Establishment of a stable complex formed from whey protein isolate and chitosan and its stability under environmental stresses.

This study aimed to investigate the stability of a complex formed with whey protein isolate (WPI) and chitosan under environmental stress. The optical density, particle size, zeta potential, chemical characteristics, electrostatic interactions, and surface morphology were evaluated for the stable complexes; the optimum conditions for the generation of the stable complex were 0.2% (wt/wt) whey protein with 0.05% (wt/wt) chitosan at pH 5.7. Under these conditions, the complex particle size was 217.8 ± 11.3 nm and the zeta potential was 16.7 ± 0.92 mV. The complex was formed through electrostatic interactions between the amine groups of chitosan (-NH) and carboxyl groups of whey protein (-COO), and contained a porous network interspaced by heterogeneously sized vacuoles. The complex displayed stable physiochemical characteristics under environmental stresses including NaCl (0-75 mM) or sugar (0-5%) at ambient temperature and upon heating for 15 min at 25-65 °C, up to 65 °C for 30 min. Moreover, the complex could be stably stored for 30 d at 4 °C and for 20 d at 25 °C. The present results provide theoretical insights into the industrial production of chitosan-protein complexes and for microencapsulation of sensitive food or medicinal ingredients to increase their intestinal absorption.