Consumption of Microwaved Food induces Oxidative Stress in the Liver and Brain of Sprague-Dawley Rats

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IOSR Journal of Environmental Science, Toxicology and Food Technology (IOSR-JESTFT)
e-ISSN: 2319-2402,p- ISSN: 2319-2399.Volume 8, Issue 7 Ver. I (July. 2014), PP 21-24
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Consumption of Microwaved Food induces Oxidative Stress in
the Liver and Brain of Sprague-Dawley Rats
1F. A Ajayi, 2R. O Afolabi , 3C. N Chukwudozie, 4A.A Osuntoki.
1,2,3Department of Biochemistry, College of Medicine of the University of Lagos, Idi-Araba, P.M. B. 12003,
Lagos, Nigeria.
Abstract:
Introduction: Microwaves violently vibrate the water molecules in food, thus creating internal friction. The
radiation, created by microwaves results in the destruction and deformation of food molecules, plus the
formation of new radiolytic compounds..
Methods: In our present study, the susceptibility of microwave radiations on food fed to rats is studied by
measuring antioxidant enzymes catalase, reduced glutathione and superoxide dismutase as well as measuring
the level of TBARS (Thiobarbituric Acid Reacting Substances).
Results: It was observed from the result that the activities of antioxidant enzymes decreased drastically
(p<0.05) in rats fed the microwaved food as compared to their controls.
Conclusion: Microwave radiation affects the oxidative state of the liver and brain macromolecules. Damage
caused by free radicals is aggravated by a reduction in protective antioxidant enzymes caused by the MW
interactions in biological tissues leads to production of ROS that eventually affect the status of the measured
physiological parameters.
I. Introduction
Quite a number of people now make use of the microwave either for thawing or warming of food or
even for fast cooking. As such, virtually every comfortable home now makes use of it. Advantages of
microwave heating include savings in time and energy and easy to use. These advantages make it one of the
most attractive cooking methods. Mechanism of microwave heating is different from the conventional heating.
It represents the conversion of electromagnetic field energy to thermal energy, which arises in the field by polar
water molecules in food (Sumnu, 2001). Bipolar water molecules are rotated in accordance with changes in the
alternating electromagnetic field, which leads to the intermolecular friction and overcoming intermolecular
forces, thus creating heat and leads to rapid heating of material. Microwave can penetrate to the depth of
material, according to the dielectric parameters, thereby heating the material at the same time, both inside and
on the surface. Free radicals are generated from many reactions in the body and can be created in foods from a
combination of oxygen and light or heat that react with a donor molecule. Therefore, free radicals are not
released, but are created. The main target or donor in foods is polyunsaturated fats because they have double
bonds that accept oxygen and form a radical. Butter and margarine contain small amounts of polyunsaturated
fats. For this reason, free radicals can theoretically occur in them when they are subjected to heat or light in the
presence of oxygen. However, these foods also usually contain antioxidants which will reduce the free radicals.
The risk of harm associated with microwaving butter or margarine from free radicals is, in my opinion,
extremely low. (MacDonald, 2004). The unpleasant flavour of oxidized oils has been attributed to the secondary
products of unsaturated fatty acids (Vieira & Regitano-D’Arce 2001). The primary products of lipid oxidation
are hydroperoxides that are generally referred to as peroxides.).
II. Method of Study
Animal Protocol
Twenty four white Sprague-Dawley rats (both male and female) were purchased from the Animal
House of the College of Medicine, University of Lagos, Idi-Araba, Lagos State with body weight range of 108–
188 g. The animals were divided into four main groups (control groups 1 and 3 and the experimental groups 2
and 4 respectively). The formulated feed for the Control groups were not microwaved though with varying oil
types. Microwaved feed however were fed to experimental groups 2 and 4.Animals in each group received
standard (formulated) rat chow and water for six weeks as shown below: A total of 10kg Rat formulated feed
was fed to the rats (fed with normal rat chow) and their weights were monitored. At the end of the respective
experimental periods of 1, 2, 3 4, 5 and 6 weeks, the rats were sacrificed.

Consumption of Microwaved Food induces Oxidative Stress in the Liver and Brain of.....
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Nutrients
Composition
(g)
Carbohydrate source (Rice)
16.6
Protein source (Fish)
1.6
Fat and Oil source (soyabean oil)
0.8
Others (Vitamins, Minerals, Moisture)
1
• Group 1 – Control group with Animal fat (Not microwaved)
• Group 2 – Experimental group with Animal fat (Microwaved)
• Group 3 – Control group with Soya Oil (Not microwaved)
• Group 4 – Experimental group with Soya Oil (Microwaved)
Sample Collection
After twelve hours of fasting, 10ml of blood samples were collected from the rats by occular puncture
and were sacrificed. The blood required for lipid and antioxidant assays was collected in lithium heparinized
tubes. Blood samples were spun at 900g and plasma was collected and stored in a bio-freezer at -200C until
required for the biochemical assays.
Assay method
The antioxidants enzymatic activities assayed for are reduced glutathione, catalase and superoxide
dismutase. The effect of the microwaved food on the rats was studied by measuring these enzymatic activities in
the study groups in comparism with their respective control groups. The reduced glutathione (GSH) content of
liver tissue as non-protein sulphydryls was estimated according to the method described by Sedlak and Lindsay
(1968). Catalase activity was determined according to (Sinha, et.al.,1972). Superoxide Dismutase activity was
determined according to (Sun and Zigma 1978). Lipid peroxidation marker, malondialdehyde was used to
estimate the extent of peroxidation. This was determined using the method of (Buege and Aust 1978).
Statistical analysis
Numerical data were presented as mean values ± standard deviation. The statistical analysis was carried
out by one way ANOVA. The value of p<0.05 was taken as statistically significant using GraphPad Prism 5.
III. Results
Figures 1 and 4 showed that the control groups (1 and 3) had higher antioxidant enzymatic activities
and malondialdehyde as compared with their respective study groups.
Reduced Gluthathione
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0.0
0.1
0.2
0.3
0.4
*
Reduced Glutathione
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0.0
0.1
0.2
0.3
0.4
***
Figure 1: (a) Liver GSH (b) Brain GSH
Superoxide Dismutase
Activity (U/mg protein)
Group 1
Group 2
Group 3
Group 4
0
1
2
3
4
5
Superoxide Dismutase
Activity (U/mg protein)
Group 1
Group 2
Group 3
Group 4
0
2
4
6
8
10
***
Figure 2: (a) Liver SOD (b) Brain SOD

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Catalase Activity
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0
10
20
30
40
**
Catalase Activity
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0
20
40
60
***
Figure 3: (a) Liver CAT (b) Brain CAT
Malondialdehyde
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0.000
0.005
0.010
0.015
0.020
*
**
Malondialdehyde
(U/mg protein)
Group 1
Group 2
Group 3
Group 4
0.0
0.1
0.2
0.3
0.4
Figure 4: (a) Liver MDA (b) Brain MDA
IV. Discussion
The above results have shown that the activities of antioxidant enzymes reduced significantly at P<0.05
both in the liver and brain of the microwaved-food fed rats in the (one and three respectively). When the level of
antioxidants reduces, usually an increased level of pro-oxidants is observed which subsequently results in
oxidative stress. As such, the ability of antioxidants to combat ravaging free radicals thereby stabilizing the
system becomes defeated (Moustafa, 1998). It was observed also that as reduced glutathione depleted, there was
more susceptibility of the study animals to free radicals-mediated damages. This is due to GSH’s detoxifying
role to free radicals deleterious effects (Hassan et al, 2004) including the damage induced by cellular lipid
peroxidation. This observation is in line with some previous work (Fayun et al, 2007).
It is however needful to state that since antioxidants may be endogenously or exogenously produced,
the ability of their system to produce antioxidants to bring a balance between the ‘pro’ and the ‘anti’ was
overridden in the course of this study. This is due to the fact that the rats did not receive other food chows that
are rich in antioxidants for the period of six weeks thus allowing for such a deleterious result. This may not
likely be the case for humans who may get antioxidants from exogenous sources. This explains the drastic
decline in antioxidant activities in these rats.
The extent of oxidative stress was also observed by measuring the lipid peroxidation marker,
malondialdehyde (MDA). MDA was observed to significantly increase in the study groups 2 and 4 rats fed the
microwave food. This results in cellular damage to organs and tissues allowing free radicals to invade the
system. These results indicate that there is an association between the consumption of microwave food and the
oxidative stress through distressing redox balance leading to physiological disturbances. It is therefore
speculated that the changes induced by microwave irradiation may have cascade effect on the several
biochemical processes. The observed increased level of lipid peroxidation, in this study is an indication to a high
production of free radicals during the microwave exposure. These free radicals are highly oxidative moieties
which directly affect the lipid membrane producing oxidative products such as GSSG and lipid peroxidation that
increase also in many diseases and in tissues poisoned by a variety of toxins (Niedemhofer, 2003). The
consequence of this however, is that the body system loses the ability to fight these radicals thus resulting in
many diseases like artherosclerosis, Parkinson’s disease, stoke e.t.c and in tissues poisoned by a variety of

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toxins (Gutteridge, 1993). Study rats of groups 2 and 4 fed with microwaved food were found to be more
susceptible to lipid peroxidation,
Worthy of note also, is the fact that the mechanism of action of the microwave oven may be a reason
for the resulting complications. The microwave oven emits two types of radiation; the microwaves or high
frequency waves and the 60Hz magnetic field. As such, molecules and cells hit by this hard electromagnetic
radiation are forced to reverse polarity one to one hundred billion times a second. Atoms, molecules or cells of
any organic system are usually not able to withstand such a violent destructive power, hence the microwaves
violently vibrate the water molecules in food, thus creating internal friction, thereby heating the food from the
inside out, while other forms of heat including the sun do not create friction heat in organic substances.
This implies that the radiation created by microwaves results in the destruction and deformation of food
molecules, plus the formation of new radio lytic compounds, which are substances that are formed through the
subjection to radiation. These compounds occur more when food is cooked with microwaves than in food that is
cooked by conventional means.
V. Conclusion
The present study suggests that the microwave radiation affects the oxidative state of the liver and
brain macromolecules. It has further been shown that the free radicals mediated damage is aggravated by a
reduction in protective antioxidant enzymes caused by the MW interactions in biological tissues leads to
production of ROS which cause oxidative reactions that eventually affect the status of the physiological
parameters MDA and the activities of antioxidant enzymes. The possible health impacts of MW exposures
continue to raise curiosities as more research works continue to reveal some proven facts through the use of
experimental animals, human experiences and epidemiological studies.
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