Polysaccharide microgel particles-dominated Pickering emulsion gels for oil structuring: Formation, interfacial layer construction, and physical properties

Plant-derived polysaccharides have been gaining much attention for structuring liquid vegetable oils. In this work, the natural κ-carrageenan was mechanically treated to fabricate the nano-sized microgel particle (MP) as Pickering particles for preparing the Pickering emulsion gel (PEG). MPs, acting as building blocks, adsorbed at the surface of emulsion droplets and physically interacted with each other to gel the Pickering emulsion. Macroscopic and microscopic characterizations of MPs and PEGs were carried out. The moderate K+ (0-125 mM) could increase the flocculation and hardness of MPs to improve the viscoelasticity of PEGs. However, due to the K+-inducing shrinkage of κ-carrageenan hydrogels, the excessive K+ (250 mM) would make MPs unable to stabilize PEGs. Prepared MPs were more favorable for forming PEGs when pH was 8 and 9. The oil fraction (10, 20, 30, 40, and 50%) impacted physical properties of PEGs slightly. Three steps for the adsorption of κ-carrageenan MPs to the interface were proposed by tracking the formation of the interfacial layer using the interfacial rheological technique: (1) MPs moved to the interface from the continuous phase, forming the unsaturated adsorption layer; (2) MPs gradually covered the entire interface and began to interact with each other; (3) the adsorption was saturated, and MPs squeezed and interacted to form a compact viscoelastic interfacial layer. This green edible PEG based on sustainable plant-derived κ-carrageenan would provide great potentials in food applications, such as animal-derived solid fats replacement. Compared with the traditional PEG, κ-carrageenan microgel-based Pickering emulsion could gel itself with the low oil phase, which greatly reduced the calorie intake and helped to reduce the total content of saturated fat in high-calorie products (ice cream, chocolate, etc.). These findings can promote applications of structured vegetable oils as vital soft materials in replacing trans and saturated fats in foods.