Structural transitions of ovalbumin/κ-carrageenan complexes under the effects of pH and composition

Colloid particles consisting of biopolymers such as proteins and polysaccharides have been widely used as food or drug components. Here we investigate the interactions and structures in aqueous mixtures of ovalbumin (OVA) and κ-carrageenan (CRG) to unravel the complexation mechanism. The pH titration results for the OVA/CRG system (0.025%:0.025% by mass) indicate the structural transition of the OVA/CRG complexes happens during acidification. Significant accumulation of insoluble OVA/CRG complex coacervates with OVA packed in the hydrophobic structures formed by CRG occurs when pH is lower than the isoelectric point of OVA. The highest turbidity is reached at pH = 3.0 because of the strongest electrostatic attraction, and further deceasing pH leads to the dissociation of complex coacervates. Composition and ionic strength show significant effects on turbidity and aggregates formation by tuning electrostatic interactions between N–H + of –NH 3 + on OVA and S–O − of –SO 3 − on CRG.