Concentrated Pickering emulsions stabilised by hemp globulin–caseinate nanoparticles: tuning the rheological properties by adjusting the hemp globulin : caseinate ratio

Abstract

Industrial hemp (Cannabis sativa L.) is an underutilised novel protein source. However, the utilisation of hemp seed protein is limited by its low solubility in water. Soluble nanoparticles were made by complexing hemp globulin (HG) with sodium caseinate (SC) via a pH-cycling method. Oil-in-water Pickering emulsions were made with these co-assembled protein nanoparticles. The emulsions were composed of 70% oil phase and 30% water phase (v/v), and contained 2% protein (w/v, pure SC or HG–SC nanoparticles with an HG : SC ratio of 1 : 2 or 1 : 1). All emulsions were stable during 21 days of storage, as there was no phase separation, coalescence or flocculation. At day 0, all emulsions were solid-like (G′ > G′′) regardless of the protein composition. The rheological properties of the emulsions during storage could be tuned by controlling the HG : SC ratio in the HG–SC nanoparticles, i.e. the emulsions became more solid-like over time when there was more HG in the nanoparticles. In contrast, emulsions stabilised by pure SC became more liquid-like during storage. The internal structure and interactions within the emulsions were evaluated by fitting frequency sweep test data according to a co-operative theory of flow. The result suggested that the solid-like emulsion resulted from stronger short-range interactions between flocs of oil droplets, which developed during storage when there was more HG in the HG–SC nanoparticles, and not from the formation of a three-dimensional network. These HG–SC nanoparticles can be used to control the rheological properties of an emulsion during its shelf life.