Did you eat an apple today, sip tea, or sauté red onions? Or maybe you ate fruits or other vegetables like tomatoes, broccoli, grapes, mangoes, or berries. Did you know that there is a phytochemical compound found in all of the mentioned sources? The compound is a flavonoid called quercetin. Flavonoids are secondary metabolites, and all plants produce them, and quercetin is one of those flavonoid compounds. As mentioned earlier, flavonoids can be found in many fruits and vegetables that are commonly consumed daily. However, it turns out that quercetin has greater potential than just being one of the components in everyday food. Let's discuss this compound further.
Introducing Quercetin
Quercetin (C15H10O7) is included in the flavonol group, one of the six sub-groups of flavonoids, and has the IUPAC nomenclature 3,3′,4′,5,7-Pentahydroxyflavone. Pure quercetin has a solid crystalline yellow form1. Although it can be found in many plants, the name quercetin is derived from the Latin word quercetum, which means Quercus robur or oak plant2.
Quercetin has five hydroxyl groups that play an important role in defining the biological activity of this compound and the number of derivatives that can be obtained from this compound3. The most common derivatives of quercetin are glycosides, or the bond of quercetin with sugar, such as isoquercetin which is quercetin that has a bond with monosaccharide sugar or rutin which is quercetin that has a bond with disaccharide sugar4.
Although it has a hydroxyl group, quercetin has very low solubility in water, while derivatives of quercetin can be either water-soluble or slightly water-soluble depending on the type of molecular substituents. In general, derivatives of O-methyl, C-methyl, and prenyl from quercetin are lipophilic, while quercetin with hydroxyl groups that are glycosylated will become more hydrophilic because each glycosylated hydroxyl group will increase the hydrophilicity of the compound3.
Sources of Quercetin
Quercetin is widely found in food sources such as apples, grapes, onions and scallions, tea, tomatoes, and various vegetables as well as herbal sources such as Ginkgo biloba and Hypericum perforatum5. The sources that have the highest quercetin content are capers, juniper berry, okra, elderberry, corn poppy, coriander, dill, and bee pollen6.
The main group of quercetin derivatives includes glycosides, esters, sulfates, and prenyl, but the group of quercetin derivatives most commonly found in nature is glycosides. Some examples of quercetin derivatives and their sources are as follows.
1. Quercetin 3-O-galactoside, can be found in mango, blueberry, plum, cranberry, and lingonberry
2. Quercetin 3-O-glucoside, can be found in mango, plum, and onion
3. Quercetin 3-O-rhamnoside, can be found in mango, pepper, spinach, olive oil, and cranberry
4. Quercetin 3-O-glucuronide, can be found in lettuce
5. Quercetin 3-methyl ether and Quercetin 3,3’-dimethyl ether, can be found in honey,
6. Quercetin 2,4’-diglucoside, can be found in onion, as well as many other quercetin derivatives3.
Activity and Potential of Quercetin
Based on several in vitro and in vivo, quercetin has biological activity that serves as the basis for the potential of quercetin in various aspects including resilience and overall body health, anti-carcinogenic, antiinflammatory, antiviral, antioxidant, the ability to inhibit lipid peroxidation, platelet aggregation, and capillary permeability, as well as the ability to stimulate mitochondrial biogenesis1.
1. Antioxidant
Quercetin has antioxidant activity with quite high effectiveness which is suspected to be due to the presence of hydroxyl groups on its benzo-dihydropyran ring, giving quercetin a high antioxidant capacity, the ability to eliminate free radicals in the body, and helping the body maintain its stability5.
The ability of quercetin to scavenging free radicals and binding transition metal ions makes quercetin capable of inhibiting lipid peroxidation, a process that can lead to various diseases in the body such as the formation of atherosclerotic plaques that can result in cardiovascular diseases and weaken the lipid membrane in the brain due to oxidative stress that can lead to neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease7.
2. Anti-inflammatory
Several testing models show that quercetin can reduce the expression of several cytokine genes by downregulating its main transcriptional factor, nuclear factor κB (NFκB)8. Several studies in vitro also show that quercetin can inhibit the growth of IL-8-induced LPS in lung A549 and the formation of lipopolysaccharide (LPS)-mediated tumor necrosis factor (TNF-α) in macrophages6.
3. Antimicrobial
Quercetin has shown bacteriostatic activity against several bacterial species including Helicobacter pylori, Salmonella enterica serotype Typhimurium, Micrococcus luteus, Yersinia enterocolitica, Pseudomonas aeruginosa, Escherichia coli, S. aureus, P. fluorescens, Campylobacter jejuni, and Staphylococcus epidermidis so it can be concluded that quercetin is more effective against gram-positive bacteria compared to gram-negative6.
Regarding its antifungal activity, quercetin shows ability to inhibit the growth of Candida species, Cryptococcus neoformans, Aspergillus species, and dermatophytes by inducing oxidative stress and altering the cell membrane composition in fungi6.
4. Anticancer
Quercetin has been found to induce apoptosis and cell cycle arrest in several cancer cell lines including breast, prostate, lung, and colon cancer6.
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References
1. Li, Y., Yao, J., Han, C., Yang, J., Chaudhry, M., Wang, S., Liu, H., & Yin, Y. (2016). Quercetin, inflammation and immunity. Nutrients, 8(3), 167. https://doi.org/10.3390/nu8030167
2. Singh, P., Arif, Y., Bajguz, A., & Hayat, S. (2021). The role of quercetin in plants. Plant Physiology and Biochemistry, 166, 10–19. https://doi.org/10.1016/j.plaphy.2021.05.023
3. Materska, M. (2008). Quercetin and its derivatives: chemical structure and bioactivity - a review. Polish Journal of Food and Nutrition Sciences, 58(4): 401-413
4. Kandemir, K., Tomas, M., McClements, D. J., & Capanoglu, E. (2021). Recent advances on the improvement of quercetin bioavailability. Trends in Food Science & Technology, 119, 192–200. https://doi.org/10.1016/j.tifs.2021.11.032
5. Yang, D., Wang, T., Long, M., & Li, P. (2020). Quercetin: Its main pharmacological activity and potential application in clinical medicine. Oxidative Medicine and Cellular Longevity, 2020, 1–13. https://doi.org/10.1155/2020/8825387
6. Aghababaei, F., & Hadidi, M. (2023). Recent advances in potential health benefits of quercetin. Pharmaceuticals, 16(7), 1020. https://doi.org/10.3390/ph16071020
7. Bentz, A. B. (2009). A review of quercetin: chemistry, antioxidant properties, and bioavailability — Journal of Young Investigators. Journal of Young Investigators. https://www.jyi.org/2009-april/2017/10/15/a-review-of-quercetin-chemistry-antioxidant-properties-and-bioavailability
8. Carrillo-Martinez, E. J., Flores-Hernández, F. Y., Salazar-Montes, A. M., Nario-Chaidez, H. F., & Hernández-Ortega, L. D. (2024). Quercetin, a Flavonoid with Great Pharmacological Capacity. Molecules, 29(5), 1000. https://doi.org/10.3390/molecules29051000
Editorial Team:
- Rafi Rif'atul Rizki, S.I.Kom.