Recently, food-grade Pickering particles, particularly plant proteins, have attracted tremendous attention because they are biobased, environmentally-friendly and edible. To explore the potential of tea water-insoluble protein (TWIP) nanoparticles from tea residues for stabilizing Pickering emulsions, the average hydrodynamic diameter (DH), zeta potential and morphologic profiles of TWIP nanoparticles were characterized using dynamic light scattering (DLS), laser Doppler velocimetry (LDV) and atomic force microscopy (AFM), respectively. The results indicated that TWIP nanoparticles were irregular colloidal particles with a DH greater than 300 nm and a negative charge of more than −30 mV at ionic strengths of 0–400 mM and a fixed TWIP nanoparticle concentration (2.0%). Furthermore, the effect of the TWIP nanoparticle concentration (0.5–4.0%, w/v) and oil-water ratio (2:8–6:4) on the characteristics of the Pickering emulsions stabilized via TWIP nanoparticles was investigated. Increasing the TWIP nanoparticle concentration generated a firm and thick TWIP nanoparticle-based interfacial layer, as verified by Cryo-scanning electron microscopy imaging, and decreased the droplet size of Pickering emulsions at an oil-water ratio of 4:6. Additionally, an increase of the oil-water ratio to 6:4 favored the formation of emulsions with extraordinary creaming stability at the fixed TWIP nanoparticle concentration of 2.0%. The present study is the first to suggest TWIP nanoparticles as a type of food-grade Pickering particle.

The microstructure and stability of oil-in-water emulsions, stabilized with non-protein emulsifiers (sorbitan esters), were analyzed as a function of emulsification time, rotor speed, hydrophilic-lipophilic balance (HLB), and ionic strength. Sauter average dia (D[3,2]) were determined from micrographs. Back-scattered light data were analyzed and a method to determine creaming rates of the systems was proposed. Creaming rates showed that the relationship between emulsion stability and HLB was non-linear. Addition of NaCl raised creaming rates, resulting in decreased stability, while micrographs showed the presence of flocs. Results were discussed taking account of interactions present in the system.

We designed Air-in-Oil-in-Water (A/O/W) emulsions. First, Air-in-Oil foams were fabricated by whipping anhydrous milk fat. The maximum overrun was obtained at 20 °C. The foams contained 30–35 vol% air and were stabilized solely by fat crystals. To refine the bubble size, foams were further sheared in a Couette’s cell. The average bubble size reached a value as small as 6.5 μm at a shear rate of 5250 s−1. The nonaqueous foams were then dispersed in a viscous aqueous phase containing sodium caseinate to obtain A/O/W emulsions. The shear rate was varied from 1000 to 7500 s−1, allowing to obtain Air-in-Oil globules whose average diameter ranged from 15 to 60 μm. To avoid globule creaming, the aqueous phase was gelled by incorporating hydroxyethyl cellulose. Homogeneous emulsions were obtained with fat globules containing around 22 vol% of residual air. The systems were kinetically stable for at least 3 weeks at 4 °C.