Mechanisms and Control of Oxidation of Foods

1
Mechanisms and Control of Oxidation of Foods
DAVID B. MIN DEPARTMENT of FOOD SCIENCE and
TECHNOLOGY THE OHIO STATE UNIVERSITY
2
Oxidation Effects of Foods
? Flavor Quality Consumer
Acceptance
? Nutritional Quality Essential Fatty
Acids
Vitamins ? Functional Quality Proteins and
Lipids ? Health Risks Growth Retardation
Heart
Diseases
Enlargement of Kidney
Carcinogens
3
Activation Energy for Chemical Reaction

Reactions
Activation Energy

(Kcal/Mole) Protein Denaturation
100 Nonenzymatic Browning
Reaction 50 Enzyme Catalyzed
Reaction
10-15 Oxidation of Food Components
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
Oxidation of Food Components Triplet
oxygen free radical oxidation Singlet
oxygen oxidation
6
Triplet Oxygen Oxidation
7
Molecular Orbital of Triplet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
?
Energy
2S
2S
?
8
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
INITIATION
- ? 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
?
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
O
PROPAGATION
? H
?
9
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 DECOMPOSION
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
?
12 11 10 9
O
?
C
C
H
C
H
C
H
C
H
C
H
R

C
C
H
(
C
H
)
H
2
3
2
3
2
H
TERMINATION
? H
C
H
(
C
H
)
C
H
3
2
3
3
10
Mechanism of Lipoxygenase in Linolenic Acid
H
H
H
H
H
H
cis
cis
cis
H
C
C
C
C
C
C
H
C
C
CH
H
(CH
)
(
C
H
)
C
O
O
H
2
4
3
.
2
6
H
- H
H
H
H
H
H
cis
H
cis
cis
H
C
C
C
C
C
C
H
C
.
C
CH
(CH
)
H
(
C
H
)
3
2
4
C
O
O
H
2
6
H
H
H
H
cis
cis
H
trans
H
C
C
C
C
H
C
C
C
H
(
C
H
)
.
C
O
O
H
(CH
)
CH
C
2
4
3
2
6
H
3

O
2
H
H
H
H
cis
cis
H
H
C
trans
C
C
C
C
C
C
H
(
C
H
)
C
O
O
H
2
6
CH
(CH
)
C
3
H
2
4
O
O
H
11
Protein Oxidation

• Oxidation of amino acid side chains
• Protein-protein cross linkage
• Protein fragmentation
• Volatile compound formation

12
Protein Oxidation
Protein cross linkage
R
O
R
O
R
O
P
P
P
P
P
P
N
C
C
N
C
C
N
C
C

O2

H
H
H
H
O
O
H
R
O
- OH
R
O
R
O
H
P
P
P
P
P
P
N
C
C
N
C
C
N
C
C
H
O
H
H
O

H
O
O
H
Peptide bond cleavage
13
Peptide Bond Cleavage
H
O
O
H
O

P
C
C
N
H
C
P
Diamide pathway
C
C
N
C
O
R
R
R
1
2
3

H
O
O
O
H
O
P
P
C
C
N
H
C
C
N
H
C
C
R
R
R
1
2
3
H
O
O
O
H
O

?-amidation pathway
P
P
C
C
N
H
C
C
C
C
N
H
2
R
R
R
2
3
1
14
Protein Carbonyl Formation from Aldehydes
4-Hydroxy-2-nonenal from lipid oxidation
O
H
O
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
S
P
Protein-cystein -SH
O
H
O
O
H
O
P-lysine -NH2
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
C
H
H
3
2
2
2
2
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
3
2
2
2
2
H
N
P
Protein-histidine
O
H
O
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
2
N
N
P
15
Protein Carbonyl Formation from Aldehydes
Malonaldehyde from lipid oxidation react with
protein amino groups (PNH2)
C
H
N
H
P
C
H
N
P
C
H
N
P
C
H
O
C
H
C
H
C
H

2
C
H
2
C
H
O
C
H
O
C
H
O
H
C
H
O
16
Formation of Protein Carbonyls from Sugars
Glycation and glycoxidation of sugars and protein
lysyl amino groups produce protein carbonyls.
C
P
N
H
C
N
P
C
O
(
H
C
O
H
)
n
C
O
H
)
n-1
(
H
C
H
O
R

R
(
H
C
O
H
)
n
P
N
H
2
Lysine
R
C
H
N
P
C
H
O
O2
P
N
H
C
O
C
O
2
C
O
H
)
n-1
(
H
C
O
H
)
n-1
(
H
R
R
17
Singlet Oxygen Oxidation
18
Molecular Orbital of Singlet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
Energy
?
2S
2S
?
?
1S
1S
?
19
Comparison of 3O2 and 1O2

3O2 1O2 ENERGY LEVEL
0 22.5 Kcal
NATURE DIRADICAL NO
RADICAL REACTION RADICAL
ELECTRON-RICH

20
Singlet Oxygen Formation

Enzymes
RCOO RCOO
3O2 Sensitizer
Endoperoxides
H2O2 OCI-
Ozone
1O2
H2O2 O2 -
OH- O2 -
H2O2 HO2 -
O2 -
O2 - O2 -
O2 - Y
21
Photosensitizers in Foods
? Chlorophyll ? Protoporphyrine of Myoglobin ?
Riboflavin ? Red No. 3
22
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
23
Riboflavin
C
O
H
H
2
C
H
O
H
C
H
O
H
C
H
O
H
C
H
2
C
H
N
N
O
3
N
H
N
C
H
3
O
24
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
Singlet Oxygen
Ground State
25
Singlet Oxygen Trapping
O
O
CH3
1O2
H3C
H3C
CH3
N
CH3
N
H3C
H3C
CH3
H
O
TMPD
TAN
26
Electron Spin Resonance Spectrum of 2,2,6,6-
Tetramethyl- 4 -Piperidone-N-Oxyl (TAN)
3370 G 3390 G
3410 G
27
Reaction of 3O2 and 1O2 with Linoleic Acid
OOH
.
3O
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
28
Singlet Oxygen Oxidation in Foods
29
Singlet Oxygen Oxidation of Protein
30
Sulfide Compounds Formation from Protein
O
O
-
-
Protein

C
H
C
H
S
C
H

Protein
1
C
H
C
H
S
C
H

2
3
O
2
2
3
2
2
O
O
O
H
-
Protein
Protein-
C
H
C
H
S
C
H

C
H
C
H
S
C
H
O
H
2
3
2
3
O
Protein-
Protein-
C
H
C
H
S
C
H

C
H
C
H
O

S
C
H
2
3
2
3
2
C
H
S
S
C
H
S
C
H
3
3
3
Disproportionation
2
S
C
H
S
S
C
H

C
C
H
S
C
H
C
H
S
S
H
3
3
3
3
3
3
31
H2S Formation from Protein
O
O

-
-

Protein
1
C
H
S
H
Protein
C
H
S
H
O
2
2
2
O
O
O
H


-
-

Protein
H
H
C
H
S
H
Protein
S
O
H
C
H2S2
-
O
( )
2

Protein
H
C
S
H
S
H
Disproportionation
2H2S2
2H2S S2
32
Protein Histidine Tryptophane
1O2
Protein
-
C
H
N
2
Protein
-
C2N2H3
C
H
C
O
O
H
2
N
H
Protein
CH2-COHNCNH2CO
Protein
-
C
H
Protein
-
2
C
H
1O2
2
O
N
C
H
O
N
H
H
Foote, C.S, CRC Critical Rev.
33
Singlet Oxygen Oxidation of Soy Protein
Concentrate  
Volatile compounds in soy protein concentrate
under light and dark at 30?C for 6 days were
studied by a combination of solid phase
microextraction -gas chromatography-mass
spectrometry and sensory evaluation.
34
Volatile Compounds Formation at 30º C for 6 Days
Dark Storage 60 Increased Light Storage 300
Increased and 1-Pentanol, 2-heptenal, and
2-pentyl furan by singlet oxygen oxidation
35
Singlet Oxygen Oxidation of Soybean Oil
36
Reversion Flavor Compounds from Soybean Oil
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
3
2
2
O
O
2-(2-pentenyl)-furan
2-(1-pentenyl)-furan
37
Reversion Flavor from Linolenic Acid by Singlet
Oxygen Oxidation
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
38
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
39
Singlet Oxygen Oxidation of Vitamin D
40
Mass Spectrum of Vitamin D2 1O2 Oxidation
Product
41
Singlet Oxygen Oxidation of Vitamin D
C
H
3
H
C
C
H
3
3
H
C
3
C
H
3
303
O
H
H
H
O
H
C
H
3
O
H
C
H
3
H
O
128
H
O
5,6 Diol of Vitamin D2
42
Headspace Oxygen Determination by Gas
Chromatography
Headspace Analysis Sample Bottle
43
Light Storage Box of Samples
44
Chlorophyll Effect on the Headspace Volatile
Compounds of Soybean Oil under Light at 10 oC
Headspace Volatile Content (electronic
unit)
Storage in Hours
45
Carotenoids
C
H
O
O
Canthaxanthin
O
46
Effects of ?-Apo-8-Carotenal, ?-Carotene or
Canthaxanthin on Soybean Oil Oxidation
Peroxide Value (meq/kg oil)
Storage Time (hr)
47
Schematic Diagram for the Formation of Product AO2
ISC
3O2
A
Sen
1O2
1Sen
A O2
3Sen
kd
Q
Q
Sen
kq
kox-Q
Sen
3O2
3O2
Q
O2
dAO2
Ko3O2
k rA
K

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

Singlet Oxygen Oxidation Quenching Mechanism of
Caroteinoids by Steady State Kinetic Equation
48
Singlet Oxygen Quenching
-1
K
Slope
Q4
?
?
1/AO2
Q3
Intercept K-1
?
?
?
?
Q2
?
?
1 K
?
Q1
?
?
?
1/A
49
Quenching Mechanism of b-Carotenene
1/ Peroxide Value ( 1/ M )
50
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

51
Singlet Oxygen Quenching Mechanism of Carotenoid
1O2 1?-Carotene 3O2 3?-Carotene
3 ?-Carotene
1?-Carotene
Energy Transfer
Radiationless Transfer
52
Let us stand up and stretch
53
Antioxidants
54
Characteristics of Free Radicals in Oxidation
-
O2 Superoxide anion An oxygen-centered
radical. Limited reactivity HO
Hydroxyl A highly reactive oxygen-centered
radical. Indeed attacks all molecules in
human body RO2 Peroxyl Oxygencentered
radicals formed during the RO Alkoxy
breakdown of organic peroxides
55
Linoleic Acid Oxidation by Triplet Oxygen
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
- H
R (CH2)6-COOH

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
2
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
O
PROPAGATION

H

56
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
O
- OH

DECOMPOSION
H
12 11 10 9
C
H
R
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
2
2
4
3
O

O

C
C
H
C
H
C
H
C
H
C
H
R
C
H
(
C
H
)
C
H

2
3
2
3
2
H
TERMINATION
H

C
H
(
C
H
)
C
H
(PENTANE)
3
2
3
3
R (CH2)6-COOH
57
.
R, RO, ROO, O-2 1O2, -OH, H2O2,Cu, Fe
Antioxidants
Prooxidant Jail
R, RO, ROO, 1O2, O-2, -OH, H2O2, Cu, Fe
58
Functions of Antioxidant on Food Oxidation

• Inhibits or slows the free alkyl radical
• formation in the initiation step
• Interrupts the propagation of free radical chain
  
• Slows the free radical chain reaction rate of
• food oxidation.

59
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

60
Characteristics of Hydrogen Donating Antioxidants
The major hydrogen donating antioxidants are
monohydroxy or polyhydroxy phenolic compounds
with various ring substitutions. The
antioxidant free radical does not initiate
another free radical due to the delocalized
stabilization of radical electron.
61
Effectiveness of Antioxidants

• The difference of one-electron reduction
• potential.
• The stability of antioxidant radicals
• by resonance stabilization of radical
  electron.
• Antioxidant radicals should not initiate
• another food free radicals.

62
Resonance of Antioxidant Radicals
O
H
C
(
C
H
)
3
3
O
C
H
3
RH , ROH , ROOH
R , RO , ROO



.
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
3
.
O
C
H
O
C
H
3
3
63
Targets of Antioxidant

• Antioxidants can react with peroxyl
  radicals rather than alkoxyl radicals.
• The most prevalent radical is peroxyl (ROO)
  radical.
• Peroxyl radical has the lower standard one
  electron reduction potential than alkyl or
  alkoxyl radical

64
Synthetic Antioxidants
Butylatedhydroxyanisole (BHA)
Butylatedhydroxytoluene (BHT)
Tertiary butylhydroquionone (TBHQ)
Propyl gallate
65
Natural Antioxidants

• Benefits
• Health implication
• Stability in food system
• Limits
• Characteristic flavor
• Safety test required

66
Tocopherols
R
1
H
O
C
H
C
H
C
H
C
H
3
3
3
3
R
O
2
R
3
Tochperols R1 R2 R3 ?-Tocopherol CH3 CH3 CH3
?-Tocopherol CH3 H CH3 ?-Tocopherol H CH3 CH3
d-Tocopherol H H CH3
67
Antioxidant Mechanism of Tocopherol

• Transfer of phenolic hydrogen
• Scavenging of singlet oxygen

68
Ascorbic Acid

• Hydrogen donation to radicals
• Quenching of singlet oxygen
• Removal of molecular oxygen
• Regenerate tocopherol from tocopherol radicals
• Prooxidant Reduce ferric iron to ferrous
  iron

69
Ascorbic Acid
C
H
O
H
C
H
O
H
2
C
H
O
H
2
2
H
C
O
H
H
C
O
H
H
C
O
H
O
O
O
O
O
O
- H
- H
H
H
H

O
O
H
O
H
O
O
O
H
L-Ascorbic acid
Dehydroascorbic acid
70
Ascorbic Acid and Related Compounds
O
C
H
O
H
2
C
H
O
H
C
H
O
C
(
C
H
)
C
H
2
2
2
14
3
H
C
O
H
H
O
H
C
C
H
O
H
O
O
O
O
O
O
H
H
H
H
O
O
H
O
H
H
O
H
O
O
H
L-Ascorbic Acid
Erythorbic Acid
Ascorbic Palmitate
71
Ascorbic acid can act as a prooxidant by reducing
ferric to ferrous ion, which become more active
catalysts of oxidation in the aqueous system.
72
Synergistic Effect of Tocopherol Ascorbic Acid
Lipid peroxyradical
gt
H
Lipid hydroperoxide
?-Tocopheryl radical ?
?-Tocopherol
Ascorbic acid
lt
- H
Dehydroascorbic acid
73
Antioxidant Sources
74
Flavonoids
O
H
O
H
O
H
O
O
H
O
H
O
O
H
O
H
O
G
l
u
c
os
i
de
O
O
H
O
H
Quercetin Flavonols
Cyanidin-3-glucoside Anthocyanins
75
Flavonoids

• Secondary products of plant metabolism
• Hydrogen donor to radical compounds
• Metal chelating ability
• Superoxide anion scavengers
• Anthocyanines, catechins, flavones, flavonols,
  isoflavone, and proanthocyanidins

76
Vegetables
Cacao beans, Potato, Tomato, Spinach, Legumes,
Garlic, and Seaweed Polyphenolic compounds
77
Fruits and Red Wine
Polyphenolic compounds
78
Tea
O
H
O
H
O
H
O
H
O
O
O
H
H
O
O
H
O
H
O
H
O
H
O
H
Epigallocatechin
Epicatechin
79
Sesame Seed
O
O
O
O
O
O
O
O
H
O
H
O
C
H
3
Sesamol
Sesamolinol
80
Herb and Spice
Sage, Ginger, Green pepper, Lavender and Rosemary

O
H
C
H
3
H
O
O
C
H
3
C
O
C
H
H
C
3
3
Carnosoic Acid
Carnosol
O
H
H
O
O
C
O
H
O
O
H
O
Rosemarinic Acid
O
H
81
Reaction Rates of Carnosol and Carnosic Acid
Carnosic acid

O
H
O
H
O
H
O
H
O
O
C
H
O
O
C


LOO
LOOH
3 ? 107 M-1s-1
H
H
Carnosol

O
H
O
H
O
H
O


O
O
LOO
LOOH
C
C
2 ? 106 M-1s-1
O
O
H
H
82
Soybean

• Chlorogenic acid, caffeic acid, ferulic acid -
• Metal chelation and singlet oxygen quenching
• Isoflavones - phytoestrogen effects -
• Metal chelation and hydrogen donation

83
Soybean
C
O
O
H
H
O
R
O
2
H
O
O
O
H
1
O
H
O
H
Isoflavones
Chlorogenic acid
R1 R2
Genistein OH OH Daidzein H OH
84
Ginseng

85
Ginseng
C
H
C
H
C
O
O
H
C
H
C
H
C
O
O
H
H
O
H
O
O
H
O
C
H
3
Caffeic acid
Ferulic acid
O
O
H
C
O
O
H
O
H
O
H
H
O
O
H
O
O
C
H
3
Vanillic acid
Kaempferol
86
Ginseng
Singlet oxygen quenchers Caffeic acidgt
Kaempferol gt Vanillic acid gt Salicylic acid gt
Ferulic acid Hydrogen donation to radicals
Kaempferol gt Maltol gt Vanillic acid gt Saponin gt
Salicylic acid gt Ferulic acid Metal chelation
activity Kaempferol gt Maltol gt Vanillic acid gt
Ferulic acid gt Caffeic acid
87
Maillard Reaction
Reducing Sugars and ?-amino acids
N-glycosylamine or N-fructosylamine
1-Amino-1-deoxy-2-ketose (Amadori intermediate)
or 2-Amino-2-deoxy-1-aldose (Heynes intermediate)
Reductones and dehydroreductones
H2S NH3
Strecker degradation
Amino Acids
Retroaldol condensation
Furans Thiophenes Pyrroles
Hydroxyacetone Hydroxyacetylaldehyde Acetoin Acet
ylaldehyde
Glyoxal Pyruvaldehyde Glycerolaldehyde
Aldehydes ?-aminoketone
(Methional, NH3, H2S)
Heterocyclizaion
Pyrazines Pyridines Oxazoles
Thiazoles Pyrroles
88
Antioxidants from Maillard Browning
C
H
3
C
O
Nitrogeneous compounds
C
O
H
C
O
H
C
H
O
H
C
H
S
H
C
H
3
2
C
H
O
H
Ethyl thiol
C
H
O
H
2
Reductone
89
Consideration of Antioxidant Selection
90
Ideal Antioxidants
 

• No harmful physiological effects
• No pathological effect
• No carcinogenic potential
• No interactions with enzymes
• No effects of reproduction
• No metabolism rate effect

91

• No objectionable flavor, odor, or color
• Effective in low concentration
• Fat-soluble
• Carry-through effect
• Readily-available
• Economical
• Not absorbable by the body

92
Thank you
93
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94
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95
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96
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97
Multifunctional Antioxidants

• Tocopherol
• Ascorbic acid

98
Antioxidant Interactions

• Combination of metal chelator and free radical
• scavenging antioxidants
• Combination of different antioxidants like
• ?- tocopherol and ascorbic acid

99
Types of Antioxidants

• Hydrogen donating compounds
• Singlet oxygen quenchers
• Metal chelators
• Antioxidant enzymes
• Oxygen scavengers and reducing agents

100
Metal Chelators
101
Prooxidant Mechanisms of Metals
k1
Fe3 ROOH Fe2 ROO H Fe2 ROOH Fe3
RO .OH Formations of alkyl free
radical by direct reaction Fe3 RH Fe2
R H Activation of oxygen for
singlet oxygen formation Fe2 3O2 Fe3
O-2 1O2 Formation of hydroxyl
radical Fe2 H2O2 Fe3 OH- OH

k2

k2 ? k1 105


.

102
Reaction between Metal and Hydroperoxide

• Rapid Exponential increase in oxidation during
  propagation step
• Scission of alkoxyl radical to low molecular
  weight compounds
• Copper is 50 faster than ferrous ion in
  decomposing hydrogen peroxide
• Ferrous is 105 faster than ferric iron in
  decomposing hydrogen peroxide
• Ferrous is 1015 times more soluble than ferric
  iron

103
Metal Chelators

• Phosphoric acid
• Citric acid
• Ascorbic acid
• Ethylene Diamine Tetra Acetate (EDTA)
• Proteins such as transferrin, ovotransferrin
• Amino acids

104
Mechanism of Metal Chelators

• Chelators form complex ions or coordination
  compounds with metals
• Prevention of metal redox cycling
• Occupation of all metal coordination sites
• Formation of insoluble metal complexes
• Steric hindrance of interactions between metals
  and lipid intermediates

105
Phospholipids
O
O
C
H
O
C
R
O
2
1
C
H
O
C
R
O
2
1
C
H
O
C
R
O
2
C
H
O
C
R
O
2
-
C
H
O
P
O
C
H
C
H
N
H
2
2
2
2
C
H
O
P
O
-
2
-
O
O
Phosphatidyl ethanolamine
Phosphatic acid
106
Interaction of Chealator and Metal
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
Ethylene Diamine Tetra Acetate
107
Oxygen Scavengers
108
Oxygen Scavengers and Reducing Agents

• Ascorbic acid
• Ascorbic palmitate
• Erythorbic acid
• Sodium erythorbate
• Sulfites

109
Oxygen Scavenger Mechanisms
C
H
O
H
2
H
C
O
H
O
O
½ O

H O

2
H
2
O
O
C
H
S
H
C
H
S
S
C
H
½ O
H O


2
2
3
3
3
O
O
O
O
H
H
O
S
2
H
O
S
O
H
O
110
Superoxide Dismutase

• Producing triplet oxygen from superoxide anion

-
.
Superoxide Dismutase


2O
O

2H
3
H
O
2
2
2
2
Catalase
2H
O
3

O
O
2H
2
2
2
2
111
Types of Antioxidants

• Hydrogen donating compounds
• Singlet oxygen quenchers
• Metal chelators
• Antioxidant enzymes
• Oxygen scavengers and reducing agents

112
Types of Antioxidants

• Hydrogen donating compounds
• Singlet oxygen quenchers
• Metal chelators
• Antioxidant enzymes
• Oxygen scavengers and reducing agents

113
Amino Acid, Peptide and Protein

• Glycine, methionine, and lysine in emulsion
• system- antioxidant activity at low
  concentration
• and high pH.
• Carnosine inhibits the activities of hemoglobin,
• lipoxygenase, iron, peroxyl, and hydroxyl
  radical.
• Ferritin and tranferritin proteins bind iron

114
Polarity of Antioxidants

• Polar antioxidants are more active in bulk oil
• systems
• Hydrophobic antioxidants that are located on
• the interface of lipid/water can protect lipid
• better than hydrophilic antioxidants

115
Concentrations

• Compare antioxidants at the same molar
• concentration of active components using
• structurally related reference compounds.
• Consider the concentration ratios of
• catalytic inducers/antioxidants and
• antioxidants/substrates.

116
Effects of Antioxidant Polarity in Food Systems
Oil
Water
Air
Water
Oil
Oil
Hydrophobic antioxidant
Hydrophilic antioxidant
117
Factors Affecting Partitioning of Antioxidants

• The chemical structure and polarity
• The types of lipid substrate
• The presence of surfactants
• pH
• The composition of the phases

118
Possible Future Antioxidants
Antioxidant attached to the packaging materials
119
Effects of Protein Oxidation

• Alteration of signal transduction mechanisms
• Transport systems
• Enzyme activities
• Atherosclerosis
• Ischemia-reperfusion injury
• Aging

120
Biomarkers of Protein Oxidation

• Protein carbonyls
• Stable amino acid modification
• Protein products of glycation and glycoxidation

121
Carotenoids
122
Singlet Oxygen Quenching Constant of Carotenoids
Carotenoids Number of Conjugated
Rate Constants
Double Bonds (109 M-1
sec-1) Astaxanthin 13
9.88 Isozeaxanthin
11
7.31 Zeaxanthin 11
7.03 Lycopene
11
6.89 Lutein 10
5.86
123
Vitamin D2
124
Effect of Vitamin D Concentration on Headspace
Oxygen Loss with 15 ppm Riboflavin
Headspace Oxygen Loss?
Vitamin D (ppm)
0 1 2 4 8 (hrs)
3000 0 9.3aa 14.2ab
18.6ac 26.5ad 6000 0
13.1ba 19.8bb 29.5bc 45.2bd
9000 0 16.4ca
25.1cb 38.8cc 57.3cd
? yellow and white are significant change with
time and vitamin D at plt0.05
125
2,2-Thiobis-1,1,3,3-tetramethyl-phenalto
-butylamine nickel
126
Effects of bis(di-n-butyldithiocarbamato) nickel
on the headspace oxygen of soyoil containing 3
ppm chlorophyll for 2 hrs
1/ Headspace Oxygen Depletion (ml headspace /
?moles O2)
1/ Oil in Methylene Chloride (1/ M)
127
BTC

Intercept Kd/Kr Kd 1.1 ? 104 sec -1 in
methylene chloride Kr 1.38 ? 105 (M-1 sec -1
) Slope Kq Kox-Q/Kr Kq Kox-Q 1.23 ? 109
M-1 sec -1
128
Purification of Soybean Oil
Soybean oil
Silicic acid
Sugar-celite
Charcoal-celite
Silicic acid
Vacuum
Purified soybean oil
129
Triplet Sensitizer Quenching
Q3
Q2

?

1/ AO2
Q1
?
?

?
?
?

Slope K-1kd(ko3O2 kQQ) /
ko3O2kr Intercept K-1(ko3O2 kQQ) /
ko3O2
?
1/A
130
Triplet Sensitizer Quenching Mechanism
-1
dAO2
k rA (kox-Q kq)Q kd
-1
Ko3O2kQQ
K
Ko3O2
k rA
dt

If there is only triplet sensitizer quenching,
the equation is
-1
dAO2
-1
K
k rA
dt
Plot of AO2 -1 vs. A -1 at various Q
131
Fragmentation Scheme for 5,6 Epoxide of Vitamin D2
132
Singlet Oxygen Quenching Mechanism
-1
dAO2
k rA (kox-Q kq)Q kd
-1
Ko3O2kQQ
K
Ko3O2
k rA
dt
If there is only singlet oxygen quenching, the
equation is

K
Plot of AO2 -1 vs. A -1 at various Q
133
Effect of Vitamin C on the Headspace Oxygen of
Vitamin D2
1/ Headspace Oxygen Depletion (ml headspace/
?moles O2)
1/ Vitamin D2 (1/M)
134
Determination of Ascorbic Acid Reaction Rate with
Singlet Oxygen
Slope / Intercept 8.1 ?10- 4 M
Kd 2.5 ?10 5 Sec-1 (in water) Kr 3.08 ?10 8
M-1 Sec-1
135
Effects of a-, ?-, or ? - tocopherol on the
peroxide of soy oil containing 3 ppm chlorophyll
during light storage
Peroxide Value (meq/kg oil)
Storage time (hrs)
136
Effects of a-tocopherol on the oxidation of
soyoil containing 3 ppm chlorophyll
1/ Peroxide (1/ M)
1/ Soybean Oil (1/ M)
137
? - Tocopherol
Intercept Kd/Kr Kd 1.1 ? 104 sec -1 in
methylene chloride Kr 1.04 ? 105 (M-1 sec -1
) Slope Kq Kox-Q/Kr Kq Kox-Q 2.7 ? 107
M-1 sec -1
138
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139
Protoporphyrin
C
C
H
C
H
C
C
H
3
2
C
C


C
H
HC
N
C
C
H
C
C
C
H
C
3
3
N
Fe
N
C
H
C
C
C
H
C
C
2
N
H
O
O
C
C
H
C
H
2
2
C
H
C
C
H
C
C
C
C
H
H
O
O
C
C
H
C
H
3
2
2
140

• Oxidization of histidine to 2-oxohistidine in
• the metal binding site of proteins.
• Oxidation of thiol groups and in particular the
• generation of carbonyl derivatives of amino
  acids

141
Reaction of Antioxidants with Radicals
R AH RH A
RO AH ROH A
ROO AH ROOH A
142
Reaction of Antioxidants with Radicals






143
Stability of Antioxidant Radical

O
C
H
3
C
C
H
3
C
H
3
O
C
H
3
144
Tocopherol
A chain breaking antioxidant competes with
polyunsaturated lipid for the lipid peroxyl
radicals.
?-Tocopherol ?-Tocopheryl semiquinone ?
Lipid radicals
Lipid radicals
?-Tocopheryl quinone
145
Enzymatic Antioxidants
146
Glucose Oxidase/Catalase
Glucose Oxidase
2 Glucose 2O2 2H2O 2 Gluconic acid
2H2O2
Catalase
2H2O2 2H2O O2
Glucose Oxidase Catalase
2 Glucose O2 2 Gluconic acid
Oxygen Scavenging
     


147
Superoxide Dismutase

• Superoxide anion participates in oxidative
  reactions
• Maintaining transition metals in their reduced,
  active state
• Promoting the release of metals bound to
  proteins
• Producing singlet oxygen

Superoxide Dismutase
-
3
O


2O

2H
2
2
2H
O
Catalase

O
2H
O
2
2
2
2
148
Glutathione Peroxidase
H2O2 2GSH 2H2O GSSG LOOH
2GSH LOH H2O GSSG
GSH Reduced glutathione GSSH Oxidized
glutathione