The key difference between alkaloid and flavonoid is that alkaloid is an amino acid-derived nitrogen-containing organic compound found in plants, animals, fungi and bacteria while flavonoid is a natural compound found in plants that do not contain nitrogen.
Alkaloids and flavonoids are two groups of natural compounds found mainly in plants. They are organic compounds produced as secondary metabolites. Alkaloid is a cyclic organic compound which contains at least one nitrogen atom. They show basic properties. Flavonoids are natural compounds that contain two benzene rings linked via a heterocyclic pyran ring. Both are considered as two major classes of plant organic compounds. They usually coexist in many medicinal plants.
CONTENTS
1. Overview and Key Difference
2. What is an Alkaloid
3. What is a Flavonoid
4. Similarities Between Alkaloid and Flavonoid
5. Side by Side Comparison – Alkaloid vs Flavonoid in Tabular Form
6. Summary
What is an Alkaloid?
An alkaloid is a naturally occurring nitrogen-containing basic organic compound primarily found in plants. They are heterocyclic compounds. They are also produced by a large variety of organisms including bacteria, fungi and animals. Certain families of flowering plants are known to contain alkaloids. Some of them are rich in alkaloids. For example, opium poppy plant has about 30 different types of alkaloids.
There are several thousands of identified alkaloids. Moreover, there are several classes of alkaloids, including indoles, quinolines, isoquinolines, pyrrolidines, pyridines, pyrrolizidines, tropanes, terpenoids and steroids. Morphine (a powerful narcotic used for the relief of pain), codeine (an excellent analgesic), strychnine (another powerful poison), quinine (a powerful antimalarial agent), ephedrine (used in bronchial asthma and to relieve the discomfort of hay fever, sinusitis, and common colds), quinidine (used in the treatment of irregular rhythms of the heartbeat or arrhythmias) and nicotine (the chief addictive ingredient of the tobacco smoked in cigarettes, cigars, and pipes) are several well-known alkaloids.
Figure 01: Alkaloid
In pure form, alkaloids are colourless and have a bitter taste. Alkaloids exist as an aqueous solution in tissues. They can be isolated using a special method called extraction. High-performance thin-layer chromatography (HPTLC) is another method which can be used to isolate alkaloids.
Many alkaloids are elements of the human diet. Some alkaloids are narcotic drugs, and they are highly addictive. Similar to flavonoids, alkaloids have diverse and important physiological effects on humans and other animals. They show anti-inflammatory, anticancer, analgesics, local anaesthetic and pain relief, neuropharmacological, antimicrobial, antifungal, and many other properties. Furthermore, many alkaloids have important pharmaceutical uses. The exact role of alkaloids in plants is yet unknown. In some plants, the production of alkaloids increases just before the seed formation. In addition to these, alkaloids help to protect some plants from certain insect species.
What is a Flavonoid?
Flavonoid is a naturally occurring polyphenolic compound found in plants. Structurally, a flavonoid has a fifteen-carbon skeleton containing two benzene rings linked via a heterocyclic pyran ring. Plants synthesize flavonoids in response to microbial infection. They are produced via phenylpropanoid pathway. Flavonoids can be classified into several classes such as flavones (e.g., flavone, apigenin, and luteolin), flavonols (e.g., quercetin, kaempferol, myricetin, and fisetin), flavanones (e.g., flavanone, hesperetin, and naringenin), and others.
Figure 02: Flavonoid
Flavonoids exhibit versatile health benefits. They have antioxidative activity, free radical scavenging capacity, coronary heart disease prevention, hepatoprotective, anti-inflammatory, and anticancer activities. Moreover, they show potential antiviral activities. They also help in combating oxidative stress in plants. In addition, they work as growth regulators in plants.
Fruits and vegetables are the main dietary sources of flavonoids for humans. Onions, tea, strawberries, kale, grapes, Brussels sprouts, citrus fruit, parsley, and many spices are few natural foods rich in flavonoids. In fact, almost all fruits, vegetables and herbs contain flavonoids. The vivid and attractive colours in leaves, fruits and vegetables are mainly due to flavonoids. They are often concentrated in the skins and outer areas of fruits and vegetables.
What are the Similarities Between Alkaloid and Flavonoid?
- Alkaloid and flavonoid are naturally occurring organic compounds found mostly in plants.
- They are useful dietary ingredients.
- Both compounds are useful in curing diseases and improving human life.
- They have antioxidative activity, anti-inflammatory and anticancer activities.
- Moreover, they are low molecular weight compounds.
- They are considered as secondary metabolites.
What is the Difference Between Alkaloid and Flavonoid?
Alkaloid is a nitrogen-containing organic compound found in plants, animals, fungi and bacteria. Flavonoid is a polyphenolic secondary metabolite found in fruits, vegetables and plant-derived beverages. So, this is the key difference between alkaloid and flavonoid.
The below infographic summarizes the difference between alkaloid and flavonoid in tabular form.
Summary – Alkaloid vs Flavonoid
Alkaloids and flavonoids are naturally occurring compound mostly found in plants. Both types are excellent antioxidants. They also play key roles in the prevention and curing of diseases. Both types of compounds show a broad spectrum of health-promoting effects. Alkaloids are nitrogen-containing low molecular weight compounds found in plants, animals, fungi and bacteria. Flavonoids are low molecular weight phytochemicals which do not contain nitrogen. Thus, this summarizes the difference between alkaloid and flavonoid.
Reference:
1. Kurek, Joanna. “Introductory Chapter: Alkaloids – Their Importance in Nature and for Human Life.” IntechOpen, IntechOpen, 13 Nov. 2019, Available here.
2. Kumar, Shashank, and Abhay K. Pandey. “Chemistry and Biological Activities of Flavonoids: An Overview.” The Scientific World Journal, Hindawi, 29 Dec. 2013, Available here.
3. Panche, A N, et al. “Flavonoids: an Overview.” Journal of Nutritional Science, Cambridge University Press, 29 Dec. 2016, Available here.
Image Courtesy:
1. “Papaver somniferum 01”(CC BY-SA 2.0) via Commons Wikimedia