8/8/2019 10. Antioxidants[1]
1/38
ANTIOXIDANT
8/8/2019 10. Antioxidants[1]
2/38
Antioxidants
The chemical compounds which can delay the start or slow
the rate of lipid oxidation reaction in food systems.
8/8/2019 10. Antioxidants[1]
3/38
14 13 12 11 10 9
- y H
CH2 CH CH CH2 CH CH CH2 R(CH2)3CH3
Initiation
13 12 11 10 9
y
+ 3O2
(C H2
)4
C H3
C H C H C H C H C H2
RC H
Mechanism of Antioxidant
Metal
Energy
Reactive oxygen species
Lipoxygenase
Substrate effect
Oxygen consumption,
Conjugated diene
Electron spin resonance
)!mv
K=109/sec
8/8/2019 10. Antioxidants[1]
4/38
y
(K= 10o M-1sec-1)
+ y H from RH (triglyceride)
(CH2)4CH3 CH CH CH CH CH2 RCH
O
O
Propagation
13 12 11 10 9
OH
C(CH3) 3
OCH3
y ,from
)0!1000mv
)0! 300-500mv
(K= 107 M-1sec-1)
R.
OC(CH3
)3
OCH3
.
8/8/2019 10. Antioxidants[1]
5/38
- y OH
CH CH CH CH CH CH2
R(CH2)
4CH
3
O
O
H
y
(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 )3C H3 C H3
)0!mv
Sensory evaluation
Volatile compounds
Transition Metal
)0!mv
8/8/2019 10. Antioxidants[1]
6/38
Theimagecannot bedisplayed.Your computer may nothaveenough memory toopentheimage,or theimage may havebeen corrupted.Restartyour computer,and thenopen thefileagain. Ifthe red x stillappears,you may havetodelete theimageandthen insertitagain.
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?
8/8/2019 10. Antioxidants[1]
7/38
Preventive Antioxidants
Superoxide dismutase
Catalase
Glutathione peroxidase
Singlet oxygen quencher
Transition metal chelators (EDTA)
Preventive antioxidants minimize the formation of
initiating radicals
8/8/2019 10. Antioxidants[1]
8/38
Gluthione
HC
COOH
H
CH2
O C N C C N CH2COOH
CH2
CH2
NH2
H O H
SH
8/8/2019 10. Antioxidants[1]
9/38
8/8/2019 10. Antioxidants[1]
10/38
Radical Scavenging Antioxidant
Vitamin C
Tocopherol Quercetin
Anthocyanin
Radical scavenging antioxidants break free radical
chain reaction by donating hydrogen to free radicals
8/8/2019 10. Antioxidants[1]
11/38
Standard One-Electron Reduction PotentialCompounds Er (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
E- Tocopheroxyl H+ / E- Tocopherol 500
Ascorbate H+ / Ascorbate 282
8/8/2019 10. Antioxidants[1]
12/38
Resonance Stabilization of Antioxidant Radicals
OH
C(CH3)3
OCH3
C(CH3)3
OCH
3
O.
OCH
3
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)
+
8/8/2019 10. Antioxidants[1]
13/38
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.
8/8/2019 10. Antioxidants[1]
14/38
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
8/8/2019 10. Antioxidants[1]
15/38
Antioxidants
OH
C(CH3)3
OCH3
C(CH3)3(CH3)3C
CH3
OH
Butylated Hydroxy TolueneButylated Hydroxy Anisole
8/8/2019 10. Antioxidants[1]
16/38
OH
OHOH
COOC3H7
PropylGallate
OH
C(CH3
)3
OH
TBHQ
CH
CHO OH
OH
OH
CH3CH3
OH CHO
OH
CH
OH
CH3 CH3CH3 CH3
Gossypol
Antioxidants
8/8/2019 10. Antioxidants[1]
17/38
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).
8/8/2019 10. Antioxidants[1]
18/38
Reaction of antioxidants with radicalsRy + 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
y
y y
y
y
y y
y
yy
y
8/8/2019 10. Antioxidants[1]
19/38
Stable Resonance Formation of BHA
O H
C (C H3
)3
O C H3
Ry , RO y , orROO y
C (C H3
)3
O C H3
O
O C H3
C (C H3
)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
.
.
.
8/8/2019 10. Antioxidants[1]
20/38
O
C H3
H2
O H
C H3
C H3
H2
( C H2
)3
C H ( C H2
)3
C H ( C H2
)3
C H ( C H3
)2
C H3
C H3
E-tocopherol
O 2
C H3
C H 3
C H3
OC H 2
O
C H 2C ( C H 2 ) 3C H ( C H 2) 3C H ( C H 3) 2
C H3
C H3
C H3
O H
E- tocoquinone
Tocopherol and Oxygen Reaction
8/8/2019 10. Antioxidants[1]
21/38
Mechanisms of Metals in Accelerating Lipid Oxidation
Hydroperoxide decomposition to form peroxy or alkoxy radical.
Fe3+
+ ROOH Fe2+
+ ROO y + H+
Fe2+
+ ROOH Fe3+
+ ROy
+ OH-
Formations of alkyl free radical by direct reaction with fats and oils.
Fe3+
+ RH Fe2+
+ Ry + H+
Activation of molecular oxygen for singlet oxygen formation.
Fe2+
+ O2 Fe3+
+ O-
21O2
8/8/2019 10. Antioxidants[1]
22/38
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)
8/8/2019 10. Antioxidants[1]
23/38
O
M
C
O
CH2
O C
O
CH2
NCH2
CH2
O
O N
CO
CH2
C OCH2
Metal Ions EDTA Complex Formation
8/8/2019 10. Antioxidants[1]
24/38
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) otherphenolic antioxidants, or with (2) various metal
chelating agents.
8/8/2019 10. Antioxidants[1]
25/38
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 .
8/8/2019 10. Antioxidants[1]
26/38
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.
8/8/2019 10. Antioxidants[1]
27/38
8/8/2019 10. Antioxidants[1]
28/38
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.
8/8/2019 10. Antioxidants[1]
29/38
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
8/8/2019 10. Antioxidants[1]
30/38
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-availableEconomical
Not absorbable by the body
8/8/2019 10. Antioxidants[1]
31/38
Biochemical Control of Lipid Oxidation
8/8/2019 10. Antioxidants[1]
32/38
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%
8/8/2019 10. Antioxidants[1]
33/38
Glucose oxidase/catalase Reaction Mechanism.
Glucose oxidase/catalase reaction:
2 Glucose + 2O2 + 2H2O 2 Gluconic acid + 2H 2O2
2H2O2 2H2O + O2
The net chemical reaction is:
2 Glucose + O2 2 Gluconic acid
Glucose Oxidase
Catalase
Glucose Oxidase
Catalase
8/8/2019 10. Antioxidants[1]
34/38
8/8/2019 10. Antioxidants[1]
35/38
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)
8/8/2019 10. Antioxidants[1]
36/38
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 foodsCarry-through effect
Stability to pH and food processing
Availability
Cost
Non-adsorbable, if possible
8/8/2019 10. Antioxidants[1]
37/38
Antioxidants for Different Food Systems
A small surface-to-volume ratio PG and TBHQ
A large surface-to-volume ratio BHA and BHT
8/8/2019 10. Antioxidants[1]
38/38
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.
Top Related