Spectrophotometric determination of amylase activity in coloured solutions

A simple procedure for spectrophotometric determination of amylase activity in coloured solutions is described. Starch cross-linked with a bifunctional reagent in the presence of black drawing ink is used as an insoluble chromolytic substrate. The absorbances of reaction mixture filtrates are read in the near-infrared region (at 800-900 nm) where the majority of coloured substances does not absorb; on the contrary, black drawing ink released from the substrate during the action of amylase absorbs strongly even at these wavelengths.