recently, due to the detection of radical scavenging and antioxidative properties, it has been considered that commercial varieties of purple-fleshed sweet potato may play a role in the preservation of health in human beings. In this study, anthocyanin content and composition of 19 purple-fleshed sweet potato clones were investigated to identify the genetic factors responsible for the variation in paste color ranging from reddish purple to bluish purple. The paste color was evaluated based on the color reflectance value L* (related to brightness) and b*/a* ratio tinder for red blue color). Sweet potato clones were classified into two groups based on the b*/a* ratio of the paste:(1) a blue dominant group with a ratio below - 1.4, and (2) a red-dominant group with a ratio above - 1.1. Analysis of the anthocyanins extracted from steamed roots by spectrophotometry and high-performance liquid chromatography (HPLC) revealed considerable differences in the color value and anthocyanin composition among the clones. Based on the peonidin/cyanidin ratio, the sweet potato clones were classified into two groups: cyanidin and peonidin types. The reflectance value L* of the paste was negatively correlated with the color value, while no correlation was found between the b*/a* ratio and the color value. Furthermore, a significant positive correlation was observed between the L* value, b*/a* ratio and peonidin/cyanidin ratio. Especially, the blue dominant clones showing a b*/a* ratio below - 1.4 all belonged to the cyanidin type. These results indicate that in the peonidin types the increase in the peonidin/cyanidin ratio increased the degree of redness of the paste, and in the cyanidin type, the blue color predominated. These findings suggest that it is possible to predict the anthocyanin content and composition roughly by the analysis of the paste color without HPLC investigations. The b*/a* ratio of the paste could be used for the selection of the peonidin type, to obtain a paste with a bright and reddish purple color in sweet potato.