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Role of Metal Ions in Food Oxidation

Role of Metal Ions in Food Oxidation. Food Chemistry April 10, 2014. Neera Munjal. LIPID OXIDATION . Deteriorative Lipid oxidation during storage of fats and oils, muscle based foods. Lead to rancidity, off flavors, color changes, rheological changes, formation of toxic compounds.

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Role of Metal Ions in Food Oxidation

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  1. Role of Metal Ions in Food Oxidation Food Chemistry April 10, 2014 NeeraMunjal

  2. LIPID OXIDATION • Deteriorative Lipid oxidation during storage of fats and oils, muscle based foods. • Lead to rancidity, off flavors, color changes, rheological changes, formation of toxic compounds. • Mechanism of Lipid Peroxidation: Unsaturated fatty acids react with molecular oxygen via free radical chain reaction.

  3. FACTORS ENHANCING LIPID OXIDATION • Metals/Heme Compounds in food enzymes • pH • Water Activity • Form of Metal • Temperature • Processing, Storage • Fat Composition

  4. MECHANISM OF METAL OXIDATION IN FOOD • Oxygen Activation by Metal ions • React with triplet oxygen to form reactive oxygen species • Heme-protein Initiated

  5. HEME INITIATED LIPID OXIDATION • Transition metal ions (Fen+, Cun+, etc) catalyze oxidative changes in tissues. • Muscle pigment (heme) initiated lipid oxidation in muscle based foods. • Myoglobin in beef, pork, broilers • Hemoglobin in broilers, fish • Other sources: Water, Salt • Iron initiates lipid oxidation by generating free radicals.

  6. MYOGLOBIN IN MUSCLE TISSUE PERFERRYL OXY MET DEOXY FERRYL

  7. MET-IRON (III) MYOGLOBIN INDUCED LIPID OXIDATION pH dependent • Acidic pH • Pro-oxidant • Lipid Hydroperoxide formed while conversion of muscle to meat • Physiological pH • Anti-oxidative: Due to formation of non catalytic hemichromepigment (exposure of heme iron to unusual ligands). • Pro-oxidative: High Lipophilic environment result in heme release and exposure of heme to lipids resulting in oxidation (Hematin induced) • Potential pro oxidant at pH found in fresh meat

  8. OXY IRON (II) MYOGLOBIN INDUCED LIPID OXIDATION • Anti-oxidative: Due to formation of non catalytic hemochromes. • Pro-oxidative at high lipid concentration (Hematin induced) • MbFe(II)O2 can promote oxidative modification of LDL • Slaughtering, Low pH in muscle based foods accelerate autoxidation. • Mechanism unclear

  9. IRON (IV) MYOGLOBIN INDUCED LIPID OXIDATION Perferryl • Activation of Met form by H2O2 • It generates unstable hypervalent perferryform. • No oxidation at conditions found in fresh meat. • Can transfer its radicals to other proteins to initiate lipid oxidation. Effect pro oxidant : Ferryl can initiate lipid oxidation at all pH

  10. PREVENTION OF LIPID OXIDATION • Chelating agents such as Citrate anion, EDTA • Nitric Oxide • Control of oxygen by specific processing like deaeration.

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