Covalent interactions between walnut protein isolate and chlorogenic acid impact the formation, structure, functionality and emulsions stability of the isolates

Covalents were prepared from chlorogenic acid (CA) and walnut isolated protein (WNPI) by free radical grafting technique and their conformations, functional properties and emulsions stability were investigated. Meanwhile, WNPI-CA covalents were used as a raw material for the preparation of walnut oil emulsions, and the static and dynamic stability of walnut oil emulsions were investigated.The results showed that covalent binding with CA changed the molecular structure and morphology of WNPI, as confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and various spectroscopic techniques methods.The binding of CA with WNPI significantly improved its antioxidant activity, solubility, emulsification properties, foaming, and thermal stability. In addition, the stability of walnut oil emulsions were improved, as evidenced by Zeta potential, rheology, etc. In vitro simulated digestion showed that the WNPI-CA covalents emulsions maintained better antioxidant capacity compared to the WNPI emulsions. In conclusion, this study demonstrates the potential application of WNPI-CA covalents formed by free radical grafting as carriers of functional ingredients in foods and in improving the stability of plant proteins.