Determination of α-amylase inhibitor activity of phaseolamin from kidney bean (Phaseolus vulgaris) in dietary supplements by HPAEC-PAD

Some dietary supplements, so-called ‘starch-blockers’, used to control overweight, are based on the protein concentrate of the kidney bean, known to contain high levels of the α-amylase inhibitor phaseolamin, which may hinder the digestion of complex carbohydrates, thereby promoting or supporting weight loss.Currently, methods to determine the levels of α-amylase inhibitor are based on the measurement of α-amylase activity using colorimetric methods that cannot be applied to dietary supplements because they are complex mixtures of different ingredients that may interfere with the measurement. The aim of this study was to develop an alternative method to determine the level of phaseolamin in dietary supplements, using high-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) to measure the amount of maltose resulting from the action of the enzyme porcine α-amylase on soluble starch in the presence and absence of the inhibitor.The assay described proved sensitive and accurate for use with both dietary supplements and raw materials.