The seeds of Phaseolus vulgaris contain an inhibitor of alpha-amylase and identified in the protein fraction of the bean. This protein binds with the active sites of alpha-amylase and prevents the starch metabolizing activity; hence it is also called as “Starch Blocker”.

The alpha-amylase inhibitor is a protein composed of two glycosylated protomers of 30 kDa, which are cleaved into two polypeptides of 16 and 14 kDa, respectively (Moreno and Chrispeels, 1989).