NUTRITIONAL VALUE AND PHYSIOLOGICAL FUNCTIONS OF SWEETPOTATO LEAVES

Recently a new sweetpotato cultivar, ‘Suioh’, was developed by the National Agricultural Research Center for Kyushu Okinawa Region, Japan for utilization as a leafy vegetable. Characteristics of ‘Suioh’ cultivar include good taste and much higher contents of calcium and vitamin K than spinach. Sweetpotato leaves contain a high content of polyphenolics in comparison with 12 kinds of the major commercial vegetables. The polyphenolics were composed of caffeic acid (CA) and five kinds of caffeoylquinic acid derivatives, 3-mono-O-caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di-O-caffeoylquinic acid (3,4-diCQA), 3,5-di-O-caffeoylquinic acid (3,5-diCQA), 4,5-di-O-caffeoylquinic acid (4,5-diCQA), and 3,4,5-tri-O-caffeoylquinic acid (3,4,5-triCQA). These polyphenolics showed various kinds of physiological functions, radical scavenging activity, anti-mutagenic activity, anti-cancer, anti-diabetes, and anti-bacterial activity in vitro or in vivo which may be helpful for maintaining and promoting human health. The physiological function of caffeoylquinic acid (CQA) derivatives with plural caffeoyl group is more effective than with a monocaffeoyl one. Furthermore, commercial products with these physiological functions have been developed from sweetpotato leaves in Japan.