Spectrophotometric assay measuring inhibition of yeast alpha-glucosidase by sample extracts using p-nitrophenyl-α-D-glucopyranoside (pNPG) hydrolysis to p-nitrophenolate, detected at 405 nm. Alpha-glucosidase inhibitors inhibit the absorption of carbohydrates from the small intestine. They competitively inhibit enzymes that convert complex non absorbable carbohydrates into simple absorbable carbohydrates. These enzymes include glucoamylase, sucrase, maltase, and isomaltase.