Chemistry of Singlet Oxygen Oxidation of Foods

1
Chemistry of Singlet Oxygen Oxidation of Foods

• David B. Min
• Department of Food Science and Technology
• The Ohio State University
• Columbus, Ohio 43210

2
Oxidation of Foods

• Flavor Quality Consumer
  Acceptance
• Nutritional Quality Essential Fatty
  Acids
• Essential Amino Acids
• 
  Vitamins
• Health Risks Growth Retardation
• Heart
  Diseases
• 
  Carcinogens

3
Activation Energy for Food Chemical Reactions

Reactions
Activation Energy

(Kcal/Mole) Protein Denaturation
100 Nonenzymatic Browning
Reaction 50 Enzyme Catalyzed
Reaction 10-15 Singlet
Oxygen Oxidation 1-2
4
Oxygen History

• 1772 Scheele Priestley
• Discovered Oxygen
•  
• 1811 Avogadro
• Oxygen is a diatomic molecule
•  
• 1848 Faraday
• Oxygen is a paramagnetic molecule
•  
• 1934 Herzberg
• Discovered singlet oxygen
•  
• 1964 Foote Wexler
• Singlet oxygen in photooxidation
•  

5

• Mechanisms of Oxidation in Foods
• Triplet oxygen radical oxidation
• Singlet oxygen nonradical oxidation

6
Molecular Orbital of Triplet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
?
Energy
2S
2S
?
7
Reaction of 3O2 with Linoleic Acid
O
13 12 11 10 9
CH3 (CH2)3 -CH2 -CH CH-CH2 -CH CH-(CH2)7 -C-OH
_
H
O
CH3 (CH2)3 -CH2 -CH CH-CH CH-CH-(CH2)7 -C-OH

3O2
O
CH3 (CH2)3 -CH2 -CH CH-CHCH-CH-(CH2)7 -C-OH
O-O
H
CH3 (CH2)3 -CH2-CHCH-CHCH-CH-(CH2)7 -C-OH
O-O-H
8
Molecular Orbital of Singlet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
Energy
?
2S
2S
?
?
1S
1S
?
9
Singlet Oxygen Formation in Foods

Enzymes
RCOO RCOO
3O2 Sensitizer
Endoperoxides
H2O2 OCI-
Ozone
1O2
H2O2 O2 -
OH- O2 -
H2O2 HO2 -
O2 -
O2 - O2 -
O2 - Y
10
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
11
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
12
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
13
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14
Singlet Oxygen Formation by Sensitizer
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
15
ESR Singlet Oxygen Detection by Trapping Method
O
O
CH3
1O2
H3C
H3C
CH3
N
CH3
N
H3C
H3C
CH3
H
O
TMPD
TAN
16
Electron Spin Resonance Spectrum of 2,2,6,6-
Tetramethyl- 4 -Piperidone-N-Oxyl (TAN)
3370 G 3390 G
3410 G
17
Reaction of 1O2 with Linoleic Acid
OOH

1O
2
O
R
R
2
R
1
R
R
H
R
O
1
2
2
1
18
Effect of Chlorophyll on the Volatile Compounds
of Soybean Oil under Light at 10oC
Volatile Content (EU)
Storage in Hours
19
Carotenoids
C
H
O
Apo - 8'- carotenal
b -
b -
Carotene
O
Canthaxanthin
O
20
Diagram of Oxidized Compound Formation in Soybean
Oil by Chlorophyll Photosensitized Singlet Oxygen
ISC
3O2
A
Sen
1O2
A O2
1Sen
3Sen
Q
Q
Q
kq
kox-Q
Sen
O2
Q
3O2
dAO2
Ko3O2
k rA
K

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

21
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

22
Vitamin D Loss in Milk by Singlet Oxygen
Oxidation
23
Effects of Light Storage on the Vitamin D Loss
in Milk
Vitamin D Loss (ppm)
Vitamin D (ppm)
0 1 2 4 8 (hrs)
3000 0 280 426
558 795 6000 0
786 1188 1770 2712
9000 0 1476 2259
3492 5157
24
Mass Spectrum of Vitamin D2 Oxidation Product
25
Formation of 5,6 Diol of Vitamin D2
C
H
3
H
C
C
H
3
3
H
C
3
C
H
3
H
1O2
H
C
H
3
H
O
26
Sunlight Flavor Formation in Milk by Singlet
Oxygen Oxidation
27
Storage Time Effect on the Volatile Compounds of
Milk under Light
0 hour
D
4 hour
D
8 hour
D
28
Mass spectra of Peak D and Reference Dimethyl
Disulfide
Gas Chromatographic Peak D
Reference Dimethyl Disulfide
29
Effect of Ascorbic acid on Dimethyl Disulfide
Content in Milk
0 ppm Ascorbic Acid
Dimethyl Disulfide
200 ppm Ascorbic Acid
1000 ppm Ascorbic Acid
30
Mechanism of Dimethyl Disulfide Formation from
Methionine by Singlet Oxygen

C
O
H
O
O
O
C
O
O
H

N
H
C
H
C
H
C
H
S
C
H

1
N
H
C
H
C
H
C
H
S
C
H
2
2
3
O
2
2
2
3
2
2
O
C
O
O
H
O
O
H
C
O
O
H
N
H
C
H
C
H
C
H
S
C
H

N
H
C
H
C
H
C
H
S
C
H
O
H
2
2
3
2
2
3
O
C
O
O
H
C
O
O
H
N
H
C
H
C
H
C
H
S
C
H
N
H
C
H
C
H
C
H
O

S
C
H
2
2
3

2
2
3
2
C
H
S
S
C
H
S
C
H
3
3
3
31
Vitamin C and Riboflavin Losses in Milk by
Singlet Oxygen Oxidation
32
Loss () of Ascorbic Acid and Riboflavin in Milk
by Sunlight
Ascorbic acid Loss () Riboflavin Loss ()
Exposure (hours) Exposure (hours) 1 2
3 1 2 3
Unexposed 0 0 0 0 0 0 Carton 5.5
35.0 35.0 3.2 3.7
9.1 Brown Bottle 18.0 66.0 71.0
7.5 7.5 11.0 Clear Bottle
89.0 92.0 96.0 28.0
39.0 50.0
33
Singlet Oxygen Oxidation of Amino Acids
34
Singlet Oxygen Oxidation of Histidine Tryptophan
1O2
1O2
Foote, C.S, 1976, CRC Critical Rev.
35
Reversion Flavor Formation in Soybean Oil by
Singlet Oxygen
36
Effect of 0 and 5 ppm chlorophyll on the
Formation of 2-pentyl and 2-pentenyl furan of
Soybean Oil under light
0 ppm
             
     
     
trans-2-heptenal
5 ppm
2-pentylfuran
2-pentenlyfuran
37
Mass spectrum of 2-Pentenylfuran
38
Formation of 2-Pentenyl Furan from Linolenic Acid
C
H
C
H
C
H
(
C
H
)
C
O
O
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
2
2
6
3
2
2
2
1O2
C
H
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
3
2
2
6
2
2
O
O
H
C
H
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
2
6
2
3
2
2
O

1O2

O
H
39
Formation of 2-Pentenyl Furan from Linolenic Acid
Linolenic Acid
Singlet oxygen
C
H
(
C
H
)
C
H
C
C
H
C
H
C
C
H
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
2
2
3
2
3
2
2
2
2
2
O
O
O
O
C
H
C
H
C
H
C
C
H
C
H
(
C
H
)
C
H
C
H
C
C
H
C
H
C
H
3
2
2
2
O
H
O
H
O
H
O
H
C
H
C
H
C
H
C
H
C
H
C
H
(
C
H
)
C
H
C
H
2
2-(1-pentenyl)-furan
2-(2-pentenyl)-furan
3
2
3
2
2
O
O
40
Summary