Lipid oxidation
Lipid oxidation another reaction, which severely limits the shelf life of frozen product, which leads to loss of quality (taste, appearance, nutritional value, and protein functionality). Lipid oxidation is a complex process which goes on free radical processes (Erickson, 1997). During the stage of initiation of the hydrogen atom is removed from fatty acids, leaving fatty acid alkyl radical, which is converted in the presence of oxygen to the fatty acid peroxide radical. In the next step, peroxyl radical subtracts hydrogen from neighboring fatty acids to form molecules heme, and new fatty acid alkyl radical. Breakdown of hydroperoxide responsible for the further spread of free radical processes. Decomposition of cumene hydroperoxide, balanced fatty acids, aldehydes and ketones is responsible for the typical aromas (rancidity).
Redox-active transition metals are the main factors catalyzing the oxidation of lipids in biological systems; iron in particular, the famous catalyst. Both enzymatic and non-enzymatic pathways can initiate lipid oxidation.
One of the enzymes are considered important in lipid oxidation-lipoxygenase, which is present in many plants and animals, and can generate offensive tastes, as well as loss of pigment color. Lipid oxidation is especially important in meat (including poultry and seafood. Fatty meats and fish, in particular, suffer from the adverse reactions during long-term frozen storage.
Oxidative taste wear is made in both plant and animal products. It is identified more with frozen muscles than with frozen vegetable products, because blanching, as a rule, used for vegetables before freezing.
Pigment degradation and color quality deterioration is also refer to the oxidation of lipids. Heme pigments in red meat, and carotenoids-fading salmon flesh, undergo oxidative degradation during storage. Chlorophyll-this can also serve as a secondary raw material in the oxidation of lipids.
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Food refrigeration and freezing