The effectiveness of protein measurement using the Folin phenol reagent is largely dependent on its interaction with __________, which can lead to inaccurate results if not properly managed.

The Folin‑phenol reagent reacts strongly with aromatic amino acids such as tyrosine, tryptophan, and phenylalanine, which gives the colour change used to estimate protein concentration. Because the reagent is sensitive to any reducing substance, the presence of other aromatic or reducing compounds can give a false high reading. For example, a sample containing a lot of phenylalanine will produce a colour intensity that looks like a higher protein level, even if the protein amount is low. Thus, accurate results depend on controlling or accounting for these aromatic residues or other reducing agents in the sample.