Insights into the interaction between chitosan and pepsin by optical interferometry

Polysaccharides and proteins have attracted increasing interest in the fields of biomedicine and green chemical as biocomposites due to their inherent versatility. Here, we used silica colloidal crystal (SCC) films combined with an ordered porous layer interferometry (OPLI) method to investigate the interaction between chitosan and pepsin at different concentrations and pH values in real time. Zeta potential was combined with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Fourier transform infrared microscopy (FTIR microscopy) to illustrate the interaction mechanism further. The results showed that the variation and slope of the optical thickness (OT) caused by the Fabry-Perot fringes represent the degree and process of interaction. The protonation of chitosan and the net charge carried by pepsin caused various degrees of electrostatic attraction under different pH values. Meanwhile, the rate and degree of hydrolysis were positively correlated with pepsin concentration. This work results provide a theoretical basis for designing novel composites based on the development of polysaccharides and proteins. •Real-time monitoring of the interaction of chitosan-pepsin by optical interferometry•PH and concentration significantly affect the interaction of chitosan-pepsin.•From electrostatic interaction to enzymatic hydrolysis•PH changed the net charge microenvironment carried by chitosan and pepsin.•Concentration was positively correlated with the degree of interaction.