Distinguishing Peptides Using the Ninhydrin and Biuret Reactions in a Student Experiment

The ninhydrin and biuret reactions are used to detect amino acids and peptides. These reactions are experimentally effective, because vivid color changes are observed in short times. Accordingly, we aimed to develop an experimental teaching material that uses the biuret and ninhydrin reactions to distinguish aqueous solutions of Gly, Gly-Gly, Gly-Gly-Gly, and egg white. The optimal reaction conditions for Gly-Gly in both the ninhydrin and biuret reactions, which are essential for conducting this experiment, were investigated. Distinct color changes were observed for the four solution types, which facilitated their differentiation. Almost 80% of the first-year university students successfully distinguished the four sample types in practical lessons. Student reflections and observations generally provided favorable feedback, which indicated that this experimental teaching material effectively deepened students' understanding of the chemical properties of amino acids and peptides.