Complex coacervation behavior and the mechanism between rice glutelin and gum arabic at pH 3.0 studied by turbidity, light scattering, fluorescence spectra and molecular docking

Complex coacervation of mixtures of rice glutelin (RG) and gum arabic (GA) at fixed pH 3.0 as affected by mass ratio, NaCl and urea were investigated. The interaction mechanism of RG-GA complex was analyzed using fluorescence spectra and molecular docking. The maximum yield of coacervates occurred at the biopolymer-mixing ratio of 1.0 RG/GA or 1.4 GA/RG. As the NaCl concentration increased from 0 to 100 mmol/L, maximum complex formation occurred at a mass ratio from 1.0 RG/GA to 4.0 RG/GA. The presence of urea possibly induced the formation of RG - GA complex with different structures. The binding constant (Ka) ranged from 2.20 × 105 to 1.67 × 105 L/mol, which indicated that the interaction between RG and GA was exothermic. And the binding process was spontaneous (ΔG < 0). The molecular docking results revealed the major intermolecular forces between RG and GA, and additionally indicated that hydrogen bonding and hydrophobic interaction were also the main force driving the RG-GA complex coacervation, just like electrostatic interaction. This study provides theoretical and methodological information for expanding the use of rice protein as functional components in food products.