Impact of high-intensity ultrasound on the chemical and physical stability of oil-in-water emulsions stabilized by almond protein isolate

Lipid and protein oxidation always causes the deterioration of foods and their shortened shelf lives. The aim of the present work was to evaluate the effect of high-intensity ultrasound on the chemical and physical stabilities of oil-in-water emulsions comprising a plant-based oil (walnut oil) and protein (almond protein isolate). Emulsions were produced using a three-step procedure: high-shear mixing, sonication, and homogenization. The sonication step was carried out for 30 min at three different energy densities: 0, 200, or 400 J/cm3. Increasing sonic energy densities resulted in much smaller particle size and more droplet charge of the freshly made emulsions. The sonication step also improved the physical stability of emulsified lipids during storage by suppressing the changes in the droplet size and charge. Meanwhile, sonication also inhibited the oxidation of emulsified lipids by decreasing the generation of lipid hydroperoxides and 2-thiobarbituric acid-reactive substances as well as protein by reducing the gain of carbonyls, the loss of free sulfhydryl groups and intrinsic tryptophan fluorescence, and the modification of molecular weights. The highest sonication energy density (400 J/cm3) gave the best results. This study is expected to broaden the application of high-intensity ultrasound in protein emulsion production to improve their quality and acceptability.