1. Introduction
1.1 Definition & Mechanism
Antioxidants are substances that protect cell components from being attacked by
oxygen. The adverse effects of free radicals on normal physiological functions of cells will be
decreased significantly with the presence of antioxidants in the body. Thus, cell damage from
oxidation can be reduced or prevented.
Oxygen will trigger the formation of free radicals in the body and this will cause chain
reactions in cells that damage the cell structure and impair cell functions. Research found that
these oxidative damages are linked to the development of many diseases such as Alzheimer’s
disease, atherosclerosis and kidney diseases.
Free radical damages
Polyunsaturated fatty
acid
DNA & RNA
Proteins
Lipid radicals
Altered DNA & RNA
Altered proteins
Impairing cell functions
and eliciting
inflammatory responses
Cell damage, diseases
and aging
Diagram 1.1: Attack of free radicals in the cell components
Diagram 1.2: Metal ion chelating mechanism by free radicals in the cells
Diagram 1.3: Enzyme-catalyzed reaction of free radicals
2. Classification of antioxidants
Antioxidants can be generally categorized into two broad divisions which are natural
and synthetic antioxidants. Examples of natural antioxidants we will discuss are carotenoid
(-carotene), ascorbic acid (vitamin C) and α-tocopherol (vitamin E) whereas examples for
synthetic antioxidants are butylated hydroxyanisol (BHA) and butylated hydroxytoluene
(BHT).
2.1 Natural antioxidants
2.1.1 Carotenoid (-carotene)
Diagram 2.1: Structure of carotenoid, -carotene
Carotenoids possess an extended system of conjugated double bonds that make them
soluble in lipids and capable of quenching singlet molecular oxygen (1O2) and of free radicals.
Because of this ability, carotenoids are thought to be protective against several diseases.
Epidemiological studies have shown that people with high intake of fruits and vegetables,
which are also rich in carotenoid have a lower incidence of diseases such as cardiovascular
disease, cancer, cataracts and age-related macular degeneration. However, some intervention
trials done in Finland show that there is no benefit in cancer prevention for people who has a
long-term smoking habit (Gropper et al., 2009). They even show that intake of -carotene
with vitamin A will further increase the risk of lung cancer and mortality from cancer and
heart disease in the smokers. Contrarily, others suggest that the chance of getting chronic
diseases and lung cancer will be increased only with the cofactors such as alcohol
consumptions and long history of smoking.
2.1.2 Ascorbic acid (Vitamin C)
Diagram 2.2: Structure of ascorbic acid, vitamin C
Vitamin C is one of the important antioxidant that can protect the water-soluble
substances from oxidizing agents. By being oxidized itself, it will regenerate already-oxidized
substances to their original, active form. Some studies suggest vitamin C may reduce the
oxidation of low density lipoprotein (LDL) and raise the level of high density lipoprotein
(HDL) in the body. Therefore, vitamin C may help in reducing the risk of heart diseases.
However, they may act as pro-oxidants which stimulate the formation of free radicals when
there is a high dose of vitamin C. Until the optimum intake of vitamin C is being determined,
ability of vitamin C to reduce the risk of cancer is remained unclear (Whitney et al., 2011).
2.1.3 α-Tocopherol (Vitamin E)
Diagram 2.3: Structure of α-tocopherol, vitamin E
As an antioxidant, vitamin E is a vital compound involved in the termination of free
radicals before the mechanism of free radicals is started. This is due to the self-conversion
ability of vitamin E into a free radical species and thus, termination mechanism occurs when
these two free radicals react to become a molecule which is not a free radical. So, the chain
reactions will be terminated. Some researches show that vitamin E may help in the prevention
of heart diseases by protecting LDL from oxidation and reducing the inflammation (Groff et
al, 2009). This is because oxidation of LDL may leads to atherosclerosis. Several clinical
studies completed over the past 5 years, however, have not shown any beneficial effects of
vitamin E in decreasing risk of death from heart diseases. Therefore, the role of vitamin E in
reducing the risk of heart disease still remains uncertain.
However, some studies proved that vitamin E exerts an important antioxidant effect in
the lungs, the organ with the highest concentration of oxygen (Kohlmeier, 2009). Vitamin E
also protects the lungs from strong oxidants contributed by the air pollutants and as a result,
the risk of lung cancer and bronchitis is also believed to be decreased (Whitney et al, 2013).
2.1.4 Role of Natural Antioxidants in Food
-carotene is always being used as the colouring chemicals in the food industry. This
is because -carotene gives a bright orange colour for the food, mostly in beverage production.
The pigmentation given by the -carotene also give a great pH and heat stability. Besides, it
also acts as pro-vitamin A which is used for fortification of multivitamin juices and
preparation of health supplement food.
For ascorbic acid, it is used widely in the food not only because of their high nutrient
value but also because of their functional contributions to different product quality. Addition
of ascorbic acid is very common in the manufacture of beverages, especially for those fruit
juices. Ascorbic acid can inhibit the enzymatic browning reaction which occurs naturally in
the raw fruit tissues. Browning reaction will lead to formation of melanin and cause the brown
pigmentation in the manufacture of fruit juices. Thus, by adding ascorbic acids, the nutritional
values can be restored and it also contributes to the products’ appearances.
Ascorbic acid is also widely used in the raw meat industry due to its antioxidant
properties. It can be added into the raw meat during storage to prevent oxidation and colour
fading which cause the meat to become brown in colour. However, for cured meat, ascorbic
acid is added to accelerate the oxidation of the meat tissue. This is because the oxidation
imparts the meats to their characteristic colour.
Lastly, tocopherol is always used as antioxidants for protecting the oxidation-sensitive
fatty products. This ensures the better quality of the oil or fatty products and also prolongs
their shelf life at the same time. In addition, it also can be used for fortification of some food
products such as children’s food, packaged cereals and milk powder. Furthermore, vitamin E
also can be added in the vegetable oil to keep them from being oxidized and turn rancid.
Likewise, it protects vitamin A in foods from being oxidized. This makes vitamin E a useful
food preservative.
2.2 Synthetic Antioxidants
Synthetic antioxidants are derived from phenolic structures. Having a phenolic
configuration inside its molecular structure is also form synthetic antioxidant. (Sanhueza et al,
2000). There are many types of synthetic antioxidant, however the most common as synthetic
antioxidants are tertiary-butyl-4-hydroxyanisole or butylated hydroxyanisol (BHA) and 2,6di-tertiary-butyl-4-methylphenol or butylated hydroxytoluene (BHT).
2.2.1 Benefits and Detriments of Synthetic Antioxidants
Diagram 2.4: Structure of butylated hydroxyanisol (BHA)
Diagram 2.5: Structure of butylated hydroxytoluene (BHT)
BHA and BHT are commonly used in food certainly because of their beneficial effects.
However, they have an optimum dose to consume or it will cause negative effects if
consumption exceeds certain dosage. Both BHA and BHT can be added in food up to 0.02 %.
BHA and BHT have good solubility in oils and fats. This allows them to be absorbed
easily by body and stored in the liver. A small portion of BHA and BHT can reduce risks of
majority types of cancer. Due to their good solubility in oils and fats, they can retard the
oxidation of vitamin A, fats and vegetable oil.
However, they can cause a fatty liver and hypercholesterolemia (presence of high level
of cholesterol in blood) and this slows down the ability of liver to metabolize alcohol. BHA
and BHT have been known to impair blood clotting when consumed in high quantities, and
promote tumour growth. (Renouard, 2013)
2.2.2 Roles of Synthetic Antioxidants in Food
Both BHA and BHT are used in baked food because of their thermal stability. BHA
can also be added in packaging food to provide protection inside the package through
volatilization, while BHT is usually mix with BHA to create greater antioxidant activity. BHA
and BHT can be added to frozen foods, beers, cereals, fried foods, instant noodles and canned
food.
In frozen foods, BHA and BHT are effective antioxidant for natural animal fats and
FDA-approved for inclusion in meat and meat products. Though fresh cut meats are unlikely
to contain neither BHA nor BHT, processed meat products, like sausage or packaged frozen
meat-based meals, like chicken nuggets or pre-cooked chicken wings, contain BHA and BHT
in order to stabilize the natural animal fats and any added fats. Meat products that are prebaked or fried contain higher levels of BHA and BHT due to the additional fat and oil used
during processing. (Wahlig, 2011)
As in beers, both BHA and BHT stabilize yeast as effectively as they stabilize fat.
Alcoholic beverages that use yeast as a fermentation agent use BHA/BHT to slow down the
aging process of the food so that the beverage maintains its intended taste and alcohol content
for an extended period of time. BHA/BHT is approved for inclusion in beer to inhibit the
yeast action of the beverage. (Wahlig, 2011)
3. Conclusion
From the elucidation above, it can be concluded that antioxidant can be divided into
two types which are natural and synthetic antioxidant. They can be found in different kinds of
food. Natural antioxidant plays its role in fruits and vegetables whereas synthetic antioxidants
are applied in frozen foods, meats, and beers. Both types of antioxidant give a huge
contribution in food that humans consume especially in terms of preventing diseases such as
cancer and heart disease. Nevertheless, the consumption of antioxidant in diets must be at an
optimum level. This is because the excess intake of antioxidant particularly synthetic
antioxidant may bring various side effects to human body which can further lead to serious
illness.
The mechanism, benefits, detriments, and both types of antioxidant role in food have
been explained above. Thus, the objective of this essay is achieved.
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