antioxidant. antioxidants the chemical compounds which can delay the start or slow the rate of lipid...
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ANTIOXIDANT
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Antioxidants
The chemical compounds which can delay the start or slow the rate of lipid oxidation reaction in food systems.
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14 13 12 11 10 9
- H
CH2 CH CH CH2 CH CH CH2 R(CH2)3CH3
Initiation
13 12 11 10 9
+ 3O2
(C H2)4
C H3 C H C H C H C H C H
2RC H
Mechanism of Antioxidant
Metal
Energy
Reactive oxygen species
Lipoxygenase
Substrate effect
Oxygen consumption,
Conjugated diene
Electron spin resonance
mv
K=109/sec
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(K= 10o M-1sec-1) + H from RH (triglyceride)
(CH2)4CH3 CH CH CH CH CH2 RCH
O
O
Propagation
13 12 11 10 9
OHC(CH3)
3
OCH3
from
01000mv
0 300-500mv
(K= 107 M-1sec-1)
R.
OC(CH3)
3
OCH3
.
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- OH
CH CH CH CH CH CH2 R(CH2)4CH3
O
O
H
(C H2)4
C H3 C H C H C H C H C H2 RC H
O
C H 3 (C H 2)4 C HO
13 12 11 10 9
13 12 11 10 9
Termination
Most reactive oxygen speciesPeroxide value
(C H2
)3
C H3 C H3
0mv
Sensory evaluation
Volatile compounds
Transition Metal
0mv
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Antioxidant O-2, 1O2, .OH, H2O2,
Cu, Fe. R•, RO•, ROO •
R•, RO•, ROO•,
1O2, O-2,
-OH, H2O2,
Cu, Fe
Prooxidant Jail
Are you ready to fight the attack of prooxidants?
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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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2O2·- H2O2 O2 + H2O
2GSH GSSG + 2H2O
NADP+ NADPH + H+
Superoxide dismutase
2H+
Catalase
Glutathione Oxidase
Glutathione Reductase
NADP+ Reductase
Superoxide dismutase
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Gluthione
HC
COOH
H
CH2
O C N C C N CH2COOH
CH2
CH2
NH2
H O H
SH
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Singlet Oxygen Quenching Mechanism of Carotenes
1O2 + 1-CAROTENE 3O2 + 3-CAROTENE
3 -CAROTENE 1 -CAROTENERADIATIONLESS
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Prooxidant Activities of Transition Metals
Hydroperoxide decomposition to form peroxy or alkoxy radical.
Fe3+ + ROOH Fe2+ + ROO + H+
Fe2+ + ROOH Fe3+ + RO + OH-
Formations of alkyl free radical by direct reaction with fats and oils.
Fe3+ + RH Fe2+ + R + H+
Activation of molecular oxygen for singlet oxygen formation.
Fe2+ + O2 Fe3+ + O-2 1O2
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Radical Scavenging Antioxidant
• Vitamin C • Tocopherol• Quercetin• Anthocyanin
Radical scavenging antioxidants break free radical chain reaction by donating hydrogen to free radicals
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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
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Resonance Stabilization of Antioxidant RadicalsOH
C(CH3)3
OCH 3
C(CH3)3
OCH3
O.
OCH3
C(CH3)3
O
.
C(CH3)3
OCH3
O
.
OCH3
C(CH3)
O
.
R , RO , ROO RH , ROH , ROOH•• •
E0=1000mv 0 300-500mv (K= 107 M-1sec-1)
+
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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
OH
C(CH3)3
OCH3
C(CH3)3(CH3)3C
CH3
OH
Butylated Hydroxy TolueneButylated Hydroxy Anisole
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OH
OHOH
COOC3H7
Propyl Gallate
OH
C(CH3)3
OH
TBHQ
CH
CHO OH
OH
OH
CH3CH3
OH CHO
OH
CH
OH
CH3 CH3CH3 CH3
Gossypol
Antioxidants
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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 radicalsR + AH RH + A
RO + AH ROH + A
ROO + AH ROOH + A
R + A RA
RO + A ROA
ROO + A ROOA
Antioxidant + O2 Oxidized Antioxidant
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Stable Resonance Formation of BHA
O H
C (C H 3)3
O C H 3
R , RO , or ROO
C (C H 3)3
O C H 3
O
O C H 3
C (C H 3)3
O
.
C (C H 3)3
O C H 3
O
O C H 3
C (C H 3 )3
O
RH, ROH +or ROOH
.
..
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O
C H 3 H 2
O H
C H 3
C H 3
H 2
( C H 2 )3 C H ( C H 2 )3 C H ( C H 2 )3 C H ( C H 3 )2
C H 3 C H 3
-tocopherol
O 2
C H 3
C H 3
C H 3
O C H 2
O
C H 2 C ( C H 2 )3 C H ( C H 2 )3 C H ( C H 3 )2
C H 3 C H 3 C H 3
O H
- tocoquinone
Tocopherol and Oxygen Reaction
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Mechanisms of Metals in Accelerating Lipid Oxidation
Hydroperoxide decomposition to form peroxy or alkoxy radical.
Fe3+ + ROOH Fe2+ + ROO + H+
Fe2+ + ROOH Fe3+ + RO + OH-
Formations of alkyl free radical by direct reaction with fats and oils.
Fe3+ + RH Fe2+ + R + H+
Activation of molecular oxygen for singlet oxygen formation.
Fe2+ + O2 Fe3+ + O-2 1O2
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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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O
M
CO
CH2
O CO
CH2
NCH2
CH2
O
O NC
OCH2
COCH2
Metal Ions – EDTA Complex Formation
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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 2 C H 2 O H
3,3' ,5,5'-Tetra-Bis-( Tert-Butyl)-4,4'-Dihydoxyl-1,2-Diphenylethane
C H C H
3,3',5,5'-Tetra-Bis-( Tert-Butyl)- Stillbenequinone
OO
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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
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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 77.0Whole egg 7.0Water 7.0Vinegar 3.0Egg yolk 2.0Glucose 1.0Fructose 1.0Salt 0.9Natural Flavor 0.1
100%
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Glucose oxidase/catalase Reaction Mechanism.
Glucose oxidase/catalase reaction:
2 Glucose + 2O2 + 2H2O 2 Gluconic acid + 2H 2O2
2H2O2 2H2 O + O2
The net chemical reaction is:
2 Glucose + O2 2 Gluconic acid
Glucose Oxidase
Catalase
Glucose Oxidase
Catalase
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Kinds of Antioxidants
Natural antioxidants:1.Tocopherols (delta>gamma>beta>alpha)2.Nordihydroguaretic Acid (NDGA)3.Sesamol4.Gossypol
Synthetic antioxidants:1.Butylated Hydroxy Anisole (BHA)2.Butylated Hydroxy Toluene (BHT)3.Propyl Gallate (PG)4.Tertiary Butyl Hydroquinone (TBHQ)
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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:SafetyAntioxidant effectivenessOff-odorOff-colorConvenience of antioxidant incorporation to foodsCarry-through effectStability to pH and food processingAvailabilityCost
Non-adsorbable, if possible
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Antioxidants for Different Food Systems
A small surface-to-volume ratio – PG and TBHQ
A large surface-to-volume ratio – BHA and BHT
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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.