Investigation of the fabrication and subsequent emulsifying capacity of potato protein isolate/κ-carrageenan electrostatic complexes

The fabrication of protein-polysaccharide complexes via electrostatic interactions was investigated with a naturally cationic protein, potato protein isolate (PoPI), and an anionic polysaccharide, κ-carrageenan (κC), at unadjusted pH conditions. Moreover, the emulsifying capacity of these electrostatic complexes (PoPI-κC) was assessed. PoPI-κC complexes were prepared with a fixed concentration of PoPI (1 wt %), and varying concentrations of κC (0.01–0.5 wt %), using gentle agitation, followed by sonication to fabricate the complexes. The physicochemical properties of PoPI-κC complexes was assessed in terms of size and surface charge, measured using light scattering techniques and electrokinetic potential, respectively. The emulsifying performance of emulsions prepared with PoPI-κC complexes was assessed as a function of κC, and to PoPI, with respect to initial emulsion droplet size, emulsion stability, interfacial tension and optical microscopy. Addition of κC to a 1 wt % PoPI solution yielded the formation of submicron (∼120 nm) electrostatic complexes up to a κC concentration of ≤0.0375 wt %. Higher concentrations of κC yielded micron sized complexes (>10 μm). Emulsions prepared with PoPI-κC complexes yielded comparable emulsion droplet sizes to that of PoPI alone, with the exception of complexes prepared with κC in the range of 0.05–0.07 wt %. Larger emulsion droplets were observed, as these complexes possessed an electrokinetic potential close to the isoelectric point, resulting in aggregation. Emulsions prepared with PoPI-κC complexes possessed marginally enhanced long-term stability in comparison to emulsions prepared with PoPI alone.