Phytochemicals are bioactive compounds naturally produced by plants to defend against harmful pathogens, animals, and pests.
They are obtained from various sources including whole grains, fruits, vegetables, herbs, nuts, and more.
These compounds possess medicinal properties such as antioxidant, antimicrobial, antiviral, anthelmintic, antispasmodic, and antiallergic activities.
Phytochemicals are also rich in nutritional value.
They contribute to the regulation of gene transcription.
They help enhance the immune system.
They improve gap junction communication between cells.
They offer protection against various types of cancer.
Due to these beneficial effects, phytochemicals are commonly utilized in the formulation of functional foods and nutraceuticals.
Over 1000 different phytochemicals have been identified to date.
Major categories of phytochemicals include terpenoids, alkaloids, flavonoids, carotenoids, polyphenols, saponins, phytosterols, dietary fibers, and certain polysaccharides.
Types of Phytochemicals
Terpenoids
Terpenoids, also known as isoprenoids or terpenes, represent one of the largest and most diverse classes of secondary metabolites found in plants.
The term "terpene" originates from Turpentine (Balsamum terebinthinae), a fragrant balsam obtained from pine trees.
More than 36,000 individual terpenoids have been reported, with around 1,000 new ones identified each year.
Terpenoids show great structural diversity, with hundreds of different carbon skeletons and a wide variety of functional groups.
They are synthesized from isoprene, a hydrocarbon with five carbon atoms and eight hydrogen atoms (C₅H₈).
In plants, the C₅ building blocks of terpenoids are produced through the mevalonate pathway.
Terpenes are classified based on the number of isoprene units they contain:
Monoterpenes: 2 isoprene units
Sesquiterpenes: 3 isoprene units
Diterpenes: 4 isoprene units
Tetraterpenes: 8 isoprene units
Turpentine contains several monoterpenes, while vitamin A is an example of a diterpene.
Carotenoids, important plant pigments, are classified as tetraterpenes.
Notable pharmaceutical terpenoids include camphor, artemisinin, and paclitaxel (Taxol).
Phytosterols
Phytosterols, also known as plant sterols or steroid glycosides, are biochemicals that share a similar structure and biological role to cholesterol.
More than 250 different sterols and related compounds have been identified in plants.
Phytosterols are commonly found in nuts, seeds, and vegetable oils.
They are biosynthesized from squalene and a group of triterpenes through the isoprenoid pathway.
The primary function of plant sterols is to regulate membrane fluidity and permeability, playing a role in signal transduction.
Common examples of phytosterols include campesterol, beta-sitosterol, and stigmasterol.
Alkaloids
Alkaloids are a significant class of structurally diverse compounds containing nitrogen atoms within a heterocyclic ring, and are derived from amino acids.
These compounds are of low molecular weight and make up about 20% of all known plant secondary metabolites.
Approximately 12,000 alkaloids have been isolated from plants to date.
Alkaloids are classified into various categories such as indole, tropane, piperidine, purine, and imidazole.
They play a protective role for plants against predators and also help in regulating plant growth.
Most alkaloids exist in solid form, like atropine, while some occur as liquids composed of carbon, hydrogen, and nitrogen.
Alkaloid names typically end with the suffix “-ine” and they are widely used in pharmaceutical formulations.
Well-known alkaloids include morphine (an analgesic), tubocurarine (a muscle relaxant), and stimulants like caffeine, nicotine, and cocaine.
Saponins
Saponins are named for their ‘soap-like’ persistent foaming when mixed with water and are steroid or triterpene glycosides widely distributed in plants.
They are non-volatile, surface-active compounds known to lyse erythrocytes.
Saponins consist of an aglycone portion called sapogenin, which contains either a steroid or triterpenoid nucleus used for classification.
Steroidal saponins are relatively rare and are primarily found in monocotyledonous plants.
Triterpenoid saponins are more common and predominantly found in dicotyledonous plants.
The hemolytic and foaming properties of saponins are due to their amphiphilic structure.
This amphiphilic nature results from the combination of a hydrophilic sugar moiety and a hydrophobic sapogenin ('-genin') part.
Saponins exhibit a broad spectrum of pharmacological activities including expectorant, anti-inflammatory, antifungal, and antiparasitic effects.
Phenolic compounds
Phenolic compounds are a diverse group of secondary metabolites that contain a phenol moiety or hydroxybenzene structure.
They exhibit a wide range of biological activities, including antioxidant, antimicrobial, and anti-inflammatory effects.
These compounds are widespread in nature and commonly found in fruits such as apples, bananas, oranges, mangoes, strawberries, and others.
Phenolic compounds are categorized into flavonoids, stilbenes, phenolic acids, and lignans.
Simple phenolic compounds consist of a single phenol unit or its derivatives, typically with a C6 skeleton attached to functional groups such as alkyl, alkenyl, hydroxy, or amino groups.
Polyphenols contain more than one phenolic unit.
Examples of phenolic compounds include salicylic acid, caffeic acid, coumarins, and tannins.
Flavonoids
Flavonoids are plant secondary metabolites with phenolic structures, commonly found in vegetables, fruits, and certain beverages.
They are recognized for a wide variety of health-promoting benefits.
Flavonoids exhibit antioxidative, anti-mutagenic, and anti-carcinogenic properties.
In plants, they are synthesized at specific sites such as flowers and fruits, contributing to color, aroma, and seedling development.
Flavonoids protect plants from both biotic and abiotic stresses and function as natural UV filters.
Approximately 6000 flavonoids have been identified, playing a key role in the pigmentation of fruits, vegetables, and medicinal plants.
They are categorized into flavones, flavanols, flavanones, isoflavones, neoflavonoids, anthocyanins, and chalcones based on the carbon ring structure and the degree of unsaturation and oxidation of the C ring.
Common examples of flavonoids include quercetin, kaempferol, and quercitrin.
Polysaccharides and Dietary Fibers
Polysaccharides are composed of multiple sugar monomers linked together by glycosidic bonds.
They serve as energy storage molecules in the form of starch and glycogen, or as structural components like cellulose, pectin, beta-glucan, hemicelluloses, and lignin, which are collectively known as dietary fiber.
Dietary fiber is indigestible by humans but can be broken down by gut microbiota in the large intestine.
Plant-based foods such as beans, barley, corn, and oats are rich sources of dietary fiber.
Regular intake of dietary fiber helps prevent inflammation, hypertension, cancer, and cardiovascular diseases, while also promoting a healthy gut microbiome.
Applications of Phytochemicals
Terpenoids
Menthol, found in mint plants, provides antibacterial and antifungal protection. In humans, it aids digestion and relieves pain and irritation.
β-Carotene, present in carrots, spinach, papaya, and mango, serves as an accessory pigment in photosynthesis and adds color to plant organs. It acts as a provitamin A source, crucial for vision and immune function.
Taxol (paclitaxel), derived from the Pacific yew tree, protects the plant from wood-degrading fungi. Medically, it’s a powerful anticancer agent that inhibits cell division in cancer cells.
Phytosterols
Campesterol, found in nuts, cereals, legumes, and vegetable oils, is a biosynthetic precursor of brassinosteroids in plants. It helps lower cholesterol and may reduce cancer risk.
Stigmasterol, from soybeans and rapeseed, stabilizes cell membranes and is a precursor for hormones like progesterone.
Beta-sitostanol, found in peanut oil, rice bran, and wheat germ, contributes to membrane stabilization and helps lower cholesterol while suppressing the development of cancerous cells.
Alkaloids
Caffeine, present in coffee, tea, cacao, and guarana, deters herbivores and pests. In humans, it enhances alertness by stimulating the brain.
Quinine, obtained from the cinchona tree, has strong antimalarial properties, especially against Plasmodium falciparum.
Morphine, derived from the opium poppy, rapidly activates the plant’s defense systems and acts as a potent pain reliever by acting on the central nervous system.
Saponins
Oleanane, found in almonds and beans, protects plants from pathogens and herbivores. It possesses antimicrobial properties and aids in managing chronic diseases.
Phenolic Compounds
Gallic acid, from grapes, strawberries, and tea, protects plants from pathogens and oxidative stress. It has antimicrobial, antioxidant, anticancer, and anti-inflammatory benefits.
Cinnamic acid, found in cinnamon, enhances lignin production and restricts root growth in competing plants. It adds flavor and aroma and has antibacterial and anti-inflammatory activities.
Flavanols, in tea, grapes, and chocolate, support plant growth regulation and stress defense. They help reduce inflammation and allergic reactions in humans and combat free radicals.
Flavonoids
Quercetin, from onions, grapes, and citrus fruits, aids seed germination, pollen development, and scavenges reactive oxygen species (ROS). It may help prevent cardiovascular disease and inflammation.
Anthocyanins, found in grapes, apples, and red or purple berries, attract pollinators and offer UV protection. They help prevent diabetes, cancer, and cardiovascular diseases.
Rutin, present in buckwheat and citrus fruits, supports plant stress responses. It improves circulation, strengthens capillaries, and lowers cholesterol.
Polysaccharides
Amylose, in potatoes, oats, and rice, stores glucose in plants. It reduces inflammation and blood pressure in humans.
Amylopectin, from rice and corn, also stores glucose and enhances gut and intestinal health.
Dietary Fiber
Lignin, present in wheat and cabbage, is a structural plant cell wall component. It helps alleviate menopausal symptoms like hot flashes.
Cellulose, found in wheat, rice, and jute, is a primary structural element in plant cell walls. It supports gut microbiome diversity, lowers cholesterol, and enhances insulin sensitivity.
Conclusion
In conclusion, phytochemicals, the complex bioactive compounds found in plants, play crucial roles in plant physiology and protect plants from biotic and abiotic stresses.
They include terpenoids, phytosterols, alkaloids, saponins, flavonoids, polysaccharides, and dietary fibers, all of which offer a range of health benefits.
These benefits range from promoting a healthy gut microbiome and reducing pain to managing chronic diseases, treating infections, and even fighting cancer.
As the discovery of new phytochemicals continues, their potential for the development of health products, nutraceuticals, and functional foods is vast, offering exciting prospects for the future of human health and wellness.
References
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