Trials over two years were conducted using 1389 sweetpotato (Ipomoea batatas L.) genotypes collected from all over the world to characterize the polyphenolic composition in sweetpotato leaves. Wide variation was observed in relation to their total and individual leaf polyphenolic constituents. In all genotypes studied, the total polyphenol contents of sweetpotato leaf ranged from 1.42 to 17.1 g/100 g dry weight. The six different polyphenolic compounds were identified and quantified by NMR, FABMS, and RPHPLC analysis procedures. This is the first report of polyphenolic compositions in sweetpotato leaves. The relative levels of polyphenolic acids in sweetpotato leaves were as follows: 3,5-di-O-caffeoylquinic acid > 4,5-di-O-caffeoylquinic acid > chlorogenic acid (3-O-caffeoylquinic acid) > 3,4-di-O-caffeoylquinic acid > 3,4,5-tri-O-caffeoylquinic acid > caffeic acid. The highest 3,4,5-tri-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid occurred at 221 and 1183.30 mg/100 g dry weight, respectively.

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In addition to the nutritionally important components such as starches, vitamins and minerals, storage roots and leaves of sweetpotato (Ipomoea batatas) contains several components with health-promoting functions. Of these, the functionalities of carotenoids, anthocyanins and caffeoylquinic acids have been well established by in vitro and in vivo experiments. Several sweetpotato cultivars containing high levels of these components have been developed in Japan; e.g., ‘Ayamurasaki’, which has high amounts of anthocyanin in its storage roots. To further improve the content and also to change the composition of these functional components, the identification of the genes involved in their biosynthesis and genetic modification of the biosynthetic pathway has been attempted. In this review, we summarize the present status of the research and breeding for these functional components, and we discuss the future prospects for improving sweetpotato functionality.