Baking & Snack - December 2004 - 55

Oxidation of a Polyunsaturated Fatty Acid
* OOCH

HOOCH

CH O
2

*CH

CH2
CH

CH
Step 1

Step 2

Step 3

but not prevent indefinitely, the development of rancidity.

METABOLIC OXIDATION
Some natural metabolic processes, usually
associated with oxidation of food components, generate free radicals in our bodies.
These can initiate a variety of disease conditions including cancer, some types of arthritis, cataracts and coronary disease, to name
just a few. Adverse environmental conditions can exacerbate the situation, increasing
the amount of natural free radical production. Fortunately, while food is in one sense
the root of the problem, it may also be a part
of the solution by providing compounds that
inhibit free radical proliferation.
Cancer is caused (or potentiated) by mutagens, materials that cause mutations of
cellular DNA. A wide variety of mutagens
are known but oxygen free radicals (for
example, singlet oxygen) are high on the
list of "bad actors." Natural antioxidants
lower the level of oxygen free radicals in
cell fluids, lessening the probability of a
mutation that could lead to cancer. Ascorbic
acid (vitamin C) and trace minerals such as
selenium, copper and manganese apparently function in this way, as do many of the
natural phenols discussed below.
Arthritis is due to inflammation of
the tissues in joints. Multiple causes are
known; free radicals are among them.
Cataracts form when free radicals invade
the lens of the eye. This denatures the clear

H2
C

H C
2

CH3

H
C

C
C H3

proteins
leading bonds and aromatic rings. Thus one might
to deposition and expect they would also show antioxidant
*OH
cloudiness.
properties; this is being borne out by reCH
CH
Today,
choles- search. The most common sources of food
terol deposits on pigments are fruits and vegetables. The anCH
CH
arterial walls are tioxidants can be considered mainly in two
CH
CH
familiar to most groups - carotenoids and flavonoids.
readers. Basically,
Carotenoids. Carrots are the eponyStep 4
cholesterol that is mous source of a class of pigments, the
sequestered in lipoproteins is oxidized, and best known of which is beta-carotene (see
in this form, it adheres to the arterial wall "Structure of Beta-Carotene" below). This
forming plaque. As more (oxidized) cho- intensely orange-yellow pigment contains
lesterol is deposited, the opening narrows a long series of conjugated double bonds.
(hardening of the arteries) leading to coro- When an unpaired electron (free radical)
nary disease. Oxygenated free radicals are is "trapped" by a beta-carotene molecule,
strongly implicated in the initial oxidation it is de-energized by being diffused along
step, and antioxidants slow down (although this chain. Epidemiological studies conthey do not reverse) the disease process.
sistently show that high dietary intake
Many natural food components contain and/or high serum level of beta-carotene
aromatic (phenolic) ring structures and is associated with a reduced risk of carcan have antioxidant activity. The amount diovascular disease and certain types of
of antioxidant in a food is measured with cancer, particularly cancers of the lung and
a method called oxygen radical absorbance stomach. Beta-carotene is also the main
capacity (ORAC). To the sample is added dietary precursor of vitamin A, which is
an indicator (a fluorescing protein) that is closely involved with eyesight and also
quenched by free radicals. A peroxygen with immune functions.
radical generator is started, and the
fluorescence of the solution is moniInterception of a Free Radical by BHA
tored. At some point, protein
OH
fluorescence ceases; the
O
amount of peroxy radiC(CH3 ) 3
cal required to reach this
-CH=CH-CH=CH-CHpoint equals the amount
of antioxidant (free radical
absorber) in the solution.
OCH 3
In principle, antioxidant is
titrated with peroxy radiO
cals, and the loss of protein
OH
fluorescence is the endpoint
C(CH3 ) 3
of the titration.
-CH=CH-CH=CH-CHCH

NATURAL ANTIOXIDANTS

Organic pigments usually
contain multiple double

OCH 3

Structure of Beta-Carotene

C H3
C

*OCH

C H3

C
C
H

C
H

CH 3

H
C

C
C
H

C
H

β−Χαροτενε
58 / BAKING & SNACK / December 2004

H
C

C
CH 3

H
C
C
H

H
C
C
CH 3

CH 3

H C
3
C
C
H

H
C 2
CH 2

C
C
C H3

Baking & Snack - December 2004

Table of Contents for the Digital Edition of Baking & Snack - December 2004