Preparation and characterisation of peanut seed skin polyphenols

• Polyphenols from peanut seed skin were separated using α-amylase inhibition as a guide.
• The polyphenols consist of oligomeric proanthocyanidins with gallic acid.
• The polyphenols strongly inhibited α-amylase activity.
• The polyphenols suppressed an increase in blood glucose levels and area under the curve.

Using α-amylase inhibition as a separation guide, polyphenolic compounds from peanut seed skin were prepared. During preparation, specific α-amylase inhibitory activities were increased about 4-fold. High-resolution 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 α-amylase inhibitory activity, which retard absorption of carbohydrates and mainly function through inhibition of α-amylase.