oxi rancid

7/30/2019 Oxi Rancid

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OXIDATIVE RANCIDITYBryan Giger

Howard Chua

Alison Alcaraz

Wednesday, December 12, 12


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DEFINITION

What is Rancidity?

Causes Undesirable odors and taste in food

Is the decomposition of fats, oils and other lipids

There are three types

Hydrolytic - water splits fatty acids

Microbial - Microorganisms break down food

Oxidative - Oxygen breaks down unsaturated fatty acids



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OXIDATIVE RANCIDITY

Oxygen breaks down double bonds in unsaturated fats through

the free radical process

Three stages:

Initiation

Propagation

Termination



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INITIATION

Formation of free radicals

RH -> R + H

Conditions:

Light (sunlight)

Catalyst (Metal)



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PROPAGATION

Free-Radical chain reactions

R + O2 + -> ROO

ROO + RH -> R + ROOH

As these reactions happen, peroxide radicals are formed andthese in turn react with more unsaturated fatty acids, keeping thereaction continuous



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TERMINATION

Free Radicals combine into non-radical products

R + R -> RR

R + ROO -> ROOR

ROO + ROO -> ROOR + O2



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SYNTHETIC ANTIOXIDANTS

Many synthetic anti-oxidants can be distinguished from theirnatural counterparts by their molecular structure

They are usually phenols with a hydroxyl group attached to abenzene ring

Another group is the tertiary butyl group which has threemethyl groups bound to one carbon



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ANTI-OXIDANTS

3 Types:

1. Free Radical Inhibitors (Scavengers)

2. Complexing Agents (Chelating Agents)

3. Reducing Agents



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FREE RADICAL INHIBITORS

Contain a Phenolic or Tert-Butyl group

Either:

interrupt the formation of free radicals in the initiation step ofauto-oxidation

interrupt the propagation of the chain

They mop-up radicals by forming less stable and less reactiveradicals or form non-radical products



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R + AH -> R-H + A

RO + AH - R-O-H + A

ROO + AH -> R-O-O-H + A

R + A -> R-A

RO + A -> R-O-A



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Simplified by the formula AH

Examples:

Vitamin E (Tocopherols)

BHA, BHT, TBHQ



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Molecular Formula: C11H16O2

Oxygen Reacts more favorably with BHA or BHT so it acts as agetter and thus preserving food

BHA (BUTYLATED

HYDROXYANISOLE)



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BHT (BUTYLATED

HYDROXYTOULENE)

Molecular Formula: C15H24O

Behaves as a synthetic version of Vitamin E

Is a Terminating agent



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COMPLEXING AGENTS

Removes Transition metals (Catalysts)

Acts like a getter for Transition metals

Forms an irreversible complex with metal ions like iron(II) ion Fe2+

This complexing is known as chelating(forming Ligands on

metals)



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EDTA4-

(ethylenediaminetetraacetic acid)



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REDUCING AGENTS

Act just like a reducing agent in a ReDox Reaction

Can react with both oxygen and hydroperoxides produced in theauto-oxidation reaction

Are electron donors that are ably to remove or reduce theconcentrations of oxygen



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REDUCING AGENTS

Examples:

Vitamin C

Carotenoids

-Carotene



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VITAMIN C

(ASCORBIC ACID)

Half Equation of Vitamin C



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RESOURCES/FURTHER

READING

http://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdf
http://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdfhttp://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdfhttp://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdfhttp://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdfhttp://www.foodcanmakeyouill.co.uk/library/content/Antioxidants.pdf

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