Colorimetric assay measuring inhibition of porcine trypsin hydrolysis of BAPNA substrate by absorbance at 410 nm. BAPNA is a manufactured protein substrate comprising of a color covalently bound to an amino acid. BAPNA has an amino acid with a dye molecule attached to it; enzymatic activity by trypsin breaks the bond between the amino acid and the dye molecule, coloring the clear solution yellow.