Concept of oxidative stress

Oxidative stress is a phenomenon caused by an imbalance between free radicals and antioxidants in favor of the free radicals, leading to a disruption of redox signaling and control and/or molecular damage.

The body produces free radicals during normal metabolic processes. Free radicals are oxygen-containing molecules with an uneven number of electrons. The uneven number allows them to easily react with other molecules.

Free radicals are produced by a variety of normal biological processes including aerobic metabolism and pathogenic defense mechanisms. They can also be a result of external exposures such as radiation, pollutants, and cigarette smoke. Free radicals are highly reactive and are therefore generally short-lived and often unable to leave the subcellular location where they are generated without first becoming reduced.

Because of their high reactivity, they can abstract electrons from other compounds to attain stability. Thus, the attacked molecule loses its electron and becomes a free radical itself, beginning a chain reaction cascade which finally damages the living cell.

Antioxidants are molecules that can donate an electron to a free radical without making themselves unstable. This causes the free radical to stabilize and become less reactive.

The oxidative stress is developed when there is an excess production of free radicals on one side and a deficiency of enzymatic and non-enzymatic antioxidants on the other side.

Oxidative stress can damage cells, proteins, and DNA, which can contribute to aging. It may also play a role in development of a range of health conditions, including diabetes, cancer, and neurodegenerative diseases such as Alzheimer’s. The protection against oxidative damage and chronic diseases is achieved through a variety of endogenous and exogenous antioxidants.
Concept of oxidative stress

Rich antioxidants blueberries

Antioxidant activity

Any substance at low concentrations compared to that of an oxidizable substrate that significantly delays or prevents oxidation of that substrate is called as antioxidant. Antioxidants are involved in the defense mechanism of the organism against the pathologies associated to the attack of free radicals.

It inhibits the oxidation of other molecules. Oxidation is a chemical reaction that transfers electron or hydrogen from substances to an oxidizing agent.

When occurring in the human body, it is a cause for oxidative stress and thought to exert destructive cellular effects associated with pathophysiology of a number of diseases and health conditions, including inflammation, atherosclerosis and ageing, among others

Antioxidants play vital role in preserving the quality of food and maintaining health of human being.

Classification of antioxidant:
*Primary antioxidant
*Oxygen scavengers
*Secondary antioxidants
*Enzymatic antioxidants
*Chelating agents

Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions, when the chain reactions occur in a cell, it can cause damage or death to the cell.

The excess free radicals circulating in the body oxidize the low-density lipoproteins (LDL), making them potentially lethal; the excess free radicals can also accelerate aging processes and have been linked to other very serious pathologies, such as brain stroke, diabetes mellitus, rheumatoid arthritis, Parkinson’s disease, Alzheimer’s disease and cancer. Antioxidants terminate these chain reactions by removing free radical intermediates and inhibit other oxidative reactions.

The effectiveness of antioxidants varies depending on the food and conditions of processing and storage. Antioxidants may lose their effectiveness during high temperature treatment.

Various antioxidants show substantially varying antioxidative effectiveness in different food systems due to different molecular structure. The antioxidants should not impart any off-flavor and off color. It should be able to get conveniently incorporated to food or food systems and should be stable at pH of the food systems and during food processing.

Fruit juices, beverages and hot drinks contain high amounts of antioxidants, like polyphenols, vitamin C, vitamin E, Maillard reaction products, β-carotene, and lycopene. The consumption of fruit juices, beverages and hot drinks was found to reduce the morbidity and mortality caused by degenerative diseases.

Natural antioxidants are extracted, usually in a mixture of several compounds, from variable sources. The composition of the mixture containing active substance(s) and other compounds, which may be inactive or possessing negligible activities, depend on the plant variety, agro-technology, climatic conditions, degree of ripeness, and many other factors.
Antioxidant activity

Concept of antioxidant in food

Antioxidants are a class of chemical substances naturally found in food which can prevent or reduce the oxidative stress of the physiological system.

These are substances or compounds which play crucial role in the prevention of many diseases or disorders as well as cancer. Antioxidants are also said to slow the aging process.

They protect cells in human body from damage that are caused by highly reactive molecules. These highly reactive molecules are called free radicals. Failure of antioxidants to adequately antagonize the toxicity of free radicals causes oxidative stress which ultimately leads to acute and chronic immune; and non-immune injuries to tissues.

Free radicals form in biological systems through metabolism, but it is also realized that exogenous environmental sources, such as radiation, food, and drugs, contribute significantly to the generation of free radicals in biological systems.

Free radical species are unstable and highly reactive or destructive chemicals (i.e. unstable atoms or molecules). Free radicals have an incomplete electron shell that makes them more chemically reactive than molecules with complete electron shells. Free radical might responsible for the cell damage in the body and contribute to various kinds of health problems, such as heart disease, diabetes, macular degeneration, and cancer.

Antioxidants are an inhibitor of the process of oxidation, even at relatively small concentration and thus have diverse physiological role in the body.

A variety of free radical scavenging antioxidants is found in dietary sources like fruits, vegetables and tea, etc. Antioxidants, natural or synthetic food preservatives, are additives that preserve food from “farm to plate”. Due to their high stability and low volatility, the antioxidants help to maintain the level of nutrients, the texture, color, taste, freshness, functionality, aroma, and appeal to consumers such as the older person, ceteris paribus.
Concept of antioxidant in food

Antioxidants as free radical acceptors

In foods containing lipids, antioxidants delay the onset of oxidation or slow the rate at which to proceeds. Their role is not to enhance or improve the quality of foods, but they do maintain food quality and extend shelf life.

The term antioxidant generally refers to compounds that are used to stop the free radical lipid oxidation process. Antioxidants act primary as hydrogen donors or free radical acceptors. The reaction of an antioxidant (AH2) may be represented as follows:

Thus, the primary role of antioxidants is to break the chain reaction of autoxidation by reacting with hydroperoxy radicals. It delay onset or slow the rate of autoxidation by inhibiting the formation of free radicals or interrupting propagation.

Antioxidants can reduce raw material waste, reduce nutritional losses and widen the range of fats that can be use in specific products.
Antioxidants as free radical acceptors

Antioxidant vitamins

The antioxidant vitamins are E and C, as well as beta carotene, a plant form of vitamin A.  The antioxidant function of these vitamins could at least in part, enhance immunity by maintaining the functional and structural integrity of important immune cells.

Oxidation is a process that naturally occurs in the body and natural consequences of it are the radical particles that have since been dubbed as ‘free radicals’. Acting at the molecular level, these antioxidants inactivate a particle of free radicals, which in humans are most commonly ‘activated’ oxygen molecules.

Free radicals can damage basic genetic material, cell walls and other cell structures and eventually this damage can become irreparable and lead to disease.

Some of the basic food groups that prove to be rich sources of antioxidant vitamin are the following:
*Breads, cereals, pasta and starchy vegetables
*Fruits and vegetables
*Fat-free milk and low-fat dairy products
*Lean meat, fish and poultry

A frequent health recommendation to reduce the risk for development chronic disease is to continue at least five servings of fruits and vegetables. A steady supply of antioxidant vitamin should enhance the body’s natural defense mechanism and improve the quality and length of life.

A large body of epidemiologic evidence now supports the role of antioxidant vitamin including ascorbate, alpha-tocopherol and beat-carotene as protective agents against atherosclerotic cardiovascular disease.

A high intake of antioxidant vitamins seems to be protective many kinds of cancer, including oral, esophageal, and reproductive.
Antioxidant vitamins