Chemistry and Reactions of Reactive Oxygen Species in Foods

1
Chemistry and Reactions of Reactive Oxygen
Species in Foods

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

2
Introduction

• Reactions of ROS with food components produce
  undesirable volatile compounds, carcinogens,
  destroy essential nutrients, and change the
  functionalities of proteins, lipids and
  carbohydrates.

3
Introduction

• The reactive oxygen species is a collective term
  to include oxygen radicals and non radical
  derivatives of oxygen. They are HO., RO., HOO.,
  ROO., O.-, 1O2, O3, and . H2O2.
• ROS is formed enzymatically, chemically,
  photochemically and by irradiation of food. They
  are also formed by the decomposition and the
  inter-reactions of ROS.
• Hydroxy radical is the most reactive ROS and
  then singlet oxygen.

4
Reactive Oxygen Species Formation in Foods
5
Superoxide Anion
6
Superoxide Anion

• Xanthine H2O 2O2
  Uric acid 2O2 2H
• NADPH 2O2 NADP
  2O2 H

Xanthine oxidase
NADPH Oxidase
7
Superoxide Anion

• X-NN-Y X N2 Y
• (Azo dyes in foods)
• X O2 X
  O2
• Y O2 Y
  O2

8
Superoxide Anion

• 1 TPR light 1 TPR
• 1 TPR 3 TPR
• 3 TPR 3O2 TPR O2

• (Tetrapyrrols)

Intersystem crossing
Type II
9
Superoxide Anion

• 2H2O Irradiations (Radiolysis) H2O.
  H2O eaq
• 3O2 eaq O2

eaq (Hydrared electron). The electrons are
surrounded by water molecules within 10-12
seconds. Strong reduction agent with 2.84 V.
10
Hydroperoxy and Peroxy Radicals
11
Hydroperoxy Radical

• HO H2O2 HOO H2O
• 2H2O H2O. H2O eaq
• H2O H HO
• H O2 HOO H O2

Radiolysis
Homolysis
(Excited water)
12
Alkylperoxy Radical

• R O2 ROO
• ROO RH ROOH R
• ROOH ROO H
• ROOH Fe3 ROO Fe2
  H

Heat or UV
13
Alkylperoxy Radical

• ROOH HOO ROO H2O2

Reduction potential 1300mv
Reduction potential 1000mv
14
Hydroxy and Alkoxy Radicals
15
Hydroxy Radical

• 2H2O H2O. H2O eaq
• H2O H HO
• H2O. H2O H3O HO

Radiolysis
Homolysis
(Excited water)
H2O
H
16
Hydroxy Radical
UV homolytic fission

• H2O2 2HO
• Fe2 H2O2 Fe3 OH HO

Fenton mechanism
O2 Fe3 O2
Fe2
The reductive half cycle iron catalyst (Fe 3 to
Fe 2) is a rate determining step in Fenton
reaction
17
Hydroxy Radical
Haber-Weiss reaction
H2O2 O2 1O2 OH HO
18
Hydroxy Radical

• ROOH RO OH
• ROOH Fe2 RO Fe3 OH

Heat, UV
Fenton Mechanism
19
Hydrogen Peroxide
20
Hydrogen Peroxide

• O2 O2 H2O2 1O2

Dismutation
21
Hydrogen Peroxide

• HP(Hematoporphyrin) O2 HP O2
• O2 H HOO
• HOO HOO H2O2 1O2

Light and Type II
22
Hydrogen Peroxide
Radiolysis

• 2H2O H2O. H2O eaq
• H2O H HO
• HO HO H2O2

Homolysis
(Excited water)
23
Hydrogen Peroxide

• ROOH HOO ROO H2O2

24
Singlet Oxygen
25
Singlet Oxygen

• H2O2 O2 HO OH 1O2
  

Haber Weiss reaction
26
Singlet Oxygen

• 2R-CHOO-R R-CHOH-R R-CO-R
  1O2

Russell mechanism
27
Reaction Mechanisms of Reactive Oxygen Species
with Food Components
28
Lipids
29
Lipids

• ROO RH ROOH R
• R O2 ROO

30
Lipids

• RH HO R H2O
• R O2 ROO

31
Carotene

• Car OH Car H2O
• Car RO O Car O O R

32
Proteins and Amino Acids
33
Cysteine

• CysSH OH
  CysS H2O
• CysS CysSH
  CysS-SCys H
• CysS O2
  CysSOO
• CysSOO O2 CysSOOOO
• CysSO3O CysSO3OH
  CysSO2OH H2O

Reduction
Reduction
34
Cystine

• CysSSCys OH CysSOH
  CysS
• CysSSCys OH CysSSOH
  Cys
• CysSSOH CysSH CysSSSCys H2O

35
Tocopherol

• T ROO T ROOH
• T ROO TOOR

36
Tocopherol and Ascorbic Acid

• R O2 ROO
• T Asc T
  Dehydroascorbic acid

37
Standard Reduction Potential of Reactive Oxygen
Species
38
Reaction Rates between Reactive Oxygen Species
and Food Components
39
Lipid Reaction Rates (M-1sec-1 )
40
Amino Acids Reaction Rates (M-1sec-1 )
41
Sugars Reaction Rates (M-1sec-1 )
42
Vitamins Reaction Rates (M-1sec-1 )
43
Electronic Configuration of Triplet Oxygen
Molecular
?
Atomic
Atomic
?
?
?
?
2Px 2Py 2Pz
2Pz 2Py 2Px
?
Energy
?
2S
2S
?
44
Electronic Configuration of 2p Antibonding
Orbital of Superoxide Anion
45
Peroxy Radical Formation from the Reaction
between Oleic Acid and Triplet Oxygen
O
(
C
H
)
C
O
H
(
C
H
)
C
H
C
H
C
H
C
H
C
H
2
6
2
2
6
3
2
H
O
O
(
C
H
)
C
O
H
(
C
H
)
C
H
C
H
C
H
C
H
C
H
2
2
3
2
(
C
H
)
C
O
H
(
C
H
)
C
H
C
H
C
H
C
H
C
H
6
6
2
2
3
2
6
6


O


O
2
2
O
O
(
C
H
)
C
H
C
H
C
O
H
(
C
H
)
C
H
C
H
C
H
(
C
H
)
C
O
H
C
H
C
H
(
C
H
)
C
H
C
H
C
H
2
3
2
2
2
2
3
2
6
6
6
6
O
O
O
O
46
Electronic Configuration of 2p Antibonding
Orbital of Singlet Oxygen
47
Excitation and Deactivation of Sensitizer

E
x
c
i
t
e
d

s
t
a
t
e
1
S
e
n
x
-
8
sec
/
10
2
1
k

ISC

S
e
n
3
x

8
h
v
sec
/
10
2
k
x


3
O
2
-

4
sec
/
10
10
k
x
9

sec
/
10
3
k
1
O
1
S
e
n
G
r
o
u
n
d


s
t
a
t
e
2
48
Reaction of Triplet Sensitizer with Substrates
.
3

S
e
n
T
y
p
e
II
T
y
p
e

I


3

O


R
H
2


3

O
2
.
.
.
.

-
R



S
e
n

H
(

o
r


R



S
e
n

)


1
O
2


R
H


3

O
2
.
.
-


S
e
n
O
R
O
O
H
R
O
O
H
2
49
Quenching of Singlet Oxygen
O
2
1



R
H



Q



Q

O


Q



h
e
a
t

----


Q

O


3
2
1

1
2-
Charge transfer
----


Q

O


1
2-

3



Q


O
3
2
50
Production of 1O2 by Photochemical, Chemical,
and Biological Systems
(12)
(1)
ENZYMES
(11)
3
.

SENSITIZER
O
.R
2
R
C
O
O
R
C
O
O

R
RC
O
R
(10)

SENSITIZER
(2)
R
C
R
-
O
H
O
l
ENDOPEROXIDES
C

2
O
2
H
PRODUCTS
-
H
O
C
l

2
(9)
PRODUCTS
(3)
.
O
1
OZONIDES
-
O
O
H

2
2
2
2
_
.
O

O
H
H
.

O
H
H
O
2
(4)
H
O
2
2
.
.
-
(8)
O
H
-
O
H
O

.
2
-
O

H
H
O
e
2
2
2
Y

2H
.
.
.
-
O
-
-
O
O
2

2
2
.
(5)
-
(7)

O

Y
2
(6)
51
Interrelationships among Reactive Oxygen Species
.
2
R
O
O
Carbonyls
.
H
O
O
O


3
Sensitizer
3

2
1
Sensitizer
1
O
2
.
2

-
H
O
F
e
O
H

H2O2
3

F
e
.
.
-
O

Sensitizer
2

H
e
-
H2O2
3
O



O


3
Sensitizer
3

a
q
2

2

R


Enzyme

1
-
3
O
O
H
O
H
O
O
2
2

H
O
2
Fe3 OH_
.
.
.
Irradiation
H2O2 Fe2
H2O2
H2O2
H
O
H
O
R
O
O


H
Irradiation
H
O
2
52
Reactive Oxygen Species Formation from Normal
Metabolism
e-
e-
e-
e-
.-
H2O
O2
O2
H2O2
HO.
H
H
The 1- 5 of consumed oxygen is converted to
reactive oxygen during normal metabolism.
53
Linoleic Acid and Hydroperoxy Radical Reaction
for the Alkyl Radical Formation
.
H
O
O
C
O
O
H

CH3 (CH2)3
C
H
C
H
H
C
C
H
CH
(
C
H
)
7
2
O
O
H
H
O
2
2
C
H
CH3 (CH2)3
)
C
O
O
H
H
C
C
H
C
H
(
C
H
C
H
7
2
O
O.
54
Addition Reaction of Electrophilic Hydroxy
Radical to Oleic Acid
H
C
C
H
C
H
C
(
H
)
(
C
H
)
C
O
O
H
3
2
7
2
7
.


H
O
.
.
C
H
C
H
H
C
C
H
H
C
(
C
H
)
C
O
O
H
H
C
(
C
H
)
(
C
H
)
C
O
O
H
(
C
H
)

2
2
3
7
3
2
7
2
7
7
O
H
O
H
3


O
2
.
.
O
O
O
O
H
C
C
H
H
C
C
H
H
C
(
C
H
)
(
C
H
)
C
O
O
H
H
C
(
C
H
)
(
C
H
)
C
O
O
H

3
2
7
2
7
3
2
7
2
7
O
H
O
H
55
Hydroxy Radical-initiated Oxidation of Linoleic
Acid
.

H
O
H
C
C
H
C
H
C
H
C
H
H
C
(
C
H
)
(
C
H
)
C
O
O
H

3
2
4
2
7
2
HOH
H
C
(
C
H
)
(
C
H
)
C
O
O
H
H
C
C
H
C
H
C
H
C
H
.
3
2
4
2
7
HOH
H
C
(
C
H
)
(
C
H
)
C
O
O
H
H
C
C
H
C
H
C
H
C
H
3
2
4
2
7
-----------------------------------------------
H
C
(
C
H
)
(
C
H
)
C
O
O
H
H
C
C
H
C
H
C
H
C
H
.
3
2
4
2
7
56
Hydroperoxide Formation from Linoleic acid by Ene
Reaction of Singlet Oxygen
O
O
H
1
O
2
O
H
O
Conjugated
O
O
H
1
O
2
O
H
O
Nonconjugated
57
Decomposition of Lipid Hydroperoxides
1
R
2
R
O
H
2
2
1
C
H
C
H
C
H
R
R
O
O
H
O
H
A
B
C
H
C
H
C
H
2
1
R
R
O
B
A

C
H
C
H
2
1
O
H
C
R
R

C
H
C
H
C
H
O
2
1
R
R
3
R
H

O
H

O
H
3
R
H

3
R
3
R
2
C
H
C
H
O
H
R
1
O
H
1
R
R
H
C
H
C
H
2
R
2
C
H
C
H
O
2
R
2
58
Formation of Dioxetane by Singlet Oxygen
1
H
C
N
H
C
C
H
N
H
C

C
H
H
C
N
O

2
O
O
O
O
59
Oxidation of Proteins by Hydroxy Radical
R
R
O
O
1
2
P
C
H
C
N
H
C
C
P
1
2
H
.
H
O
O
R
O
R
1
2
R
O
O
R
4
3
C
H
N
H
C
C
P
.
P
C
1
2

C
.
P
C
H
N
H
C
P
C
3
4
R
O
R
O
1
2


O
P
C
H
C
N
H
C
C
P
2
2
1
R
O
R
O
2
1
P
C
H
C
N
H
C
C
P
P
C
H
C
N
H
C
C
P
3
4
1
2
.
O
O
R
O
R
3
O
4
.


H
60
Oxidation of Proteins by Hydroxy Radical
R
O
R
O
2
1
P
C
H
C
N
H
C
C
P
1
2
O
O
H
R
R
O
.
2
1
O
H
P
N
H
C
O
CH
P
O
C
H
C

2
1
Diamide
R
O
R
O
1
.H
2


P
C
H
C
N
H
C
C
P
1
2
.H


.
O
Amidation
R
O
R
O
1
2
P
N
H

C
H
C
C
C
P
1
2
2
O
.H


R
O
O
R
2
1
P
C
H
C
N
H
C
C
P
1
2
O
H
61
Oxidation of Histidine by Singlet Oxygen
C
O
O
H
C
O
O
H
C
H
H
N
2
C
H
H
N
2
C
H
2
C
H
2
N
C
H
C
O
O
H
H
O
O
C
C
H
N
O
2
Decomposition
1
O

2
N
H
2
O
N
N
H
H
Histidine
Dioxetane
Aspartic Acid
62
Oxidation of Tyrosine by Hydrogen Peroxide
.
H
O
O
2
2



2

H
O

H
O
2
2
2
C
H
C
H
2
2
H
N
C
H
H
N
C
O
O
H
C
H
C
O
O
H
2
2
O
O
O
.
.
.
C
H
C
H
C
H
2
2
2
C
O
O
H
C
H
H
N
C
H
H
N
C
O
O
H
C
H
H
N
C
O
O
H
2
2
2
C
H
N
H
H
O
O
.
2
C
H
2
O
H
O
2
C
H
O
H
2
C
H
H
N
C
O
O
H
C
H
2
Bityrosine
2
C
H
H
N
C
O
O
H
2
63
Formation of Tyrosine Peroxide from Tyrosine
Radical by Superoxide Anion
O
O
O
H



H


H
O
O
-
O
o
r
2



(HOO.)
C
H
C
H
C
H
2
H
O
O
2
2
H
N
C
O
O
H
C
H
H
N
C
O
O
H
C
O
O
H
C
H
C
H
H
N
2
2
2
64
Hydrogen Sulfide from Singlet Oxygen Oxidation of
Cystein
O
O
H
O
O
C
C
H
C
H
S
H

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


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

N
H
2
2

H
S

4

(

S
H
)
S
2

H
S

2
2
2
2
65
Oxidation of Sugars by Hydroxy Radical
R
R
1
1
.
O
H
R
C
H
H
O
H
O
C
O
H

R

.
2
2
2
S
u
g
a
r


O
2
R
R
1
2
.
-
C
O

C
O
H
R





H





O
R
1

2
2
.
O
O


66
Oxidation of ?-carotene by Peroxy Radical
R
O
O
H
.
.


O
C
a
r
C
a
r













R
O
O
2


C
a
r
.

.
C
a
r
O
O
C
a
r
C
a
r
O
O
.
o
r
C
a
r
Carotene epoxide
O
67
Addition Reaction of Peroxy Radical to ?-carotene
.



R
O
O
O
O
R
.
.
.
O
O
R
O.



R
'
O

R
O
O
O
R
O
O
O
'
R
R
O
R
'
O
O

O
68
Hydroperoxide of Ascorbic Acid by Singlet Oxygen
Oxidation
O
H
O
H
O
H
O
O
H
O
O
H
O
O
O
O
H
O
1









O
2
O
O
O
O
H
H
O
O
O
H
H
O
O
H
H
O
69
Oxidation of Ascorbate by Hydroxy Radical
O
H
O
H
O
H
O
O
H
O
O
O
O
H
O
H
O
O
.
.
-
H
O



O
H
-

O
O
O
O
O
H
O
2
Dehydroascorbic acid
Ascorbate
70
Singlet Oxygen Oxidation of Vitamin D
C
H
3
C
H
C
H
3
3
H
C
C
H
3
H
C
H
C
3
C
H
3
C
H
3
3
3
C
H
C
H
3
C
H
C
H
3
C
H
3
C
H
3
3
3
.
1













O
2
O
.
O
O
C
H
2
O
C
H
C
H
2
2
H
O
H
O
H
O
.



2
H
5
,
6
-
e
p
o
x
i
d
e
v
i
t
a
m
i
n

D
C
H
3
H
C
C
H
3
3
C
H
C
H
3
3
O
H
C
H
3
O
H
H
O
O
H
C
H
2
H
O
5
,
6
-
d
i
o
l
71
Reaction of Tocopherol with Peroxy Radical
C
H
3
H
O
.
C
H
3

O
R
O
C
H
3
H
C
O
3
C
H
)
H
(
C
H
C
H
C
H
C
H
2
3
2
2
2
C
H
3
C
H
3
.
O
C
H
3

C
H
R
O
O
H
3
O
H
C
3
C
H
)
H
C
H
C
H
C
H
(
C
H
2
3
2
2
2
C
H
3
.
.



T



R
O
O
C
H
3
Tocopherol Dimer
O
C
H
2
C
H
3
O
H
C



R
O
O
H
C
H
(
C
H
C
H
)
H
C
H
C
H
2
3
2
2
2
3
C
H
3
Semiquinone
72
Singlet Oxygen Oxidation of Tocopherol
C
H
3
C
H
3
O
H
O
O
H
C
H
C
3
C
H
O
3
C
H
1
6
3
3
O
O
H
1
6
3
3
C
H
C
H
3
H
y
d
r
o
p
e
r
x
y
d
i
e
n
o
n
e
3
T
o
c
o
p
h
e
r
o
l
1
O
2
C
H
3
H
O
O
O
H
C
O
3
C
H
1
6
3
3
C
H
3
T
o
c
o
p
h
e
r
o
l

e
n
d
o
p
e
r
o
x
i
d
e
C
H
3
O
O
H
C
O
3
C
H
1
6
3
3
H
O
C
H
3
T
o
c
o
p
h
e
r
y
l

q
u
i
n
o
n
e
73
Soybean Oil Reversion Rancid Flavor by Singlet
Oxygen
74
2-Pentenylfuran from Linolenic Acid by 1O2
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
(
C
H
)
C
O
O
H
2
2
2
6
3
2
2
1O2
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
O
O
H
(
C
H
)
C
H
C
H
2
2
6
2
3
2
2
O
O
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
75
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
H
C
H
C
C
H
C
H
C
H
C
3
2
2
2
2
O
O
C
H
C
H
H
C
H
C
H
C
C
H
C
H
C
H
C
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
76
Sunlight Flavor in Milk Products
77
Formation of Dimethyl Disulfide from Methionine
by Singlet Oxygen
1
H
O
O
C
C
H
C
H
C
H
S

C
H





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

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

C
H
S
3
C
H
S
S
C
H
3
3