Improved stabilization of nanoemulsions by partial replacement of sodium caseinate with pea protein isolate

In this research, pea protein isolate (PPI) was used to partially replace sodium caseinate (SC) in the formation and long-term stabilization of 5 wt% oil-in-water nanoemulsions. Both SC and PPI alone and their 1:1 mixture, at various total protein concentrations, were used to prepare the nanoemulsions using a high-pressure homogenizer. The presence of both the proteins at the oil droplet interface was confirmed by SDS-PAGE analysis of interfacial protein from the mixed-protein-stabilized nanoemulsions. All SC-stabilized nanoemulsions (d32 < 200 nm) displayed creaming due to depletion flocculation by excess proteins. PPI alone also failed to produce stable flowable nanoemulsions (d32 > 200 nm) due to excessive droplet and protein aggregation. Interestingly, nanoemulsions stabilized by 1:1 mixture of SC and PPI did not display any creaming or aggregation and remained stable for more than 6 months (d32 < 200 nm). It was proposed that under high-pressure homogenization disrupted pea proteins aggregate interacted with SC in the continuous phase of the nanoemulsions, which prevented depletion flocculation effect of SC by increasing the size and decreasing the number-density of the depletants and interfered with PPI aggregation thereby blocking both the destabilization mechanisms seen in individual protein-stabilized nanoemulsions. The interaction between the SC and PPI in the aqueous phase were confirmed by the change in surface hydrophobicity and intrinsic fluorescence of the homogenized mixed-protein solutions. The proposed method could be a novel way of utilizing plant proteins in the long-term stabilization of nanoemulsions in the food and beverage industry.