8-2 |
Prooxidative metals: Why where they are can dictate their reactivity |
E. A. DECKER and D. J. McClements. Dept. of Food Science & Nutrition, Univ. of Massachusetts, Amherst, 236 Chenoweth Bldg., Amherst, MA 01003 Both hydroperoxides and transition metals are common in lipid-containing foods. A combination of metals and hydroperoxides can lead to formation of free radicals that promote the oxidative deterioration of foods. The importance of metal-promoted hydroperoxide decomposition on lipid oxidation rates in foods has been known for some time as food processors have commonly used chelators to increase oxidative stability. However, little is known about how the physical properties of foods influences this important oxidative reaction. Emulsion droplets stabilized by anionic emulsifiers attract metals to the emulsion droplet surface where they can promote lipid hydroperoxide breakdown resulting in increased lipid oxidation rates whereas emulsions stabilized by nonionic and cationic surfactants are more oxidatively stable. Similarly, protein-stabilized oil-in-water emulsion droplets will bind prooxidant metals causing rapid oxidation at pH's above their pI's where the emulsion droplet is negatively charged. The thickness of the interfacial membranes of emulsion droplet is also important with surfactants with large polar head groups decreasing transition metal-hydroperoxide interactions thus decreasing oxidation rates of emulsified lipids. Compounds that influence the binding of transition metals to the surface of emulsion droplets will also alter the oxidative stability of oil-in-water emulsions. Sodium chloride, ethylenediamine tetraacetic acid, phytate and whey proteins will all decrease emulsion droplet-metal binding and lipid oxidation rates. Ingredients that contain hydroperoxides such as surfactants can also decrease the stability of lipids and antioxidants with surfactant hydroperoxides increasing fatty acid, a-tocopherol and salmon oil oxidation rates. This research highlights the importance of transition metal-hydroperoxide interactions on the oxidative stability of oil-in-water emulsion. A better understanding of the factors that influence metal-hydroperoxide interactions could lead to the development of new technologies to produce oxidatively stable foods.
Session 8, Oxidation in heterogenous foods and biological tissues: Impact on food quality and health
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