Fig. 1. Papain shows intrinsic peroxidase-like activity. The absorption spectra and colors of TMB in different reaction systems: (a) papain + TMB, (b) H₂O₂ + TMB, (c) papain + TMB + H₂O₂ (other conditions: 100 μL of 100 μg mL⁻¹ papain; 1 mL of 5.0 mM TMB; 1 mL of 50 μM H₂O₂; pH = 3.5; reaction temperature is 35 °C; reaction time is 20 min.).