Food Antioxidants
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What are food antioxidants?
Substances that protect foodstuffs from oxidative damage. They act by interacting with highly reactive species such as free radicals, and converting them into stable and less reactive forms.
What are free radicals?
Uncharged molecules or ions with unpaired electrons.
What is auto-oxidation?
spontaneous oxidation of molecules caused by atmospheric O2.
What are the two types of rancidity?
oxidative hydrolytic
What is oxidative rancidity?
off-flavorscausedbyproductsof oxidation, e.g., aldehydes, ketones, alcohols.
What is hydrolytic rancidity?
off-flavorscausedbyliberationof free fatty acids.
Oxidative rancidity is accelerated by
trace metals (Fe, Cu and Zn), salt, light, bacteria, and molds.
Hydrolytic rancidity is accelerated by
water, lipases and phospholipases from bacteria, and molds.
What is total antioxidant capacity (TAC)?
the full or total antioxidant activity against various reactive oxygen/nitrogen species.
What is oxygen radical absorbance capacity (ORAC)?
determines the degradation of an antioxidant (e.g., fluorescein) after being mixed with free radical generators such as peroxyl radicals.
What is total radical antioxidant potential (TRAP)?
the time required to deplete antioxidant(s) by reactive species produced at a given rate.
Give examples of reactive species
• Free radicals (superoxide radical (O2−), hydroxyl radical) • Singlet oxygen (O2*) • Hydrogen peroxide (H2O2) • Peroxynitrite (ONO2−) • Hypochlorous acid (HClO)§
Agents that promote oxidation are:
• Molecular oxygen • High temperature • UV radiation & exposure to light • Metal ions (pro-oxidants) • Unsaturated biomolecules
What are the steps of auto-oxidation
• initiation • propagation • termination
What are the reactions that occur in the initiation step in auto-oxidation?
X• + R−H –> R• + H−X
What are the reactions that occur in the propagation step of auto-oxidation?
R• + O2 –> ROO• ROO• +R−H –> ROO−H+ R•
What are the reactions that occur in the termination step of auto-oxidation?
2 ROO• –> ROO−R + O2 ROO• + R• –> ROO−R R• +R• –> R−R
What can be reactions of “alternative initiation”?
ROO−H –> RO• + •OH 2ROO−H –> RO• + ROO• + H2O
What are the reactions of metal ion induced alternative initiation?
Mn++ROO−H –> RO•+−OH +M(n+1)+ M(n+1)+ + ROO−H –> ROO• + H+ + Mn+
What are the types of antioxidants?
Primary antioxidants (free radical scavengers) Secondary antioxidants (non free radical deactivators)
Give examples of primary antioxidants (free radical scavengers)
• vitamin C • vitamin E • carotenoids • flavonoids
Demonstrate the reaction that phenolic antioxidant (tocopherol) can undergo
in the slides (16)
What are the two types of secondary antioxidants?
Preventive Antioxidants The non free radical deactivators
Give examples for preventive antioxidants
• Metal ion chelators (ferretin, lactoferrin, amino acids, peptides, proteins) • Non-radical decomposition of hydroperoxides & hydrogen peroxide