Which tube setup would indicate that the amylase solution was not contaminated with maltose in the negative control group?

• A. Tube 4: Amylase, Deionized Water, pH 7.0 buffer
• B. Tube 1: Amylase, Starch, Buffer
• C. Tube 2: Amylase, Starch, Buffer, pH 7
• D. Tube 3: Amylase, Starch, Buffer, pH 2

Answer: (C)

The main idea here is to check for a pre-existing reducing sugar (maltose) in the amylase prep by using a setup that would reveal contamination without relying on any starch digestion artifacts. If maltose were already present in the enzyme solution, a reducing-sugar test would show you a positive result even without the substrate being digested.

The setup that best serves this check is the tube that includes starch and is kept at neutral pH. Neutral pH supports typical amylase activity, so you expect maltose to appear only because starch is being digested by the enzyme. If the enzyme were contaminated with maltose, you’d see evidence of reducing sugar beyond what would come from digestion alone, making this tube the clearest indicator of whether contamination is present or not. In other words, under standard conditions this configuration allows you to distinguish genuine enzymatic production of maltose from any pre-existing maltose contaminant, so it best shows whether maltose contamination is absent.