What is the Activity of Antioxidants?

January 11, 2026 •

4 min read

According to a study published in Chemical and Molecular Mechanisms of Antioxidants, the human body uses both endogenous and exogenous antioxidants to neutralize reactive oxygen species (ROS) and maintain cellular health. This crucial process, known as antioxidant activity, involves complex mechanisms that protect the body from oxidative stress.

Quick Summary

Antioxidant activity is the process by which compounds neutralize free radicals through several chemical mechanisms, protecting cells from damage and oxidative stress. This involves scavenging radicals and inhibiting pro-oxidant enzymes.

Key Points

Antioxidant Function: Antioxidants are molecules that neutralize unstable free radicals by donating an electron, halting the chain reaction of cellular damage.
Diverse Mechanisms: Antioxidant activity is achieved through multiple pathways, including Hydrogen Atom Transfer (HAT), Single Electron Transfer (SET), metal chelation, and enzyme regulation.
Endogenous Systems: The human body produces its own antioxidant enzymes, like Superoxide Dismutase (SOD) and Catalase (CAT), as a primary defense against oxidative stress.
Exogenous Sources: Dietary antioxidants, such as vitamins C and E, carotenoids, and polyphenols, are obtained from food and support the body's internal defenses.
Health Protection: By preventing oxidative damage, antioxidants are linked to a reduced risk of chronic diseases like heart disease, cancer, and neurodegenerative conditions.
Measurement Methods: Laboratory techniques like the DPPH, ORAC, and FRAP assays are used to measure the antioxidant activity of substances based on different reaction mechanisms.
Whole Foods are Best: Evidence suggests that obtaining antioxidants from a varied diet of whole foods is more effective than relying on isolated supplements.

The Fundamental Role of Antioxidants

Antioxidants are vital molecules that protect the body from a process called oxidative stress. This occurs when there is an imbalance between the production of free radicals and the body's ability to neutralize them. Free radicals are unstable molecules with an unpaired electron, making them highly reactive and prone to damaging cells, DNA, and other biological structures. Antioxidants counteract this damage by donating an electron to these unstable free radicals, effectively neutralizing them and stopping the chain reaction of damage.

Primary Mechanisms of Antioxidant Action

The activity of antioxidants can be divided into several primary mechanisms through which they neutralize free radicals and mitigate oxidative damage. These mechanisms can be broadly categorized into two main groups, depending on how the antioxidant interacts with the free radical.

Hydrogen Atom Transfer (HAT) This mechanism involves the antioxidant donating a hydrogen atom to the free radical, stabilizing it and preventing further damage. The effectiveness of this mechanism depends on the strength of the bond holding the hydrogen atom within the antioxidant molecule.

Single Electron Transfer (SET) In this process, the antioxidant donates a single electron to the free radical, reducing it and neutralizing its harmful effects. The reaction results in a color change in laboratory tests, which is often used to quantify the antioxidant's strength.

Metal Chelation Some antioxidants can bind to metal ions, such as iron or copper, preventing them from participating in reactions that generate free radicals, like the Fenton reaction. By chelating these metals, antioxidants prevent the formation of highly destructive hydroxyl radicals, providing a preventative defense.

Enzyme Regulation Beyond direct interaction with free radicals, antioxidants can also modulate the body's enzymatic systems. This can involve inhibiting enzymes that produce free radicals or upregulating the activity of the body's natural antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (CAT), which help detoxify cells.

The Body's Endogenous Antioxidant Systems

The body is equipped with its own internal, or endogenous, antioxidant defense system. This system comprises a network of enzymes and non-enzymatic compounds that work synergistically to protect against oxidative damage.

Superoxide Dismutase (SOD): One of the most powerful detoxification enzymes, SOD catalyzes the conversion of superoxide radicals ($O_2\cdot^−$) into hydrogen peroxide ($H_2O_2$).
Catalase (CAT): Following the action of SOD, the catalase enzyme rapidly breaks down hydrogen peroxide into harmless water ($H_2O$) and oxygen ($O_2$).
Glutathione Peroxidase (GPx): This enzyme, which depends on selenium, reduces hydrogen peroxide and lipid peroxides into water and alcohols, protecting cells from lipid peroxidation.

Dietary (Exogenous) Antioxidants

While the body produces its own antioxidants, it also relies on external sources, primarily from diet. These exogenous antioxidants support and enhance the body's natural defense mechanisms.

Vitamins: Vitamin C (ascorbic acid) and Vitamin E (tocopherols and tocotrienols) are well-known dietary antioxidants. Vitamin C is water-soluble and protects against peroxyl radicals in the aqueous phase, while Vitamin E is fat-soluble and protects cell membranes from lipid peroxidation.
Polyphenols: These plant-based compounds, found in fruits, vegetables, and beverages like tea and coffee, can act as hydrogen donors and chelate metal ions. Examples include flavonoids, tannins, and phenolic acids.
Carotenoids: These pigments, including beta-carotene, lycopene, and lutein, act as potent radical scavengers, especially in the protection of cell membranes. They are responsible for the red, orange, and yellow colors of many fruits and vegetables.
Trace Minerals: Minerals like selenium and zinc are also essential for antioxidant activity, as they serve as cofactors for antioxidant enzymes.

Comparison of Antioxidant Activity Measurement Methods

Evaluating the activity of antioxidants requires various in vitro (laboratory) methods, which often differ based on their underlying chemical principles.


Assay Method	Mechanism	Principle	Key Advantage	Key Limitation
DPPH Assay	SET or HAT	Measures the scavenging of the stable DPPH radical by monitoring its discoloration.	Simple, fast, and reproducible.	Not specific to physiological conditions; affected by light.
ORAC Assay	HAT	Measures the inhibition of peroxyl radical-induced oxidation using a fluorescent probe.	Reflects physiological hydrogen-donating capacity.	Can be influenced by experimental conditions like temperature.
FRAP Assay	SET	Quantifies the reduction of ferric ($Fe^{3+}$) to ferrous ($Fe^{2+}$) ions by antioxidants.	Excellent for determining reducing power of a sample.	Only measures reducing power, not radical scavenging directly.
ABTS Assay	SET or HAT	Measures the decay of the pre-formed ABTS radical cation in the presence of an antioxidant.	Versatile for both hydrophilic and lipophilic substances.	Less specific than other tests; results can be pH-dependent.
Folin-Ciocalteu Assay	SET	Determines the total phenolic content based on their reductive capacity.	Common and standardized for total phenolic content.	Prone to overestimation due to other reducing agents present.

The Link Between Antioxidant Activity and Health

The activity of antioxidants is crucial for maintaining cellular health and preventing the damage associated with oxidative stress. An overproduction of free radicals can contribute to the development of numerous chronic diseases, including cardiovascular disease, cancer, diabetes, and neurodegenerative conditions like Alzheimer's and Parkinson's. Antioxidants provide a defense system that helps mitigate this damage. For instance, a diet rich in plant-based antioxidants, like polyphenols and carotenoids, has been linked to a reduced risk of various diseases. However, obtaining antioxidants from whole foods is generally considered more beneficial than supplements, as the synergistic effects of compounds within the food provide greater protection.

Conclusion

Understanding what is the activity of antioxidants reveals a complex and essential biological defense system. These compounds act through multiple mechanisms, including donating electrons or hydrogen atoms, chelating metals, and regulating enzymes, to neutralize harmful free radicals. The body maintains its own internal antioxidant systems, supported and enhanced by a diet rich in exogenous antioxidants from fruits, vegetables, and other plant-based foods. While various laboratory methods exist to quantify this activity, the most significant takeaway is the importance of a varied diet to ensure a full spectrum of antioxidant support for maintaining long-term health and preventing oxidative damage.

Frequently Asked Questions

The main purpose of antioxidant activity is to neutralize free radicals, which are unstable molecules that can cause damage to cells and DNA. By neutralizing these radicals, antioxidants protect the body from oxidative stress and help prevent chronic diseases.

No, not all antioxidants are the same. 'Antioxidant' is a functional term describing what a substance does, not a specific chemical. There are many types, each with unique chemical properties and mechanisms of action, such as scavenging radicals, chelating metals, or regulating enzymes.

Common dietary sources of antioxidants include a wide variety of plant-based foods. This includes fruits like berries and citrus, vegetables such as spinach and kale, nuts, seeds, and beverages like coffee and green tea.

Current research and health guidelines suggest that obtaining antioxidants from a diet rich in whole foods is more beneficial than taking supplements. The synergistic effect of the various compounds in food provides greater overall protection.

Oxidative stress is a condition resulting from an imbalance between the production of free radicals and the body's ability to counteract their harmful effects. It can lead to cell damage and has been linked to numerous chronic diseases.

Yes, cooking can affect the antioxidant levels in food. Some antioxidants, like lycopene in tomatoes, become more bioavailable with cooking, while others, like vitamin C, may be reduced or destroyed by heat.

Antioxidant enzymes are produced by the body and act as a first line of defense against free radicals. They convert reactive oxygen species into less harmful substances. For example, Superoxide Dismutase (SOD) converts superoxide into hydrogen peroxide.