Using a-amylase inhibition as a separation guide, polyphenolic compounds from peanut seed skin were
prepared. During preparation, specific a-amylase inhibitory activities were increased about 4-fold. Highresolution
MALDI-TOF mass spectra showed that the structure of this sample was a series of polyflavan-
3-ols, up to 15-mer, composed of catechin/epicatechin units together with several afzelechin/epiafzelechin
units and gallocatechin/epigallocatechin units. The observed precious mass values suggest that
the polymers consist of both interflavanoid C–C linkages (A-type) and interflavanoid ether linkages
(B-type). Oral administration of the polyphenol fraction to rats fed corn starch significantly suppressed
an increase in blood glucose levels in a dose dependent manner. Administration of the polyphenol fraction
to rats fed maltose or sucrose delayed the increase in blood glucose levels. These results suggest peanut
seed skin contains polyphenols with strong a-amylase inhibitory activity, which retard absorption of
carbohydrates and mainly function through inhibition of a-amylase.