Download - Oxi Rancid
-
7/30/2019 Oxi Rancid
1/22
OXIDATIVE RANCIDITYBryan Giger
Howard Chua
Alison Alcaraz
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
2/22
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
3/22
OXIDATIVE RANCIDITY
Oxygen breaks down double bonds in unsaturated fats through
the free radical process
Three stages:
Initiation
Propagation
Termination
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
4/22
INITIATION
Formation of free radicals
RH -> R + H
Conditions:
Light (sunlight)
Catalyst (Metal)
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
5/22
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
6/22
TERMINATION
Free Radicals combine into non-radical products
R + R -> RR
R + ROO -> ROOR
ROO + ROO -> ROOR + O2
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
7/22Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
8/22
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
9/22
ANTI-OXIDANTS
3 Types:
1. Free Radical Inhibitors (Scavengers)
2. Complexing Agents (Chelating Agents)
3. Reducing Agents
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
10/22
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
11/22
FREE RADICAL INHIBITORS
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
12/22
FREE RADICAL INHIBITORS
Simplified by the formula AH
Examples:
Vitamin E (Tocopherols)
BHA, BHT, TBHQ
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
13/22
Molecular Formula: C11H16O2
Oxygen Reacts more favorably with BHA or BHT so it acts as agetter and thus preserving food
BHA (BUTYLATED
HYDROXYANISOLE)
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
14/22
BHT (BUTYLATED
HYDROXYTOULENE)
Molecular Formula: C15H24O
Behaves as a synthetic version of Vitamin E
Is a Terminating agent
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
15/22Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
16/22Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
17/22
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)
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
18/22
EDTA4-
(ethylenediaminetetraacetic acid)
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
19/22
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
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
20/22
REDUCING AGENTS
Examples:
Vitamin C
Carotenoids
-Carotene
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
21/22
VITAMIN C
(ASCORBIC ACID)
Half Equation of Vitamin C
Wednesday, December 12, 12
-
7/30/2019 Oxi Rancid
22/22
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