Effects of Peach Kernel Protein Isolates on the Physical and Oxidative Stability of Water-in-oil Emulsions
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Abstract:
A water-in-oil (W/O) emulsion was prepared using a microfluidizer, with walnut oil rich in polyunsaturated fatty acids as the oil phase. Peach kernel protein isolates (PKPIs) were added to the aqueous phase, and the emulsion was stored in the dark at 45?C. The particle size distribution, mean particle size, and other physical properties were measured on alternate days, and the primary oxidation products (lipid hydroperoxides) and secondary oxidation product (headspace hexanal) were determined in order to evaluate the influence of aqueous phase PKPI on the stability of W/O emulsions. The results showed that the application of PKPIs could reduce the emulsion droplet size and improve the physical stability of W/O emulsions. Additionally, PKPIs show antioxidant activity; at the concentration range of 0.1~0.4 wt%, the physical and oxidative stability of W/O emulsions increases with the increasing PKPI concentrations. Aqueous phase pH had a significant effect on the oxidative stability of emulsions. The antioxidant activity of PKPI at aqueous phase pH 7.0 was higher than that at pH 3.0. Calcium ionic strength of aqueous phase also had an important impact on the stability of PKPI W/O emulsions. When the concentration of CaCl2 was in the range of 100-200 mM, the physical stability of the emulsions increased with increasing ionic strength. At low levels of calcium ionic strength of aqueous phase in the emulsion (≤10 mM CaCl2), a high ionic strength was able to suppress the antioxidant activity of PKPI. At a high level of calcium ionic strength (≥ 100 mM CaCl2), a high ionic strength was able to accelerate lipid oxidation in the emulsions.
