Transcript ANTIOXIDANT - Dr rer. nat. Rubin Gulaboski

ANTIOXIDANT
Antioxidants
The chemical compounds which can delay the start or slow
the rate of lipid oxidation reaction in food systems.
Mechanism of Antioxidant
14
CH3
Initiation
13
12
11
10
9
(CH2)3 CH2 CH CH CH2 CH CH
CH2 R
Metal
Energy
Reactive oxygen species
Substrate effect
-H
Lipoxygenase
13
C H3
12
11
(C H 2) 4 C H C H C H
E0= 600mv

10
9
CH CH
+ 3O2
K=109/sec
C H2
R
Oxygen consumption,
Conjugated diene
Electron spin resonance
13
CH3
12
11
10
(CH2)4 CH CH CH
O
Propagation
O
E0=1000mv

9
CH CH
CH2 R
(K= 10o M-1sec-1)
+  H from RH (triglyceride)
R.
(K= 107 M-1sec-1)
OH
C(CH 3 )
+  H from
3
C(CH 3 )
3
OCH3
E = 300-500mv
0
.
O
OCH3
13
CH3
12
11
10
9
(CH2)4 CH CH CH CH CH
CH2
R
O
Peroxide value
O
Transition Metal
H
13
C H3
(C H )
2 4
-
Most reactive oxygen species
 OH
E0=2300 mv
12
11
CH CH CH
10
9
CH CH
C H2
R
O

E0=1600 mv
Termination
C H3
C H3
(C H 2) 4
C HO
Sensory evaluation
(C H )
C H3
Volatile compounds
2 3
Are you ready to fight the attack of prooxidants?
O-2, 1O2, .OH, H2O2,
Antioxidant
Prooxidant Jail
R•, RO•,
ROO•,
1O ,
2
O-2,
-OH, H2O2,
Cu, Fe
Cu, Fe.
R•, RO•, ROO •
Preventive Antioxidants





Superoxide dismutase
Catalase
Glutathione peroxidase
Singlet oxygen quencher
Transition metal chelators (EDTA)
Preventive antioxidants minimize the formation of
initiating radicals
Superoxide dismutase
2O2·- Superoxide dismutase
2H+
H2O2 Catalase
O2 + H2O
Glutathione Oxidase
2GSH
GSSG + 2H2O
Glutathione Reductase
NADP+
NADPH + H+
NADP+ Reductase
Gluthione
H
O
C
N
H
C
CH2
CH2
CH2
SH
HC
NH2
COOH
O
C
H
N
CH2COOH
Singlet Oxygen Quenching Mechanism of
Carotenes
1O
2
3
+ 1-CAROTENE
-CAROTENE
RADIATIONLESS
3O
2
1
+ 3-CAROTENE
-CAROTENE
Prooxidant Activities of Transition Metals
Formations of alkyl free radical by direct reaction with fats and oils.
Fe3+ +
RH
Fe2+ + R
+ H+
Hydroperoxide decomposition to form peroxy or alkoxy radical.
Fe3+
Fe2+
+
+
ROOH
ROOH
Fe2+
Fe3+
+ ROO  + H+
+ RO  + OH -
Activation of molecular oxygen for singlet oxygen formation.
Fe2+
+
O2
Fe3+
+ O 2-
1
O2
Radical Scavenging Antioxidant
•
•
•
•
Vitamin C
Tocopherol
Quercetin
Anthocyanin
Radical scavenging antioxidants break free radical
chain reaction by donating hydrogen to free radicals
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
Resonance Stabilization of Antioxidant Radicals
OH
C(CH3)3
E0 = 300-500mv
OCH 3
O
.
+
E0=1000mv (K= 107 M-1sec-1)
R • , RO • , ROO •
O
C(CH )
33
.
C(CH )
33
OCH
3
OCH
3
O
O
.
C(CH3)
C(CH3)3
.
OCH3
OCH3
RH , ROH , ROOH
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.
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
Antioxidants
OH
OH
C(CH3)3
OCH3
Butylated Hydroxy Anisole
(CH3)3C
C(CH3)3
CH3
Butylated Hydroxy Toluene
Antioxidants
OH
OH
OH
C(CH3)3
OH
OH
COOC3H7
PropylGallate
TBHQ
CHO OH
OH
CHO
OH
OH
OH
OH
CH3CH3
CH
CH3
CH
CH3
CH3
Gossypol
CH3
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).
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 2
Oxidized Antioxidant
Stable Resonance Formation of BHA
OH
C (C H 3 ) 3
O C H3
R , RO  , or ROO 
O
.
O
C (C H 3 ) 3
RH, ROH
or ROOH
+
.
C (C H 3 ) 3
O C H3
O C H3
O
O
.
C (C H 3 ) 3
C (C H 3 ) 3
.
O C H3
O CH3
Tocopherol and Oxygen Reaction
CH3
- tocopherol
H2
OH
H2
CH3
CH3
O
( C H 2) 3C H ( C H 2) 3C H ( C H 2 ) 3C H ( C H 3) 2
CH3
CH3
CH3
O
CH3
CH2
CH3
C H 2C ( C H 2) 3C H ( C H 2) 3C H ( C H 3) 2
OH
CH3
O
CH3
CH3
- tocoquinone
O2
Mechanisms of Metals in Accelerating Lipid Oxidation
Formations of alkyl free radical by direct reaction with fats and oils.
Fe3+ +
RH
Fe2+ + R
+ H+
Hydroperoxide decomposition to form peroxy or alkoxy radical.
Fe3+
Fe2+
+
+
ROOH
ROOH
Fe2+
Fe3+
+ ROO  + H+
+ RO  + OH -
Activation of molecular oxygen for singlet oxygen formation.
Fe2+
+
O2
Fe3+
+ O 2-
1
O2
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)
Metal Ions – EDTA Complex Formation
O
C
O
O
O O
CH2
C CH2
N
CH2
M
N CH2
C
O
CH2
CH2
O
C
O
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.
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 .
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.
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.
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.
Isolation and Identification of Oxidation Product of
2,6-Di-(Tert-Butyl)-4-Methylphenol
HO
C H2
C H2
OH
3,3' ,5,5'-Tetra-Bis-( Tert-Butyl)-4,4'-Dihydoxyl-1,2-Diphenylethane
O
CH
CH
3,3',5,5'-Tetra-Bis-( Tert-Butyl)- Stillbenequinone
O
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
Biochemical Control of Lipid Oxidation
Biochemical Control of Lipid Oxidation in Mayonnaise
Composition of Mayonnaise
Soybean oil
Whole egg
Water
Vinegar
Egg yolk
Glucose
Fructose
Salt
Natural Flavor
Composition (%)
77.0
7.0
7.0
3.0
2.0
1.0
1.0
0.9
0.1
100%
Glucose oxidase/catalase Reaction Mechanism.
Glucose oxidase/catalase reaction:
Glucose Oxidase
2 Glucose + 2O 2 + 2H2O
Catalase
2H2O2
2 Gluconic acid + 2H 2O2
2H 2O + O2
The net chemical reaction is:
Glucose Oxidase
2 Glucose + O2
Catalase
2 Gluconic acid
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)
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
Antioxidants for Different Food Systems
A small surface-to-volume ratio – PG and TBHQ
A large surface-to-volume ratio – BHA and BHT
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.