46C-19 |
The double functions of whey protein: Surfactant and antioxidant |
M. HU1, D. J. McClements, and E. A. Decker. (1) Department of Food Science, University of Massachusetts, Chenoweth Lab, Amherst, MA 01003 Whey proteins are not only emulsifying, gelling and bulking ingredients in foods, but can also inhibit lipid oxidation. Therefore, whey proteins represent a food additive that can form physically stable emulsions while altering the properties of the emulsion droplet interface in a manner that increases oxidative stability. The objective was to utilize salmon oil-in-water emulsions stabilized by whey protein isolate (WPI), sweet whey (SW), beta-lactoglobulin (beta-Lg) and alpha-lactalbumin (alpha-La) to get a better understanding of how the interfacial region of emulsion droplets influences factors involved in lipid oxidation. The influence of pH and temperature on the oxidative stability of whey protein-stabilized emulsions was also evaluated. A coarse emulsion containing protein (WPI, or SW , beta-Lg, alpha-La), acetate-imidazole buffer and salmon oil was made by mixing with a Polytron followed by homogenization. Particle size and zeta potential were measured, and lipid hydroperoxide and headspace propanal were used to follow lipid oxidation. Increasing storage temperature (4-37 C) increased lipid oxidation in all emulsions. The pI of WPI in WPI-stabilized emulsions was 4.8 as determined by zeta potential. Formation of lipid hydroperoxides and headspace propanal was much lower at pHs below the pI (positive droplet charge) than pHs above the pI (negative droplet charge). This effect was likely due to the ability of positively charged emulsion droplets to repel iron. In a comparison of lipid oxidation rates between WPI, SW, beta-Lg and alpha-La at pH 3, the oxidative stability was in the order of beta-Lg > SW >WPI >alpha-La . The results indicated that it was possible to engineer emulsions with greater oxidative stability by using proteins to produce positively charged emulsion droplets, thereby reducing or eliminating the need for exogenous food antioxidants.
Session 46C, Food Chemistry: Lipids, antioxidants and emulsifiers
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