Physicochemical properties and digestibility of thermally induced ovalbumin-oil emulsion gels: Effect of interfacial film type and oil size

To investigate the effect of oil droplets surface film type and droplets size on the physicochemical properties and digestibility of thermally induced ovalbumin-oil emulsion gels, Tween 80 and ovalbumin were selected as individual emulsifiers for the emulsification of sunflower oil at different homogenization speeds (6000, 8000, and 10000 rpm), and the formed emulsions were mixed with ovalbumin matrix solution and then heated to form heat-induced ovalbumin emulsion gels (OEG). The OEG with ovalbumin as emulsifier had higher hardness, water holding capacity (WHC), and surface hydrophobicity, and lower digestibility, spin-spin relaxation time (T2) and free sulfhydryl content than those of the OEG with Tween 80 as the emulsifier (p < 0.05). As the oil droplets size decreased, the hardness increased, WHC increased, the amide A band shifted to lower wavenumbers, digestibility decreased, T2 decreased, free sulfhydryl content decreased, and surface hydrophobicity increased for both OEG (p < 0.05). These results collectively indicated that the physicochemical properties of the OEG are influenced by the property of the oil interfacial film and the size of the oil droplets. The oil droplets surrounded by the interfacial protein film improved the performance of the OEG greatly, and the proteins within its OEG formed a dense gel network structure through hydrophobic aggregation, disulfide bond crosslinking, and hydrogen bonding. The oil droplets with smaller sizes favored the enhancement in the physicochemical properties of the OEG. Changes in the size of oil droplets and the type of film wrapped around them regulated the digestibility of the OEG.