Oil-in-Water Emulsions Stabilized by Tyrosinase-Crosslinked Potato Protein and Zein Complexes

The effects of microbial tyrosinase on the properties of potato and corn proteins stabilized o/w emulsions was investigated. Corn zeins (the major corn proteins) and potato proteins are complementary in their amino acid profile and therefore their combination is an excellent non-animal protein source. Concentrated emulsions comprising 40% (w/w) olive oil, 6.1% (w/w) potato protein rich fraction (PP) and 2% (w/w) zein were fabricated and were incubated with tyrosinase for 4 hours at 37°C. Emulsions were characterized by their droplet size distribution, rheological behaviour, creaming resistance and microstructure. Results indicate that the tyrosinase-crosslinked PP-zein stabilized emulsion was more stable in comparison with PP-zein non-crosslinked stabilized emulsion. The increase in stability is attributed to the formation of covalent bonds between potato low molecular weight proteins and α-zeins, as determined by SDS-PAGE analysis. Crosslinked PP-zein stabilized emulsion contained larger particles than the non-crosslinked emulsion and microscopy imaging demonstrated a well-packed construction of overlapping particles. Unlike the Newtonian behaviour of the non-crosslinked emulsion, the crosslinked emulsion exhibited a shear-thinning behaviour with a 150-fold increased viscosity (at a shear rate of 150 s^-1). Accelerated physical stability measurements performed on an analytical centrifuge showed that by crosslinking sedimentation was eliminated suggesting the formation of a self-standing gel-like structure. The study implies that tyrosinase is a valuable tool for the crosslinking of PP-zein complexes which can be used for the formation of a stable, high nutritional concentrated oil-in-water emulsion.