Fluorescence spectroscopic analysis of the interaction of papain and bromelain with l-ascorbic acid, α-tocopherol, β-carotene and astaxanthin

•The mechanisms are all static quenching at lower concentrations of antioxidants.•The four antioxidants-papain/bromelain system is driven by enthalpy and entropy.•Electrostatic and hydrophobic interactions are the main forces.•Astaxanthin binds papain in a more firmly way than the other systems.•The four antioxidants may induce microenvironmental changes of papain/bromelain.