Hot water extract was prepared from leaves of sweet potato cultivar "Sirnon-1" and the 1,1-diphenyl-2-picrylbydrazyl (DPPH) radical-scavenging activity and polyphenol content of the extract were measured in order to utilize the leaves as a material for tea-like drink with a high radical-scavenging activity. The leaves were harvested at four times (May, June, July and August) in 1998. The highest DPPH radical-scavenging activity was obtained when the leaves harvested at August were extracted at 100degreesC. The HPLC analysis revealed that the dominant radical-scavengers in the hot water extract from the leaves were several polyphenolic compounds beside chlorogenic acid and caffeic acid.
