Changes in Contents of Caffeic Acid and Seven Species of Caffeoylquinic Acids in Sweet Potato Cultivar "Suioh" Leaves During Boiling Treatment

During boiling treatment of sweet potato cultivar, "Suioh" leaves, the contents of caffeic acid (CA), 3-caffeoylquinic acid, 5-caffeoylquinic acid, 3,5-dicaffeoylquinic acid and 3,4,5-tricaffeoylquinic acid (3,4,5-triCQA) were significantly decreased. However, no significant changes of 4-caffeoylquinic acid and 3,4-dicaffeoylquinic acid were observed, and the content of 4,5-dicaffeoylquinic acid was significantly increased. When each standard solution of CA and caffeoylquinic acids (CQAs) were heated to 100 degrees C, structural isomers were generated from mono-CQAs and di-CQAs, although no significant changes were observed in CA and 3,4,5-triCQA. Therefore, differences in the contents of CA and CQAs during boiling treatment of "Suioh" leaves might be attributed to the formation of structural isomers of mono-CQAs or di-CQAs, in addition to the broth outflow of CA and CQAs in the leaves.