F8 antioxidants
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F8 antioxidants






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    F8 antioxidants F8 antioxidants Presentation Transcript

    •  
    •  Explainthe differences between the three main types of antioxidants.
    •  Anantioxidant is a substance that delays the onset or slows the rate of oxidation Antioxidants are added to foods such as oils, fats and butter to prevent oxidative rancidity.
    •  
    •  either preventing the loss of electrons from fats and oils by donating electrons of their own, thus removing reactivefree radicals which are needed for the propagation step. or reducing the availability of transition metal ions in solution.
    • Types of antioxidantsReducing Free radical Chelating agents scavengers agents
    •  Are electron donors and they remove or reduce the concentrations of oxygen. Reducing agents are oxidized in preference to fats or oils. Rancidity of fats and oils is an oxidation reaction, which occurs by a free- radical mechanism, and is catalysed by transition metal ions. Examples include ascorbic acid(vitamin C) and carotenoids.
    •  Vitamin C is readily oxidized on exposure to air, to form dehydroascorbic acid.
    •  Form stable and less reactive free radicals: ROO• +AH → ROOH + A• Examplesinclude BHA, BHT, TBHQ and tocopherols.
    •  
    •  BHA, BHT, TBHQ and tocopherols (which we will represent as AH) acts as antioxidants as they form relatively stable and unreactive free radicals when they lose a hydrogen atom to the reactive free radicals through homolytic fission. R+ AH → RH + A RO + AH → ROH + A ROO + AH → ROOH + A
    •  Thefree radicals produced, can also remove free radicals in termination steps: R+ A → RA RO + A → ROA
    •  Reduce the concentration of free metal ions in solution. Examples include salts of EDTA and plant extracts (rosemary, tea, ground mustard) EDTA forms especially strong complexes with Mn(II), Cu(II), Fe(III), Pb (II) and Co(III).
    •  A chelate is a chemical compound composed of a metal ion and a chelating agent. A chelating agent is a substance whose molecules can form several bonds to a single metal ion. In other words, a chelating agent is a polydentate ligand. EDTA is a versatile chelating agent. It can form four or six bonds with a metal ion, and it forms chelates with both transition-metal ions and main-group ions.
    • The polydentate ligandEDTA can take the place ofsixmonodentate ligands as ithas six lonepairs available. Metal-EDTA
    •  The removal of the free metal ion from solution as a chelate, means that it is not free to catalyse oxidation reactions. EDTA forms chelates with many metal ions and is widely used as a food additive.