PREFACE

Assalamu’alaikum Wr. Wb

First I would like to thank God for the blessing, because only by the permit I could

finish this paper on time.

In this opportunity, I would like to thank for my parents who have given spiritual and

material support and dr. Suweno, Sp. Bkm as my supervisor.

I made this paper to complete my duty in English III and I hope this paper is useful

for all of us. But as a writer, I know that this paper still not perfect and have many mistakes

so I need critic from people who read my paper.

Wassalamu’alaikum Wr. wb

Jakarta, July 2010

Eki Marliani

030.07.079

CONTENS

CHAPTER I

ABSTRACT

An antioxidant is a molecule capable of inhibiting the oxidation of other molecules.

Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing

agent. Oxidation reactions can produce free radicals . In turn, these radicals can start chain

reactions that damage cells . Antioxidants terminate these chain reactions by removing free

radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized

themselves, so antioxidants are often reducing agents such as thiols , ascorbic acid or

polyphenols .

Although oxidation reactions are crucial for life, they can also be damaging; hence,

plants and animals maintain complex systems of multiple types of antioxidants, such as

glutathione , vitamin C , and vitamin E as well as enzymes such as catalase , superoxide

dismutase and various peroxidases . Low levels of antioxidants, or inhibition of the

antioxidant enzymes, cause oxidative stress and may damage or kill cells. As oxidative stress

might be an important part of many human diseases, the use of antioxidants in pharmacology

is intensively studied, particularly as treatments for stroke and neurodegenerative diseases .

However, it is unknown whether oxidative stress is the cause or the consequence of disease.

Antioxidants are widely used as ingredients in dietary supplements in the hope of

maintaining health and preventing diseases such as cancer and coronary heart disease .

Although initial studies suggested that antioxidant supplements might promote health, later

large clinical trials did not detect any benefit and suggested instead that excess

supplementation may be harmful. In addition to these uses of natural antioxidants in

medicine, these compounds have many industrial uses, such as preservatives in food and

cosmetics and preventing the degradation of rubber and gasoline .

CHAPTER II

INTRODUCTION

CHAPTER III

DISCUSSION

Antioxidants in human body

Antioxidants are substances that function call to protect the body from free radical

attack. Are included in the group of these substances include vitamins, polipenol, carotene

and minerals. By nature, these substances are very big role in humans to prevent disease.

Antioxidants do all that by simply pressing the cell damage caused by free radical oxidation

process. Oxidation is a type of chemical reactions involving the binding of oxygen, hydrogen

release, or release electrons. Oxidation process is a natural event that occurs in nature and can

occur everywhere not least in our bodies.

Free radical

Free radical oxygen molecules is actually derived from the chemical structure change

as a result of environmental activities. Environmental activities that can create free radicals

such as radiation, pollution, smoking and so forth.. Free radicals circulating in the body tries

to steal electrons that exist in other molecules such as DNA and cells. This theft if successful

will damage cells and DNA. Can be imagined if the free radicals so many outstanding will

also many damaged cells. Unfortunately, the damage can cause these cells become unstable

which could potentially cause aging and cancer

Classification of antioxidants based on its source

There are two kinds of antioxsidants based on its source , namely the natural antioxsidants

and synthetic antioxidants

Natural antioxsidants

Antioxidant extraction yield natural ingredients. Natural antioxidants in food can be

derived from :

- The existing antioxidant compounds from one or two food components,

- Antioxidant compounds formed from reactions during processing,

- Antioxidant compounds isolated from natural sources and added to food as a food

additive

Antioxidant compounds isolated from natural sources is derived from plants. Natural

antioxidant in several parts of plants, such as in wood, bark, roots, leaves, fruits, flowers,

seeds and pollen.

Synthetics antioxsidants

Antioxidants obtained from the synthesis of chemical reactions. Some examples of

permitted use of synthetic antioxidants for food use has been frequently used. Namely anisol

butyl hydroxy (BHA), butyl hydroxy toluene (BHT), propyl gallate, tert-butyl hidoksi quinon

(TBHQ) and tocopherols. Antioxidant-these antioxidants are natural antioxidants that have

been produced synthetically for commercial purposes.

Sources of antioxidants

Antioxidants can easily be derived from food. Unfortunately many do not know that

these foods actually contain many antioxidants, so they buy antioxidant supplements that cost

is quite expensive. Some examples of food sources of antioxidants, among others:

Vitamin A:

Carrots, broccoli, green vegetables, spinach, pumpkin, liver, potatoes, eggs, apricots,

mangoes, milk and fish.

Vitamin C:

Pepper / pepper, red pepper, parsley, guava, kiwi, broccoli, bean sprouts, persimmon,

papaya, strawberries, oranges, lemons, cauliflower, garlic, wine, raspberri, kepruk

orange, spinach, tomatoes and pineapple.

Vitamin E:

Asparagus, avocados, olives, spinach, nuts, grain, vegetable oil, cereal.

Carotenes:

Beta carotene, lutein, lycopene, carrots, pumpkins, green vegetables, fruit, red fruit,

tomato, seaweed.

Polipenol:

Berri fruit, tea, beer, wine, olive oil, chocolate, coffee, walnuts, peanuts, fruit skins,

pomegranates and wine.

Classification of antioxidants based on its mechanism of action

Based on its mechanism of action, antioxidants divided into primary antioxidant that

can react with free radicals or convert it into a stable product, and secondary antioxidants or

preventive antioxidants that can reduce the initial rate of chain reaction and antioxidant

tertiary . The mechanism of cellular antioxidants by Ong et al . (1995), among others,

antioxidants that interact directly with oxidants , free radicals, or a single oxygen, preventing

the formation of reactive oxygen species; change rekatif oxygen species to less toxic ; prevent

the ability of reactive oxygen species; and repair the damage that may arise.

Primary Antioxidants

Primary antioxidants act to prevent the formation of new free radicals by cutting a chain

reaction and turn it into a product that is more stable . Examples of primary antioxidants, is

the enzyme superoxide dimustase (SOD), catalase , and glutathione dimustase .

Secondary Antioxidants

Secondary antioxidant compounds capture function and prevent the occurrence of radical

chain reactions. Examples of such secondary antioxidants are vitamin E , vitamin C , and β-

carotene .

Tertiary Antioxidants

Tertiary antioxidant function of cells and tissue repair damage caused by free radicals.

Example of enzymes that repair DNA in the cells nucleus is sulfoxideltetrahydrofuran

methionine reductase.

Classification of antioxidants based on soluble

Antioxidants are classified into two broad divisions, depending on whether they are soluble in

water (hydrophilic) or in lipids (hydrophobic) :

Antioxidant

metabolite

Solubility Concentration in human

serum (μM)

Concentration

in liver tissue

(μmol/kg)

Ascorbic acid

(vitamin C)

Water 50 – 60 260 (human)

Glutathione Water 4 6,400 (human)

Lipoic acid Water 0.1 – 0.7 4 – 5 (rat)

Uric acid Water 200 – 400 1,600 (human )

Carotenes Lipid -β-carotene: 0.5 – 1-retinol (vitamin A): 1 – 3

5 (human, total

carotenoids

Tocopherol

(vitamin E)

Lipid 10 – 40 50 (human)[

Ubiquinol

(coenzyme Q)

Lipid 5 200 (human)

Urid acid

The antioxidant in highest concentration in human blood is uric acid , which provides

about half of the total antioxidant capacity of human serum. Uric acid is an oxypurine

produced from xanthine by the enzyme xanthine oxidase , and is a waste product of purine

metabolism in primates, birds, and reptiles. An overabundance of this chemical in the body

causes gout . The effects of uric acid in conditions such as stroke and heart attacks are still

not well understood, with some studies linking higher levels of uric acid with increased

mortality. This apparent effect might either be due to uric acid being activated as a defense

mechanism against oxidative stress, or uric acid acting as a pro-oxidant and contributing to

the damage caused in these diseases.

Ascorbic acid or Vitamin C

Ascorbic acid or " vitamin C " is a monosaccharide oxidation-reduction ( redox )

catalyst found in both animals and plants. As one of the enzymes needed to make ascorbic

acid has been lost by mutation during primate evolution , humans must obtain it from the

diet; it is therefore a vitamin. Most other animals are able to produce this compound in their

bodies and do not require it in their diets. Ascorbic acid is required for the conversion of the

procollagen to collagen by oxidizing proline residues to hydroxyproline .

In other cells, it is maintained in its reduced form by reaction with glutathione, which

can be catalysed by protein disulfide isomerase and glutaredoxins . Ascorbic acid is redox

catalyst which can reduce, and thereby neutralize, reactive oxygen species such as hydrogen

peroxide. In addition to its direct antioxidant effects, ascorbic acid is also a substrate for the

redox enzyme ascorbate peroxidase , a function that is particularly important in stress

resistance in plants. Ascorbic acid is present at high levels in all parts of plants and can reach

concentrations of 20 millimolar in chloroplasts .

Vitamin E or Tocopherols

Vitamin E is the collective name for a set of eight related tocopherols and tocotrienols ,

which are fat-soluble vitamins with antioxidant properties. Of these, α-tocopherol has been

most studied as it has the highest bioavailability , with the body preferentially absorbing and

metabolising this form.

It has been claimed that the α-tocopherol form is the most important lipid-soluble antioxidant,

and that it protects membranes from oxidation by reacting with lipid radicals produced in the

lipid peroxidation chain reactionThis removes the free radical intermediates and prevents the

propagation reaction from continuing. This reaction produces oxidised α-tocopheroxyl

radicals that can be recycled back to the active reduced form through reduction by other

antioxidants, such as ascorbate, retinol or ubiquinol.

This is in line with findings showing that α-tocopherol, but not water-soluble

antioxidants, efficiently protects glutathione peroxidase 4 ( GPX4 )-deficient cells from cell

death GPx4 is the only known enzyme that efficiently reduces lipid-hydroperoxides within

biological membranes.

Glutathione

Glutathione (GSH) is a tripeptide. It contains an unusual peptide linkage between the

amine group of cysteine and the carboxyl group of the glutamate side chain. Glutathione, an

antioxidant, helps protect cells from reactive oxygen species such as free radicals and

peroxides. Glutathione is nucleophilic at sulfur and attacks poisonous electrophilic conjugate

acceptors. Glutathione has multiple functions:

It is the major endogenous antioxidant produced by the cells, participating directly in

the neutralization of free radicals and reactive oxygen compounds, as well as

maintaining exogenous antioxidants such as vitamins C and E in their reduced (active)

forms.

Through direct conjugation, it detoxifies many xenobiotics (foreign compounds) and

carcinogens, both organic and inorganic.

It is essential for the immune system to exert its full potential

It plays a fundamental role in numerous metabolic and biochemical reactions such as

DNA synthesis and repair, protein synthesis, prostaglandin synthesis, amino acid

transport and enzyme activation. Thus, every system in the body can be affected by

the state of the glutathione system, especially the immune system, the nervous system,

the gastrointestinal system and the lungs.

How to Work Antioxidants

If in a place where the reaction of oxidation reaction produces a byproduct of free radicals

(·OH) without the presence of antioxidants the free radicals will attack other molecules

around it.

The result of this reaction will be able to produce another free radical molecule that is ready

to attack another. Eventually will form a very dangerous chain reaction.

Unlike the case when there are antioxidants.. Free radicals will immediately react with

antioxidant molecules to form a stable and not dangerous. Reactions were stopped until here.

Without the presence of antioxidants

Reactant -> product + · OH

OH + (DNA, proteins, lipids) -> Product + other free radicals

Other free radicals which will start the same reaction with a molecule that no diekitarnya.

With the presence of antioxidant

Reactant -> product + · OH

OH + antioxidant -> Items stable

Antioxidants with free radicals tend to react in advance compared with other

molecules because antioxidants are very easily oxidized or strong reducing agents are

compared with other molecules. So the effectiveness of antioxidants depends on how strong

oxidation power compared with other molecules. The more easily oxidized is the more

effective antioxidant.

PICTURE OF ANTIOXIDANTS WORK

Antioxidants protect in cells. How do antioxidants work in our body?

One of the most frequent types of damage done to our body is caused by molecules

known as free radicals. Free radicals are molecules that lose electrons , so that the molecule

becomes unstable and is always trying to take electrons from other molecules or cells. Our

body constantly exposed to the outside world environmentally, physically and mentally.

Environmental wise such as sun rays (ultra violet rays), air pollution, water pollution,

preservative food or poor nutrition diet choice and medications. Physical wise such as

excessive exercise. Mental wise such as stress due to work, relationship and financial

problems.

All the above factors cause free radicals and our body is continuously being

bombarded by these free radicals. And if perform any activities,our body is burning and

producing toxins by reacting with oxygen (which is oxidation: just like the apple cut in half

and turns brown).

CHAPTER IV

CONCLUSION

Antioxidants are substances that function call to protect the body from free radical

attack. Are included in the group of these substances include vitamins, polipenol, carotene

and minerals. By nature, these substances are very big role in humans to prevent disease.

Antioxidants do all that by simply pressing the cell damage caused by free radical oxidation

process.

The result of oxidation of fats in the food turned out to have a major impact on human

health that consume them. Knowledge of how to prevent this oxidation process is necessary,

which in turn is very beneficial in the maintenance of health of each individual. Knowledge

of various types of antioxidants that exist in nature as well as health benefits for the body of

great help in regulating our diet to get healthy and fit body.

Fruits and vegetables are good sources of antioxidants. Buah-buahan dan sayuran

merupakan sumber antioksidan yang baik. So for now, the best way to ensure adequate

intake of the antioxidant nutrients is through a balanced diet consisting of 5-8 servings of

fruits and vegetables per day.

REFERENCES