Quantifies alpha-amylase by starch hydrolysis to reducing sugars (maltose) detected via DNS colorimetry at 540 nm. The reducing sugars donate electrons to the DNS. The DNS (3,5-dinitrosalicylic acid) is reduced into a new molecule called 3-amino-5-nitrosalicylic acid. As this chemical reduction happens, the liquid changes color from its original pale yellow to a deep orange-red or dark brown.