Effect of water‐binding agents on the catalyzed oxidation of methyl linoleate

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Abstract
Autoxidation of methyl linoleate was studied in model systems containing added metals and different water‐binding agents including cellulose, dextran and glycerol. In all systems, addition of water was increasingly antioxidant up to a critical level of water activity, above which further additions promote oxidation. The specific level of water activity at which oxidation rates are minimal and the water contents at this critical activity depend on the composition of the system. Results of the present study and much of the conflicting data in the literature can be explained as follows. A small amount of water is tightly bound to polysaccharides and does not affect lipid oxidation. Additional amounts of water are antioxidant because of their ability to hydrate metallic catalysts and to form hydrogen bonds with hydroperoxides. At high water contents the water's solvent action mobilizes catalysts, thereby overcoming the antioxidant effects. The present study indicates that water bound to glycerol is still capable of mobilizing catalysts. Depression of water activity by addition of agents such as glycerol has different effects on oxidation than does depression of water activity by other means. Interaction between the effects by system composition and water activity must be considered when either is varied to maximize storage stability of foods