Phytochemicals: Types, Examples, and Health Benefits

Phytochemicals are bioactive compounds produced by plants to protect against harmful pathogens, animals, and pests. They can be derived from various sources such as whole grains, fruits, vegetables, herbs, nuts, etc.

They have medicinal properties such as antioxidant activities, antimicrobial, antiviral, anthelmintic, antispasmodic, and antiallergic activities, and are rich in nutrition. They also help alleviate gene transcription, enhance immunity, enhance gap junction communication, and provide protection against various kinds of cancer.
Because of these reasons, they are widely used in the development of functional foods and nutraceuticals.
There have been more than 1000 phytochemicals discovered to date.
Major phytochemicals include terpenoids, alkaloids, flavonoids, carotenoids, polyphenols, saponins, phytosterols, dietary fibers, and some polysaccharides.

Table of Contents

Types of Phytochemicals

Terpenoids

Terpenoids isoprenoids or terpenes comprise one of the largest and most diverse classes of secondary metabolites, occurring in plants.
Terpene is derived from Turpentine (Balsamum terebinthinae), a pleasantly smelling balsam pine tree species. Over 36,000 individual members of the class have been reported and about 1000 more are added each year.
Terpenoids are extremely variable in structure, exhibiting hundreds of different carbon skeletons with a large linkage of functional groups.
They are built up from isoprene, a hydrocarbon consisting of five carbon atoms attached to eight hydrogen atoms (C₅H₈). The synthesis of C₅ building blocks of terpenoids in plants occurs via the mevalonate pathway.
Terpenes can be classified based on the number of isoprene units: monoterpenes contain two such units; sesquiterpenes, three; diterpenes, fours, and so on.
Turpentine, an agent contains several monoterpenes, vitamin A is a diterpene. Similarly, an important plant pigment, carotenoids is best known as tetraterpenes.
Camphor, artemisinin, and paclitaxel (Taxol) are significant pharmaceutical terpenoids.

Phytosterols

Plant sterols, phytosterols, or steroid glycosides, are biochemicals with similar structure and biological functions as cholesterol.
There have been known to be over 250 different sterols and related compounds in plants.
Plant sterols are common in nuts, seeds, and vegetable oils.
They are derived biosynthetically from squalene and a group of triterpenes via the isoprenoid pathway.
The main function of plant sterols is to control membrane fluidity and permeability with specific functions in signal transduction.
Campesterol, beta-sitosterol, and stigmasterol are some examples of phytosterols.

Alkaloids

Alkaloids are an important class of structurally diversified compounds with nitrogen atoms in the heterocyclic ring, derived from amino acids.
These compounds have low molecular weight and constitute about 20% of the known plant secondary metabolites.
Presently, there have been about 12,000 alkaloids isolated from the plant kingdom.
Alkaloids can be classified into varying categories including indole, tropane, piperidine, purine, imidazole, etc.
They protect plants from predators and regulate their growth.
Most of the alkaloids exist in a solid state such as atropine, while others exist as liquids containing carbon, hydrogen, and nitrogen.
Alkaloids end with the suffix ‘-ine’ and are used broadly in pharmaceuticals.
Some popular alkaloids include the analgesics morphine, the muscle relaxant tubocurarine, the additive simulants, caffeine, nicotine, cocaine, etc.

Saponins

Saponins, termed for their ‘soap-like’ persistent foaming when shaken with water, are steroid or triterpene glycosides widely distributed in plants.
They are non-volatile or surface-active compounds that lyse erythrocytes.
Saponins comprise an aglycone part, known as sapogenin which is a steroid or triterpenoid nuclei by which the saponins are classified.
Steroidal saponins are uncommon and mostly distributed in monocotyledonous plants, whereas, triterpenoid saponins are found extensively in dicotyledonous plants.
Saponins have hemolytic and foaming properties which can be characterized by the structural features of saponins and their amphiphilic nature.
This results from the presence of a hydrophilic sugar moiety and a hydrophobic ‘-genin’ (called sapogenin).
Saponins comprise a wide range of pharmacological activities including expectorant, anti-inflammatory, antifungal, antiparasitic, and others.

Phenolic compounds

Phenolic compounds are a diverse class of secondary metabolites that comprise a phenol moiety or hydroxybenzene.
They display a wide range of biological activities such as antioxidants, antimicrobial, and anti-inflammatory properties.
Phenolic compounds are ubiquitous and are found in fruits such as apple, banana, orange, mango, strawberry, etc.
They are classified into flavonoids, stilbenes, phenolic acids, and lignans.
Simple phenolic compounds consist of a single phenol unit or a certain derivative of it. They have a C6 skeleton with an organic group such as alkyl, alkenyl, hydroxy, amino, etc. functional group attached to phenol, and polyphenols, with more than one phenolic unit.
Salicylic acid, caffeic acids, coumarins, and tannins are a few phenolic compounds.

Flavonoids

Flavonoids are plant secondary metabolites having phenolic structures, widely found in vegetables, fruits, and certain beverages.
They are known to have a wide range of health-promoting effects.
Flavonoids have antioxidative, anti-mutagenic, and anti-carcinogenic properties.
In plants, flavonoids are known to synthesize at specific sites including flowers and fruits, giving them color and aroma and development of seedlings.
They are also responsible for protecting plants against biotic and abiotic stresses and act as a unique UV filter.
Presently around 6000 flavonoids have been discovered which contribute to the colorful pigmentation in fruits, vegetables, and medicinal plants.
Flavonoids are classified into flavones, flavanols, flavanones, isoflavones, neoflavanoids, anthocyanins, and chalcones based on the carbon ring on which the B ring is coupled and the degree of unsaturation and oxidation of the C ring.
Quercetin, kaempferol, and quercitrin are some examples of flavonoids.

Polysaccharides and Dietary Fibers

Polysaccharides are a collection of monomer sugar units joined by glycosidic linkage.
They are responsible for the storage of energy in the form of starch and glycogen, or into cellulose, pectin, beta-glucan, hemicelluloses, lignin, etc. known as dietary fiber.
Dietary fiber cannot be digested by humans but are broken down by the gut microbiome in the large intestine.
Plant-based foods such as beans, barley, corn, oats, etc. are good sources of dietary fiber.
Its regular consumption can lead to the prevention of inflammation, hypertension, cancer, hypertension, cardiovascular diseases, promoting a healthy gut microbiome, etc.

Some of the major phytochemicals, their innate role in plants, and their application are:

Phytochemical	Source	Role in plants	Health benefits
Terpenoids
Menthol	Mint plants	Antibacterial and antifungal activity	Aids digestion, reduces pain and irritation,
B-carotene	Carrot, spinach, papaya, mango	Accessory pigments in photosynthesis provides color to plant organs	Source of provitamin A
Taxol (paclitaxel)	Pacific yew tree (Taxus brevifolia)	Protection through antifungal activity against wood-degrading fungi	Blocks cancer cell growth by halting cell division, resulting in cell death
Phytosterols
Campesterol	Nuts, cereals, legumes, vegetable oils	A key precursor to the biosynthesis of plant hormone brassinosteroids	Lowers cholesterol and helps in the prevention of cancer
Stigmasterol	Soybean, rapeseed, rape seed	Stabilizes cell membranes	Precursor to steroid products such as progesterone
Beta-sitostanol	Peanut oil, rice bran, wheat germ, soybean	Stabilizes cell membranes	Lowers cholesterol and inhibits the promotion of cancerous cells
Alkaloids
Caffeine	Coffee beans, tea leaves, cacao pods, guarana plants	Wards off herbivores and pests	Promotes brain activity
Quinine	Cinchona tree		Effective against Plasmodium falciparum(antimalarial activity)
Morphine	Opium Poppy (Papaver somniferum)	Rapidly induces defense system in poppy plant	Relieves pain by acting on Central Nervous System (CNS)
Saponins
Oleanane	Almond, black bean, common bean	Provides defense against pathogenic microbes and herbivores	Antimicrobial activity and aids in the treatment of chronic diseases
Phenolic compounds
Gallic acid	Grapes, strawberries, tea leaves, oak bark	Inhibits plant pathogens, and insects; Protects against Reactive Oxygen Species (ROS)	Exhibits antimicrobial, antioxidant, anticancer, anti-inflammatory, and anti-viral properties
Cinnamic acid	Spice cinnamon	Increases lignin production and inhibits root growth in certain plants	Adds flavor in foods and drinks, aroma in perfumes and cosmetics; Exhibits antibacterial, antifungal, and anti-inflammatory activities
Flavanols	Tea leaves, grapes, chocolate	Regulates cell growth, attracts pollinators, protects against biotic and abiotic stresses	Prevents inflammation and allergies; Acts against free radicals (antioxidant)
Flavonoids
Quercetin	Onions, grapes, citrus fruits	Roles in seed germination, pollen growth, scavenging ROS, photosynthesis	May prevent cardiovascular diseases, reduces inflammation, has antioxidant activity
Anthocyanins	Grapes, apples, red and purple berries, cabbage	Attracts pollinators, protects against UV radiation, scavenging ROS	Prevents diabetes, obesity, cancer, cardiovascular diseases
Rutin	Buckwheat, Eucalyptus tree, Citrus fruits, Japanese Pagoda tree	Induces defense responses against biotic and abiotic stresses	Helps in blood circulation, strengthens capillaries, lowers cholesterol; and antioxidant activity
Polysaccharides
Amylose	Potato, oats, rice	Stores glucose for energy source	Reduces inflammation, hypertension
Amylopectin	Rice, corn, white potato	Stores glucose for energy source	Improves gut microbiome and intestinal health
Dietary fiber
Lignin	Wheat, cabbage, tomato	Major structural component in plant cell wall	Reduces hot flashes in postmenopausal women,
Cellulose	Wheat, rice, jute, corn	Major structural component in plant cell wall	Improves microbiome diversity, reduces bad cholesterol, improves diabetes sensitivity

Conclusion

In conclusion, phytochemicals, the complex bioactive compounds in plants are known for their roles in physiological processes, and in protection against plant biotic and abiotic stresses. It comprises terpenoids, phytosterols, alkaloids, saponins, flavonoids, polysaccharides, and dietary fibers which have several health benefits from promoting a healthy gut microbiome, reducing pain, to treating chronic diseases, and infections, and even cancer. With the discovery of more phytochemicals, it has immense potential for the further development of health, nutraceuticals, and functional foods.

References

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