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Anti-Oxidants - The Definitive Guide

The Definitive Guide to Anti-Oxidants (All You Need to Know!)

Anti-oxidants are touted to be a core benefit for many health foods, beverages and beauty products. You've probably heard of anti-oxidants, if you have been digging deeper into wellness, nutrition, or even beauty. But what are anti-oxidants, really? In this definitive guide, we simplify the basic concepts involved, as well as the scientific research out there so that you can easily understand everything about anti-oxidants. We walk you through the various forms of anti-oxidants that exist in the world, and in tea in particular. 


1. The Concept of Free Radicals and Oxidative Stress

To start with, it is important to understand the core concept of oxidative stress. And to understand the concept of oxidative stress, it is important to first understand the concept of free radicals. 

Technically speaking, free radicals refers to unstable atoms or compounds present or circulating in the body. For those who remember their chemistry lessons in school, unstable atoms are unstable typically due to the presence of an extra electron, which in turn is likely to combine with another electron from somewhere else to form another free radical. They can either donate an electron to or accept an electron from other molecules, therefore behaving as oxidants or reductants. 

This can trigger a chain reaction and generate a high degree of free radicals in the body, which can then cause damage to the DNA, proteins, fats, carbohydrates, and other molecules in our body. In fact, the likelihood and extent of damage to healthy cells in our body increases with increasing presence of free radicals circulating in the body.

The concept of free radicals is closely related to the concept of toxins in our body. Toxic chemicals, or any other forms of toxins that enter our body, are in fact toxic because of their ability to form free radicals in our body. Toxins of course refers to a broader set of compounds or products that our body is not able to digest or dispose off properly. As a result, toxins start to accumulate in our body, and start triggering off various diseases, blockages of circulatory channels, etc. 

Free radicals and other reactive oxygen species (ROS) are derived either from the usual essential metabolic processes of the human body or from external sources such as exposure to X-rays, ozone, cigarette smoking, air pollutants, and chemicals.

A balance between free radicals and antioxidants in your body is therefore critical for its proper functioning. When there is an overabundance of free radicals, it’s called “oxidative stress.” In other words, in case of excess production, free radicals restrict the body's ability to control them, and the body's cells begin suffering from oxidative stress.

Increased free radicals (or reactive oxygen species (ROS)) may play an important role in the onset of numerous chronic diseases, including cardiovascular diseases, diabetes, Parkinson’s and Alzheimer’s disease, liver and immune dysfunction. In fact, free radicals also contribute to the normal ageing process. As we grow older, our body's ability to fight these free radicals decreases. 

So how do you counteract an increase in toxic free radicals in your body? Consumption of anti-oxidants from external sources can assist the body in coping with this oxidative stress. A healthy lifestyle and intake of generous amounts of antioxidant-rich fruits and vegetables are strongly recommended to combat oxidative stress.

So let us now delve further into the concept of anti-oxidants.


2. Anti-Oxidants

Antioxidants refers to compounds or molecules that help neutralize the effects of free radicals or ROS in the body. An antioxidant essentially is a molecule stable enough to donate an electron to a rampaging free radical and neutralize it, thus reducing its capacity to damage. Anti-oxidants come in various shapes and forms as well.

Technically speaking, they can be of two types: enzymatic and non-enzymatic. Non-enzymatic sources of antioxidants include vitamin C, vitamin E, selenium, zinc, beta carotene and carotene. Examples of enzymatic antioxidants, on the other hand, include catalase, glutaredoxin, and glutathione reductase.

However, as the body ages or matures, its internally generated anti-oxidant levels decline, resulting in an imbalance between anti-oxidants and pro-oxidant molecules. This results in oxidative stress, which perpetuates this vicious cycle by in turn, further reducing the scavenging capacity of antioxidants. Therefore, supplementation with anti-oxidants in your diet or through other mechanisms may help to alleviate oxidative stress. 

Polyphenols Decoded

Anti-Oxidant Activity of Different Beverages

The anti-oxidant activity of different beverages (or even food items for that matter) depends on its bio-chemical composition.

Total antioxidant capacity (TAC) is increasingly considered an important parameter to evaluate the health benefits of beverages. Calculation of the TAC requires a chromatographic analysis of the antioxidant composition of beverages. For the TAC analysis of plant-origin foods and beverages such as fruit juices, tea and wine, chromatographic (and specifically, high-performance liquid chromatographic, HPLC) analysis is utilized. 

Plant-Origin Anti-Oxidants Are Increasing Attracting Attention

In the last decade or so, the search for natural sources of antioxidants that might avoid certain diseases has attracted the attention of researchers. Researchers believe that such diseases may be prevented by a proper and sufficient intake of antioxidants. The research has particularly focused on plant-origin foods and beverages as plant extracts have been shown to have a number of secondary metabolites with antioxidant activity. No wonder then that the scientific community is showing an increased interest in identifying such compounds from plants, as they are likely to have low or no side effects when used to prevent diseases. 

A Diverse Range of Anti-Oxidants Required to Counter Diverse Oxidants

At the same time, it is important to remember that while the antioxidants are beneficial, no one type of antioxidant alone can cope with the negative effects on biological molecules caused by a diverse set of oxidants. It has been demonstrated that multiple types and forms of antioxidants with different properties or benefits are necessary to effectively counter the multiple biological oxidants


3. The Diversity of Anti-Oxidants

Below we offer a brief overview of the different types of anti-oxidants present in plants, such as tea. 


Phytochemicals are essentially compounds that are produced by plants. Such plant-based chemicals are able to provide positive health benefits directly, either by specifically affecting certain genes, or indirectly by impacting metabolic pathways in the body. They are non-essential nutrients, meaning that the body doesn't require them to sustain itself.

Phytochemicals and Polyphenols Family Tree

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Scientists have discovered or know about at least 3,000 different phytochemicals. Commonly found in the human diet, the different types of phytochemicals include, for example, flavonoids, saponins, glucosinolates and capsinoids. For example, some of the most beneficial types of phytochemicals believed to be commonly consumed in the human diet are:

  • beta carotene and other carotenoids in fruits and vegetables (such as carrots, squash, apricots and yam)
  • flavonoids in grains, vegetables and fruits (such as soybeans, chickpeas and licorice)
  • resveratrol in red wine
  • polyphenols in tea
  • antocyanins, found in grapes, blueberries, cranberries and raspberries 
  • isothiocyanates in cruciferous vegetables (members of the cabbage family such as bok choy, broccoli, brussels sprouts, kale, mustard greens, and cauliflower)

It is critical to keep in mind that there is no evidence to suggest that consumption of phytochemical supplements would be as good for you as eating the whole fruits, vegetables, beans, and grains that contain them. Most experts strongly suggest that in order to keep your body healthy, one must consume the combination of these compounds as they exist in natural foods, as opposed to consumption of that isolated phytochemical alone.


Let us now turn our attention to polyphenols, since that is the main type of phytochemicals found in the tea plant. 

Polyphenols, or polyphenolic compounds, are bio-active substances present in various food sources including fruits, vegetables, nuts, cereals, and beverages. Phenols are strong antioxidants and radical scavengers, and can therefore help in maintaining a balance between oxidative stress and antioxidant defense. They have potential health benefits in human anti-oxidation, anti-cardiovascular disease, anti-cancer, anti-diabetes, and anti-neurodegenerative disease. 

As the table above shows, plants are rich in three main classes of polyphenols with beneficial properties: (1) phenolic acids, (2) flavonoids, and (3) other phenolics. Dependent on their chemical structure, polyphenols produce different colors from yellow-green to blue-red. All of these are abundant in fruits, vegetables, spices, and herbs and have both anti-oxidant and anti-inflammatory properties. These can help slow age-related oxidative stress and inflammation, hence assist in minimising some bio-chemical changes that might happen in your body during the process of neuro-degeneration. 

Polyphenols in Fruits and Vegetables

Polyphenols in foods and beverages are related to sensorial qualities such as color, bitterness, astringency, etc., which are relevant in products such as wine, tea and grape juice. These compounds occur naturally in forms varying from simple phenolic acids to complex polymerized tannins.


Flavonoids are a commonly found group of naturally occurring polyphenolic compounds present in fruits, vegetables and plant-derived beverages. Scientists have found more than 8000 compounds with flavonoids structure, and these compounds are often responsible for the unique, distinctive colors of flowers, fruits and leaves.

These compounds provide the plants protection against UV radiation-driven cellular damage, a diverse range of pathogens, and herbivores interested in potentially eating the plant leaves. Being found in abundance in plants, flavonoids are commonly found in the human diet, especially one that is rich in fruits and vegetables.


Catechins are a type of phenolic compound that is very abundant in tea, cocoa and berries. Catechins haven been found to exhibit potent antioxidant activity, especially epigallocatechin-3-gallate (EGCG), which is commonly found in green tea.

Catechins are otherwise present in many products part of a human diet, such as plants, fruits (such as apples, blueberries, gooseberries, grape seeds, kiwi, strawberries), green tea, red wine, beer, chocolate, cocoa, etc. Scientific studies have clearly established the anti-oxidant action of catechins. These studies have notably been validated using various in vitroin vivo and physical methods. 

Catechins Present in Various Plant Sources

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The contents and types of catechins vary greatly among their various sources, and each type possesses varying degrees of anti-oxidant action. High catechin content is typically present in fresh tea leaves, apricots, black grapes, strawberries, and wines. Interestingly, geographic changes also impact the content and variety of catechins in sources such as tea leaves.


Theaflavins, the major polyphenolic components of black tea, include theaflavin 1, theaflavin 2a, theaflavin 2b, and theaflavin 3, and are responsible for the bright red color of black tea. Theaflavins contribute significantly to the characteristic properties of black tea, such as color, mouthfeel, and astringency.

For those so inclined, it is interesting to note the chemistry of the formation of the four major theaflavins in black tea, such as theaflavin, theaflavin 3-gallate, theaflavin 3′-gallate, and theaflavin 3,3′-digallate. These are produced by oxidative coupling between EC and EGC, EC and EGCG, ECG and EGC, and ECG and EGCG, respectively. Theaflavins have unfortunately not been studied as extensively or deeply as catechins, but studies have demonstrated that theaflavins have various anti-oxidant and anti-cancer properties as well. 

Formation of Theaflavins from Catechins


Thearubigins contribute to the brown pigment in black tea, and - much like theaflavins - are also formed by the polymerization of the catechins in tea. Thearubigins account for up to 60% of the water-extractable portion of black tea by dry weight. Again, much like is the case with theaflavins, information and scientific studies about their formation, structures, and contribution to black tea quality is still scarce.


For many centuries now, it has been believed that drinking green tea helps boost relaxation. The compound in tea believed to be responsible for that sense of calm and relaxation, is theanine. Theanine is a unique amino acid found almost solely in tea plants. It is also the main component that is responsible for the characteristic taste of ‘green’ tea.

Studies have demonstrated certain unique properties of L-theanine. L-theanine administered a certain way to rats has been shown to reach the brain directly within 30 minutes, without undergoing any metabolic change. Similarly, studies conducted with human volunteers have shown that oral administration of about 50-200mg of L-theanine caused α-waves to be generated on the occipital and parietal regions of the brain surface within 40 minutes after the oral administration.  Generation of α-waves in the brain signifies relaxation without any accompanying drowsiness.  

The Anti-Oxidant Composition of Tea

As explained above, studying the chemistry of tea shows that the predominant phytochemicals or anti-oxidants present in tea are catechins, theaflavins and thea-rubigins. Studies have found various health benefits of each of these phytochemicals present in tea. 

Polyphenols in Tea

Catechins as we have seen are a type or class of polyphenolic compounds termed ‘flavonoids’. The flavonoids include six major sub-types of compounds: (1) flavones, (2) flavonols, (3) flavanones, (4) anthocyanidins, (5) isoflavones, and (6) flavanols. Catechins belong to the flavanol sub-type, and are specifically categorized as flavan-3-ols.

The major catechins of the tea leaf are epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). These four catechins comprise approximately 25% of the weight of a dry tea leaf. 

Flavonols (kaempferol, quercetin, and myricitin glycosides) are minor flavonoid components of the tea leaf (approximately 3% of dry weight). Polysaccharides and cellulose (approximately 20% of dry weight) and protein (approximately 15% of dry weight) are other major components of the tea leaf, and other nutrients and compounds comprise less than 5% of dry weight each.

Green, oolong, and black, which are the predominantly consumed types of tea, all have slightly different mixes of catechins and polyphenols. The minimal processing of green tea results in high catechin content of 30–40% of the green tea solids. The oxidation process used to form black and oolong teas releases polyphenol oxidase that initiates polymerization and oxidation of the catechins to theaflavins and thearubigins.

In contrast to the heterogeneous and unknown chemical structure of thearubigins, theaflavins are chemically well-defined. There are four primary theaflavins in black tea, which represent between 1 and 6% of the dry weight of the solids (theaflavin, theaflavin 3-gallate, theaflavin 3′-gallate, and theaflavin 3,3′-digallate). Thearubigins represent between 10 and 20% of the dry weight of black tea solids. As oolong tea is processed and fermented only partially (and therfore much less than black tea), it has been found to contain a higher concentration of theaflavins and a lower concentration of thearubigins than black tea. Theaflavins and thearubigins are responsible for the red-amber color of oolong and black tea and for its astringency, and therefore the actual mix of these two compounds will determine the taste and astringency of that particular cup of tea.

Anti-Oxidants Black Tea Chemistry of Tea Composition of Tea Kangra Green Tea Oolong Tea Polyphenols

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