Chemistry of Lipid Oxidation and Antioxidant

1
Chemistry of Lipid Oxidation and Antioxidant
David B. Min Department of Food Science and
Technology The Ohio State University
2
Effects of Lipid Oxidation

• Flavor Quality Consumer
  Acceptance
  
• Nutritional Quality Essential Fatty
  Acids
• Functional Quality Fats and Oils
• Health Risks Heart Disease
• Carcinogens

3
Activation Energy for Chemical Reaction

Reactions
Activation Energy

(Kcal/Mole) Nonenzymatic Browning Reaction
50 Enzyme Catalyzed Reaction
10-15 Oxidation of Food Lipids
10-15
4
1772 Scheele Priestley Discovered
Oxygen 1811 Avogadro Oxygen is a Diatomic
Molecule 1848 Faraday Oxygen is a
Paramagnetic Molecule 1934 Herzberg
Observation of Singlet Oxygen 1969 Foote
Wexler Rediscovered Singlet Oxygen  
               
Oxygen History
5
Lipid Oxidation Triplet oxygen free
radical oxidation Singlet oxygen oxidation
6
Molecular Orbital of Triplet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
?
Energy
2S
2S
?
7
Mechanism of Triplet Oxygen Oxidation
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
- ? H
Initiation
13 12 11 10 9
(
C
)
C
H
C
H
R
H
C
H
C
H
C
H
C
H
C
H
4
3
2
?
2
3O2
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
? H from RCOOH
O
?
8
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
Hydroperoxide Decompositin
O
- ? OH
H
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
?
C
H
(
C
H
)
C
HO
3
2
4
Termination
C
H
(
C
H
)
C
H
3
3
2
3
9
Molecular Orbital of Singlet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
Energy
?
2S
2S
?
?
1S
1S
?
10
Reaction of 3O2 and 1O2 with Linoleic Acid
.
OOH
3O
3O
2
2
R
R
2
R
1
R
R
2
R
1
2
1
OOH
1O
O
2
R
R
R
2
1
R
H
O
2
1
OOH
gtgtgt
1O
3O
2
2
R
R
2
1
11
Singlet Oxygen Formation in Foods

hn
3O2 Photosensitizer 1O2
12
Photosensitizers in Foods
? Chlorophyll ? Protoporphyrine ? Riboflavin
13
Chlorophyll
H
C
H
H
C
R
2
C
H
C
H
H
C
2
3
3
N
N
M
chl a, R -CH3
g
H
H
N
N
chl b, R - CHO
C
H
3
H
C
3
O
C
O
C
H
2
3
C
H
2

C
O
2
C
H
C
H
C
H
C
H
3
3
3
3
14
Excitation and Deactivation of Sensitizers
Excited State
1Sen
K1- 20?108/sec ISC
Fluorescence K 2?108/sec
3Sen
hv
K1- 3?109/sec
Phosphorescence
3O2
K10- 104/sec
1Sen (Chlorophyll)
Singlet Oxygen
Ground State
15
Singlet Oxygen Trapping
O
O
CH3
1O2
H3C
H3C
CH3
N
CH3
N
H3C
H3C
CH3
H
O
TMPD
TAN
16
ESR Spectrum of 2,2,6,6- Tetramethyl- 4
-Piperidone-N-Oxyl (TAN)
3370 G 3390 G
3410 G
17
Singlet Oxygen Oxidation of Soybean Oil
18
Soybean Oil Reversion Beany Flavor Compounds
C
H
C
H
C
H
C
H
C
H
2
3
2
O
2-(1-pentenyl)-furan
C
H
C
H
C
H
C
H
C
H
3
2
2
O
2-(2-pentenyl)-furan
19
Soybean Oil Purification by Chromatography
Soybean oil
Silicic acid
Sugar
Charcoal-Celite
Silicic acid
Vacuum
Purified soybean oil
20
Identified Compounds in Soybean Oil

• Phospholipids
• Tocopherols
• Monoglycerides
• Diglycerides
• Oxidized triglycerides
• Free fatty acids
• Chlorophylls

21
Purified Soybean Oils
22
Light Box for Soybean Oil Flavor Study
23
Effect of 0 and 5 ppm Chlorophyll on
2-Pentenylfurans in Soybean Oil
0 ppm
             
     
No beany flavor
5 ppm
trans-2-heptenal

2-pentenylfuran
Strong beany flavor
24
Mass Spectrum of 2-Pentenylfuran
25
Reversion Beany Flavor from Linolenic Acid by
1O2
1O2
C
H
C
H
C
O
O
H
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
2
6
2
3
2
2
O
O


C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
3
2
2
1O2
O
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
3
2
2
O
O
O
26
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
3
2
2

O
O
O
H
- OH

C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
3
2
2

O
O

C
H
C
H
C
H
C
H
C
H
C
C
H
C
H
C
H
3
2
2
2
2
O
O
C
H
C
H
C
H
C
H
C
H
C
C
H
C
H
C
H
3
2
2
O
H
O
H
- H2O
2-(2-pentenyl)-furan
C
H
C
H
C
H
C
H
C
H
3
2
2
O
27
Chlorophyll Effect on the Headspace Volatile
Compounds of Soybean Oil under Light at 10 oC
Headspace Volatile Content (electronic
unit)
Storage in Hours
28
Carotenoids
C
H
O
O
Canthaxanthin
O
29
Effects of ?-Apo-8-Carotenal, ?-Carotene or
Canthaxanthin on Soybean Oil Oxidation
Peroxide Value (meq/kg oil)
Storage Time (hr)
30
Effects of ?-Apo-8-Carotenal, ?-Carotene or
Canthaxanthin on Soybean Oil Oxidation
Peroxide Value (meq/kg oil)
Storage Time (hr)
31
Schematic Diagram for the Formation of Product AO2
Carotenoids
A
3O2
ISC
Sen
1O2
1Sen
A O2
3Sen
(Chlorophyll)
Q
Q
kq
Sen
kq
kox-Q
Sen
3O2
3O2
O2
Q
dAO2
Ko3O2
k rA
K

Ko3O2kQQ
k rA (kox-Q kq)Q kd
dt

32
Steady State Kinetic Equation
If carotenoids quenched singlet oxygen , steady
state kinetic equation
dAO2
Ko3O2
k rA
K

Ko3O2kQQ
k rA (kox-Q kq)Q kd
dt

If carotenoids quenched triplet chlorophyll ,
steady state kinetic equation
dAO2
Ko3O2
k rA
K

Ko3O2kQQ
k rA (kox-Q kq)Q kd
dt

33
Quenching Mechanism of b-Carotene
1/ Peroxide Value ( 1/ M )
34
Total Quenching Rate Constant (KqKox-Q) of
Singlet Oxygen by Carotenoids
Carotenoids Number of Conjugated
Quenching Rate Double Bonds
Constants ( M-1 sec-1) ?
-apo-8- Carotenal 10
2.86 ? 109 ? -
Carotene 11
4.60 ?
109 Canthaxanthin 13
1.12 ?
1010

35
Singlet Oxygen Quenching Mechanism of Carotenoid
1O2 1?-Carotene 3O2 3?-Carotene
3 ?-Carotene
1?-Carotene
Energy Transfer
Radiationless Transfer
36
Antioxidants
37
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
38
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
(K 10o M-1sec-1) ? H from RH (triglyceride)
Propagation
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
39
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
40
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
41
Preventive Antioxidants

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

42
Radical Scavenging Antioxidant

• Vitamin C
• Tocopherol
• Quercetin
• Anthocyanin
• Radical scavenging antioxidants break free
  radical chain reaction by donating hydrogen to
  free radicals

43
Standard One-Electron Reduction Potential
Compounds E? (mV)
HO H / H2O 2310 RO H /
ROH 1600 ROO H / ROOH 1000 R H /
RH 600 Catechol H / Catechol 530 ?-
Tocopheroxyl H / ?- Tocopherol 500 Ascorbate
H / Ascorbate 282

44
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
45
Ascorbic Acid

• Hydrogen donation to radicals
• Quenching of singlet oxygen
• Regenerate tocopherol from tocopheryl radicals
• Prooxidant Reduce weak catalyst ferric
  iron
• to strong catalyst ferrous iron in aqueous
  system

46
Food Antioxidants as Multifunctionals

• Free radical scavenger
• Reactive oxygen scavenger
• Metal chelators
• Regenerators for other antioxidant radicals

47
Food Solvent Effects on Antioxidants

• Nonpolar solvent (nonhydrogen bond)
• LOO. HOAr LOO. . HOAr LOOH .
  .OAr
• LOOH ArO.
• Polar solvent (hydrogen bond)
• LOO. ArOH LOO- . .HOAr LOO-
  H ArO.

48
Rate Constant of a-Tochopherol with Peroxyl
Radical

• Medium K (M-1s-1)
• Lipid 7 x 106
• Water 8 x 105
• Phospholipid bilayer 3 x 103

Trolox
49
Summary