Differences in the content of purple pigments, catechinopyranocyanidin A and B, in various adzuki beans, Vigna angularis.

Catechinopyranocyanidin A and B (cpcA, B) are purple pigments isolated from the seed coat of the small red bean called adzuki in Japanese (Vigna angularis). CpcA and B are known to be responsible for the purple color of an-paste. The quality evaluation of the paste is based on its purple color; therefore, it is important to analyze the contents of cpcA and B in various azuki beans, which differ in the cultivar, production area and cultivation conditions. The extraction of cpcA and B from dried beans was conducted, followed by HPLC analysis. The content of cpcA and cpcB in various cultivars from Japan, Korea, China and Nepal were quantified. The cpcA and B content was the highest in the regular adzuki cultivar from Hokkaido Prefecture (Japan), and that of the beans from Korea and China were low. The levels of the pale-colored beans from Nepal were the lowest.