High Internal Phase Emulsions of Algae Oil Based on Rapeseed Protein via Salt Extraction Combined With Ultrafiltration

Rapeseed protein, as a valuable plant protein, holds great potential as a natural emulsifier for construction of food-grade high internal phase emulsions (HIPEs). In this work, rapeseed protein, obtained through salt extraction combined with ultrafiltration, was employed as a sole stabilizer to formulate algae oil-based HIPEs. The effects of protein concentration and pH changes on the physicochemical properties of HIPEs are systematically evaluated. The results show that a protein concentration of 0.5 wt% is sufficient to form stable and self-supporting HIPEs. As the protein concentration increases, the droplet size of HIPEs gradually decreases, leading to a more robust structure and enhanced stability. Compared to neutral conditions (pH 7.0), the HIPEs under acidic pH 3.5 exhibit more densely packed emulsion droplets with smaller size and more uniform distribution, contributing to superior mechanical properties (higher G′ and yield stress) as well as preferable thixotropic and creep recovery behaviors, which thereby improve their physical stability during storage, thermal processing, and freeze-thaw cycles. Furthermore, the rapeseed protein-stabilized HIPEs inhibit the oxidation of algae oil, especially at pH 3.5. The results of oral lubrication indicate that the reduction in the friction coefficient is mainly associated with an increase in protein concentration, with minor effect from pH variation. These findings suggest that rapeseed protein is an effective emulsifier for preparing stable and processable HIPEs, especially under acidic conditions, which have great potential for applications in semi-solid emulsion foods or edible oil structuring.