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Polyphenols are natural compounds found in cereals, vegetables, fruits, and beverages. Almost 200-300 mg polyphenols are present in fruits like pear, cherries, berries, and grapes per 100 grams’ fresh weight.  A significant amount of polyphenols is also present in the products made from these fruits. 100 mg of polyphenols are present in a cup of tea or a glass of red wine. Chocolate and dry legume also contain polyphenolic compounds.

Polyphenols are considered as secondary metabolites of plants and play an important role in defense against pathogens and ultraviolet radiations. They have a bitter taste and also has astringent properties. Research shows that consuming polyphonic compounds protect against the development of the neurodegenerative disease, osteoporosis, cancer, and cardiovascular diseases. Other than these, there are many other advantages of consuming polyphenolics for human body and prevention against diseases.

What are polyphenols?

Polyphenols are found naturally in herbs, spices, wine, dark chocolate, fruits, and vegetables. They neutralize harmful free radicals due to their antioxidant action and prevent cell damage, which causes many diseases such as diabetes, heart diseases, and cancer. Polyphenols also act as an anti-inflammatory agent and reduce inflammation which is the primary cause of many chronic diseases.

Types of polyphenols

Polyphenols have more than 8,000 types. The four main categories of polyphenols are

  • Flavonoids: They contain 60% of polyphenols. The common examples are anthocyanins, kaempferol, quercetin, and catechins. These are mostly found in dark chocolates, apples, onions, and red cabbage.
  • Phenolic acids: They contain almost 30% of all polyphenols. Examples include lignans and stilbenes that are present in seeds, vegetables, fruits, and whole grains.
  • Polyphenolic amides: It includes avenanthramides and capsaicinoids which are present in oats and chili respectively.
  • Other polyphenols: This group consists of ellagic acid present in berries, lignans in flax seeds, whole grains, and sesame seeds, and curcumin in turmeric.

The quantity and type of polyphenols in foods depend on the food, including ripeness, origin, and how it was farmed, stored, prepared, and transported. There are various supplements available containing polyphenols. However, polyphenols containing foods are more beneficial than supplements.


High-polyphenol foods


The sources of polyphenols from plant based fruits include

  • Fruits: Oranges, apples, apricots, grapes, black elderberries, peaches, grapefruit juice, blackcurrants, plums, cherries, pomegranate juice, raspberries, cranberries, blackberries, strawberries.
  • Beverages: Tea, red wine, Coffee
  • Vegetables: spinach, globe artichoke heads, shallots, asparagus, potatoes, black and green olives, broccoli, carrots, onions
  • Nuts, seeds, and legumes: Roasted soybeans, white beans, almonds, walnuts, chestnuts, hazelnuts, pecans, flaxseed, black beans.
  • Whole grains: Oat flour, whole grain wheat, rye flour
  • Spices and seasonings: cocoa powder, celery seed, dried sage, capers, saffron, dried oregano, dried rosemary, soy sauce, dried spearmint, dried thyme, cloves, dried peppermint, star anise, dried basil, curry powder, cumin, dried ginger.

raspberries contain polyphenols, which are good for health


Bioavailability of polyphenols

We daily consume a variety of foods containing polyphenols, they are an important part of the human diet. However, they are not most active within the body. The major reason is their poor absorption, low intrinsic activity, higher rate of metabolism, and rapid elimination. The biological activity of metabolites differs in various systems of the body. The small intestine is responsible for the absorption of aglycones. The most common forms of polyphenols are glycosides, polymers, and esters that cannot be absorbed in their native forms. The hydrolysis of these substances is necessary by intestinal enzymes or by colonic microflora before their absorption.

Involvement of microflora affects the efficiency of absorption as flora also degrades the aglycones. The conjugation of polyphenols take place in the small intestine and later in the liver. The elimination of polyphenols occurs through bile and urine. Also, they are secreted via biliary route into the duodenum.

What are secondary plant compounds? 

Wide variety of active ingredients present in plants such as glucosinolates, polyphenols, and carotenoids. They are considered as secondary plant compounds because they are not essential for the body. However, they provide certain health benefits to the metabolism.

Secondary plant compounds are chemical compounds formed by the pant cell through metabolic pathways derived from the primary metabolic pathways.

These secondary plant compounds have certain biological effects that’s why their source, whether herb or fruit used as a medicine in ancient times. They can protect plants from pathogens, act as an antibiotic, antiviral and antifungal. They also have essential UV absorbing properties that prevent the damaging of lead from light. These compounds can be classified according to their chemical structure in different classes. These classes have certain therapeutic benefits. The important classes of secondary plant metabolites are

  • Phenolics
  • Lipids
  • Carbohydrates
  • Alkaloids
  • Saponins
  • Terpenes
  • Carotenoids

Applications of microbial secondary metabolites

  • They act as an antibiotic
  • They have antitumor activity
  • Enzymes and enzyme inhibitors
  • Agricultural and animal health products


What is oxidative stress?

Oxidative stress is referred to as the difference between antioxidants and free radicals in the body. Free radicals contain oxygen molecules with an uneven number of electrons. They can react quickly within the body with different molecules and leads to large chain reactions. These reactions are known as oxidation. They can be beneficial or harmful to the body.

Antioxidants can donate an electron to a free radical without making themselves unstable. Due to this, free radical become stable and become less reactive.

There are different factors of oxidative stress and excess production of free radical. These factors are:

  • Diet
  • Environmental factors including pollution and radiation
  • Lifestyle

The other reason for oxidative stress is the body’s natural immune system. This oxidative stress leads to mild inflammation that can be cured after the immune system fights off an infection or repair an injury.

Free radicals are the molecules having one or more unpaired electron. The common examples of free radicals include

  • Reactive oxygen species
  • Hydroxyl radical
  • Superoxide
  • Nitric oxide radical

The excessive production of reactive oxygen species (ROS) in the cells and tissues is also refers ad oxidative stress. Antioxidants cannot neutralize them. This imbalance between antioxidants and (ROS) causes damaging of cellular molecules such as lipids, proteins and DNA.

Reactive oxygen species regulate many cellular functions such as, cell homeostasis, gene expression, signal transduction and activation receptors. Generally, (ROS) are produced in limited quantity in the body. along with the production of reactive oxygen species, nitric oxide is also produced which further causes the production of reactive species such as 4-hydroxynonenal, aldehydes, and malondioaldehyde.

Polyphenols are natural compounds of plants and many biological activities of polyphenols are known. They protect the integrity of the cell by fighting against ROS and RNS and terminate chain reactions. The capacity of polyphenols to act as antioxidant is due to their ability to scavenge a wide range of ROS. The mechanism involved behind the antioxidants capacity is the inhibition of ROS formation by blocking the enzymes essential in their production, scavenging of ROS, or upregulation of protection of antioxidant defenses.

Human diet contains natural antioxidants in the form of polyphenols. The antioxidant activity is related to the free radical scavenger properties and metal ion chelating properties. Polyphenols act as direct free radical scavengers due to their structural features, such as B-ring contain catechol group, etc. In the presence of metal ions and the presence of high doses, polyphenols act ad pro-oxidants leading to DNA degradation.

If the immune system becomes week, it causes oxidative stress and the development of chronic diseases, premature ageing, and acute illness. Common diseases occur due to this are neurodegenerative diseases, diabetes, cardiovascular diseases, and arteriosclerosis.

Effect of polyphenols

Polyphenols strengthen the immune system by fighting against the reactive oxygen species and thus prevent cell structure. They can also interact with vitamins and both reinforce each other.

Bioavailability of polyphenols shows different pattern. The bioavailability of polyphenols become better in the presence of other polyphenols. One of the best and useful polyphenols are flavonoids. They act as antithrombotic, anti-inflammatory, antioxidants, immunomodulatory, and antibiotic. They are shows positive impact on cognitive abilities. Risk of cancer and cardiovascular diseases can also be reduced by flavonoids.


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