1. ANTIOXIDANT

2. Antioxidants
The chemical compounds which can delay the start or slow the rate of lipid oxidation reaction in food systems.

3. Mechanism of Antioxidant C H ( C H ) C H C H C H C H C H C H C H R 3 2 3 2 2 2
Initiation
Metal
Energy
Reactive oxygen species
Lipoxygenase
Substrate effect
-  H C H ( C H ) C H C H C H C H C H C H R 3 2 4  2
E0= 600mv
Oxygen consumption,
Conjugated diene
Electron spin resonance
+ 3O2
K=109/sec

4. . C H ( C H ) C H C H C H C H C H C H R Propagation O C H ( C H ) C H C H C H C H C H C H R 3 2 4 2
Propagation O
(K= 10o M-1sec-1)
+  H from RH (triglyceride) O R. 
E0=1000mv
(K= 107 M-1sec-1) . O H O C ( C H )
+  H from 3 3 C ( C H ) 3 3 O C H 3 O C H 3
E0 = mv

5. Most reactive oxygen species C H ( C H ) C H C H C H C H C H C H R 3 2 4 2 O
Peroxide value O
-  OH
Most reactive oxygen species
Transition Metal H
E0=2300 mv C H ( C H ) C H C H C H C H C H C H R 3 2 4 2 O 
E0=1600 mv
Termination
Sensory evaluation
Volatile compounds C H ( C H ) C HO 3 2 4 C H ( C H ) C H 3 3 2 3

6. Are you ready to fight the attack of prooxidants?
O-2, 1O2, .OH, H2O2,
Cu, Fe. R•, RO•, ROO •
Antioxidant
Prooxidant Jail
R•, RO•, ROO•,
1O2, O-2,
-OH, H2O2,
Cu, Fe

7. Preventive Antioxidants
Superoxide dismutase
Catalase
Glutathione peroxidase
Singlet oxygen quencher
Transition metal chelators (EDTA)
Preventive antioxidants minimize the formation of initiating radicals

8. Superoxide dismutase Catalase Superoxide dismutase 2O2·- H2O2 O2 + H2O
Glutathione Oxidase
GSSG + 2H2O
2GSH
Glutathione Reductase
NADP+
NADPH + H+
NADP+ Reductase

9. Gluthione H H H O O C N C C N
CH2COOH
CH2
CH2
CH2 SH HC
NH2
COOH

10. Singlet Oxygen Quenching Mechanism of Carotenes
1O -CAROTENE O -CAROTENE
3 -CAROTENE -CAROTENE
RADIATIONLESS

11. Prooxidant Activities of Transition Metals
Formations of alkyl free radical by direct reaction with fats and oils. Fe 3+ + RH Fe 2+ + R
+ H +
Hydroperoxide decomposition to form peroxy or alkoxy radical. Fe 3+ +
ROOH Fe 2+
+ ROO
+ H + Fe 2+ +
ROOH Fe 3+
+ RO -
+ OH
Activation of molecular oxygen for singlet oxygen formation. Fe 2+ + O Fe 3+
+ O - 1 O 2 2 2

12. Radical Scavenging Antioxidant
Vitamin C
Tocopherol
Quercetin
Anthocyanin
Radical scavenging antioxidants break free radical chain reaction by donating hydrogen to free radicals

13. Standard One-Electron Reduction Potential
Compounds E (mV)
HO· H+ / H2O
RO· H+ / ROH
HOO. H+ / ROOH
ROO· H+ / ROOH
R· H+ / RH 600
Catechol· H+ / Catechol 530
- Tocopheroxyl· H+ / - Tocopherol 500
Ascorbate· H+ / Ascorbate 282

14. Resonance Stabilization of Antioxidant RadicalsH C ( C H ) 3 3
E0 = mv
E0=1000mv
(K= 107 M-1sec-1) +
R , RO , ROO • • •
RH , ROH , ROOH O C H 3 . O O . C ( C H ) C ( C H ) 3 3 3 3 O C H O C H 3 3 O O . C ( C H ) C ( C H ) 3 3 3 . O C H O C H 3 3

15. Minimization of Lipid Oxidation
If a compound inhibits the formation of free alkyl radicals in the initiation step, or if the chemical compound interrupts the propagation of the free radical chain, the compound can delay the start or slow the chemical reaction rate of lipid oxidation.
The initiation of free radical formation can be delayed by the use of metal chelating agents, singlet oxygen inhibitors, and peroxide stabilizers.
The propagation of free radical chain reaction can be minimized by the donation of hydrogen from the antioxidants and the metal chelating agents.

16. Characteristics of Antioxidants
The major antioxidants currently used in foods are monohydroxy or polyhydroxy phenol compounds with various ring substitutions. These compounds have low activation energy to donate hydrogen. The resulting antioxidant free radical does not initiate another free radical due to the stabilization of delocalization of radical electron.
The resulting antioxidant free radical is not subject to rapid oxidation due to its stability.
The antioxidant free radicals can also react with lipid
free radicals to form stable complex compounds

17. Antioxidants O H C ( ) C ( H ) O Butylated Butylated Hydroxy Anisole3 ) C ( H 3 ) O
Butylated Hydroxy Anisole
Butylated
Hydroxy Toluene

18. Antioxidants Gossypol O H C O H C ( ) Propyl Gallate TBHQ C H O 3 7 3

19. Mechanism of Antioxidants
Hydrogen donation to free radicals by antioxidants.
Formation of a complex between the lipid radical and the antioxidant radical (free radical acceptor).

20. Reaction of antioxidants with radicals+ AH RH + A RO + AH
ROH + A
ROO + AH
ROOH + A R + A RA RO + A
ROA
ROO + A
ROOA
Antioxidant + O
Oxidized Antioxidant 2

21. Stable Resonance Formation of BHA( 3 ) R
, RO
, or ROO . C ( H 3 ) O O C H 3 ( ) .
RH, ROH +
or ROOH C ( H 3 ) O O . C ( C H 3 ) 3 . O C H 3

22. Tocopherol and Oxygen Reaction3 2 ( ) a -
tocopherol C H C H C H 3 3 3 ) C H ( C H ) C H ( C H ) 3 2 3 3 2 O H a -
tocoquinone

23. Mechanisms of Metals in Accelerating Lipid Oxidation
Formations of alkyl free radical by direct reaction with fats and oils. Fe 3+ + RH Fe 2+ + R
+ H +
Hydroperoxide decomposition to form peroxy or alkoxy radical. Fe 3+ +
ROOH Fe 2+
+ ROO
+ H + Fe 2+ +
ROOH Fe 3+
+ RO -
+ OH
Activation of molecular oxygen for singlet oxygen formation. Fe 2+ + O Fe 3+
+ O - 1 O 2 2 2

24. Kinds of Metal Chelators
Metal chelators deactivate trace metals that are free or salts of fatty acids by the formation of complex ion or coordination compounds.
1. Phosphoric acid
2. Citric acid
3. Ascorbic acid
4. Ethylene-Diamine-Tetra-Acetate (EDTA)

25. Metal Ions – EDTA Complex FormationH O 2 C C H 2 O N C H 2 M C H O N 2 C C H C H 2 2 O O C O

26. Synergism in Lipid Oxidation
Synergism occurs when mixtures of antioxidants produce a more pronounced activity than the sum of the activities of the individual antioxidants when used separately.
To have maximum efficiency, primary antioxidants are often used in combination with (1) other phenolic antioxidants, or with (2) various metal chelating agents.

27. Factors Affecting the Efficiency of Antioxidant
1. Activation energy of antioxidants to donate hydrogen should be low
2. Oxidation potential should be high
3. Reduction potential should be low
4. Stability to pH and processing.
5. Solubility in oil should be .

28. Antioxidant Safety
Food Additive, Meat Inspection, and Poultry Inspection Acts.
Total concentration of authorized antioxidants added singly or in combination, must not exceed 200 parts per million by weight
on the basis of fat content of the food.

29. Possible Future Antioxidants
1. Polymeric antioxidant.
2. Antioxidant attached to the packaging materials.
3. Development of new, non-absorbable polymeric
antioxidants for use in foods.

30. Long-Term Safety of Monomeric Antioxidants
Pathological effect.
Carcinogenic potential
Interactions with enzymes
Effects of reproduction
The exact nature of the metabolism rate in man.

31. Isolation and Identification of Oxidation Product of 2,6-Di-(Tert-Butyl)-4-Methylphenol
3,3'
,5,5'-Tetra-Bis-(
Tert-Butyl)-4,4'-Dihydoxyl-1,2-Diphenylethane O C H C H O
3,3'
,5,5'-Tetra-Bis-(
Tert-Butyl)-
Stillbenequinone

32. Ideal Antioxidants No harmful physiological effects
Not contribute an objectionable flavor, odor, or color to the fat
Effective in low concentration
Fat-soluble
Carry-through effect  No destruction during processing
Readily-available
Economical
Not absorbable by the body

33. Biochemical Control of Lipid Oxidation

34. Biochemical Control of Lipid Oxidation in Mayonnaise
Composition of Mayonnaise
Composition (%)
Soybean oil
77.0
Whole egg
7.0
Water
7.0
Vinegar
3.0
Egg yolk
2.0
Glucose
1.0
Fructose
1.0
Salt
0.9
Natural Flavor
0.1
100%

35. Glucose oxidase/catalase Reaction Mechanism.2
Gluconic acid + 2H O 2 2 2 2
Catalase 2H O 2H
O + O 2 2 2 2
The net chemical reaction is:
Glucose Oxidase
2 Glucose + O2
2 Gluconic acid
Catalase

37. Kinds of Antioxidants Natural antioxidants:
1.Tocopherols (delta>gamma>beta>alpha)
2.Nordihydroguaretic Acid (NDGA)
3.Sesamol
4.Gossypol
Synthetic antioxidants:
1.Butylated Hydroxy Anisole (BHA)
2.Butylated Hydroxy Toluene (BHT)
3.Propyl Gallate (PG)
4.Tertiary Butyl Hydroquinone (TBHQ)

38. Choices of Antioxidants
Different antioxidants show substantially different antioxidant effectiveness in different fats and oils and food systems due to different molecular structures.
We should consider the following:
Safety
Antioxidant effectiveness
Off-odor
Off-color
Convenience of antioxidant incorporation to foods
Carry-through effect
Stability to pH and food processing
Availability
Cost
Non-adsorbable, if possible

39. Antioxidants for Different Food Systems
A small surface-to-volume ratio – PG and TBHQ
A large surface-to-volume ratio – BHA and BHT

40. Application of Antioxidants to Foods
Direct addition of antioxidants to oil or melted fat.
Addition of antioxidants to the food after they are diluted in oil.
Spraying antioxidant solution in oil on the food or dipping food into antioxidant solution.