ANTIOXIDANT

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
14 13 12 11 10 9
C
H
C
H
C
H
C
H
C
H
C
H
C
H
R
(
C
H
)
C
H
2
2
2
2
3
3
Initiation
Metal Energy Reactive oxygen species Lipoxygenase
Substrate effect
- ? H
13 12 11 10 9
(
C
H
)
C
H
C
H
R
C
H
C
H
C
H
C
H
C
H
2
4
3
2
?
Oxygen consumption, Conjugated diene Electron
spin resonance
E0 600mv
3O2
K109/sec
4
13 12 11 10 9
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
R
C
H
2
4
3
2
O
Propagation
(K 10o M-1sec-1) ? H from RH (triglyceride)
R.
O
?
E01000mv
(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 300-500mv
5
13 12 11 10 9
C
H
C
H
C
H
C
H
C
H
C
H
R
(
C
H
)
C
H
2
2
4
3
O
Peroxide value
O
Most reactive oxygen species
- ? OH
Transition Metal
H
E02300 mv
13 12 11 10 9
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
R
C
H
3
2
2
4
O
?
E01600 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
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Preventive Antioxidants

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

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Superoxide dismutase
Catalase
Superoxide dismutase
2O2- H2O2 O2
H2O
2H
Glutathione Oxidase
GSSG 2H2O
2GSH
Glutathione Reductase
NADP
NADPH H
NADP Reductase
9
Gluthione
H
H
H
O
N
C
N
C
C
CH2COOH
O
CH2
CH2
SH
CH2
NH2
HC
COOH
10
Singlet Oxygen Quenching Mechanism of Carotenes
1O2 1?-CAROTENE 3O2
3?-CAROTENE 3 ?-CAROTENE
1 ?-CAROTENE
RADIATIONLESS
11
Prooxidant Activities of Transition Metals
Formations of alkyl free radical by direct
reaction with fats and oils.
3
2

Fe

RH
Fe

R
H

Hydroperoxide decomposition to form peroxy or
alkoxy radical.
3
2

Fe

ROOH
Fe
ROO
H

2
3
-
Fe

ROOH
Fe
RO
OH

Activation of molecular oxygen for singlet oxygen
formation.
2
3
-
1
Fe

O
Fe
O

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 2310 RO H /
ROH 1600 HOO. H / ROOH 1300 ROO H
/ ROOH 1000 R H / RH 600 Catechol
H / Catechol 530 ?- Tocopheroxyl H / ?-
Tocopherol 500 Ascorbate H / Ascorbate 282

14
Resonance Stabilization of Antioxidant Radicals
O
H
C
(
C
H
)
3
3
E01000mv
(K 107 M-1sec-1)
E0 300-500mv

RH , ROH , ROOH
R , RO , ROO



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
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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.
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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
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Antioxidants
Butylated Hydroxy Anisole
Butylated
Hydroxy Toluene
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Antioxidants
Propyl
Gallate
TBHQ
Gossypol
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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).
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Reaction of antioxidants with radicals
R

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
R
, RO
, or ROO



.
RH, ROH or ROOH
O
.
C
(
C
H
)
3
3
.
O
C
H
3
22
Tocopherol and Oxygen Reaction
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.
3
2

Fe

RH
Fe

R
H

Hydroperoxide decomposition to form peroxy or
alkoxy radical.
3
2

Fe

ROOH
Fe
ROO
H

2
3
-
Fe

ROOH
Fe
RO
OH

Activation of molecular oxygen for singlet oxygen
formation.
2
3
-
1
Fe

O
Fe
O

O
2
2
2
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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)
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Metal Ions EDTA Complex Formation
O
C
O
C
H
O
2
C
C
H
2
N
O
C
H
2
M
C
H
2
O
N
C
H
C
C
H
2
2
O
O
C
O
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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.
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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 .
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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.
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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.
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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.
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Isolation and Identification of Oxidation Product
of 2,6-Di-(Tert-Butyl)-4-Methylphenol
H
O
C
H
C
H
O
H
2
2
3,3'
,5,5'-Tetra-Bis-(
Tert-Butyl)-4,4'-Dihydoxyl-1,2-Diphenylethane
C
H
C
H
O
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 Car
ry-through effect ? No destruction during
processing Readily-available Economical Not
absorbable by the body
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Biochemical Control of Lipid Oxidation
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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.
Glucose oxidase/catalase reaction
Glucose Oxidase
2 Glucose 2O
2H
O
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
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37
Kinds of Antioxidants
Natural antioxidants 1.Tocopherols
(deltagtgammagtbetagtalpha) 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-ad
sorbable, 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.