The power of grapefruit seed extract

The grapefruit, a popular breakfast fruit in the West, is often discarded for its bitter taste. Yet this bitterness that seeps into the pulp from the seeds has immense medicinal value and is included in several natural product formulations. The griffin+row Cleanse, Nourish and Enrich formulations are fortified with grapefruit seed extract. This is why it is necessary to find out the truth behind this citrus seed extract.

Introducing Citrus paradisi

Citrus paradisi is a naturally occurring hybrid of Citrus grandi (the pomelo) and Citrus sinensis (sweet orange). Commonly called the ‘grapefruit’ or Citrus racemose because of the clustered grape-like fruiting pattern, it is not as sweet as the parent orange. The fruit is also called Citrus maxima for its large size 1.

The origin of the grapefruit has been traced to the Caribbean island of Barbados. It appears that Christopher Columbus introduced the sweet orange as the first citrus species on the island in the 15th century. A couple of centuries later, the pomelo (Citrus grandi) landed there thanks to a Captain Shaddock of the erstwhile East India Company. The hybrid species that emerged retained the size and fruiting pattern of the pomelo, while keeping some of the sweetness of the orange. In 1828, the Scottish botanist James Macfayden christened the fruit Citrus paradisi, possibly after the beauty of the island. Whether or not Barbados is the Garden of Eden is debatable but early explorers who were wary of the bitter-sweet fruit went so far as to call it the ‘Forbidden Fruit’. Now, however, Barbados showcases the grapefruit as one of its ‘wonders’.  

Today, the fruit is cultivated in several countries that have at least some regions of tropical weather such as USA, Brazil and Israel. Grapefruit cultivation has been pursued seriously in the states of Florida and Texas in the USA. Here, the naturally occurring or radiation-induced mutants with redder and sweeter pulp have been selected for cultivation 2.

Traditional uses of Citrus paradisi

Like other citrus fruits that are indigenous to South Asia, Citrus paradisi was grown for its pulp. The bitter-sweet taste with a mild citrus tang added some complexity to salads or was simply eaten with salt and chilli powder. In traditional Chinese medicine, the fruit was considered to be a ‘cooling’ food for individuals with high rates of metabolism 3.

In the West, its popularity as a breakfast fruit rose when it was alleged to help in weight loss and have diuretic effects 4.

Grapefruit oil – like other citrus peel oils- has been widely used as an insecticide for its action against ticks, mosquitos and possibly bedbugs 6.

It took a Germany-educated Yugoslav physicist-turned-doctor Dr Jacob Harich to kick-start research into the processed fruit. Wondering at the bitterness of the seed, he proceeded to test the aqueous extract on various microbes after he moved to the USA. In the 1960s Dr Harich and his colleagues at the University of Florida found that the extract showed significant action on a broad spectrum of bacteria, fungi and protozoa. They went ahead and packaged the extract under the brand name Citricidal. Citricidal was demonstrated to be effective against more than 800 bacterial and viral strains, 100 strains of fungus and a large number of single or multicellular parasites. It was found that the extract destroyed microbes within a short time (15-20 minutes), making its bactericidal action comparable to that of known antibacterial compounds 7.

Subsequently, the US Department of Agriculture agreed to test the product in the 1980s and even recommended its use for the avian flu epidemic in 1984. This sparked an interest in the extract and several amateurish preparations flooded the market with tall claims. Unfortunately since these extracts were made in solutions that had several preservatives added, the veracity of the original claims was questioned.

Systematic studies carried out on the extract started appearing in scientific journals in the 1980s and 1990s. Again, the properties of grapefruit seed extracts were confounded by lack of a standard source of the same. Close on the heels of reports of efficacy against bacteria, fungi and viruses, there were counter claims of the properties being attributed to the preservatives (such as benzalkonium chloride or triclosan) in the preparations 8.  

The only universally consistent feature of grapefruit seed extract was its antioxidant properties. Hence, until recently it was only used as a safe alternative to synthetic preservatives in the food and cosmetic industry 9.

Bioactivity and associated components of the plant

The leaves and fruit of Citrus paradisi are used for their oil and phytonutrients.

  • Grapefruit leaf oil contains the terpenes sabinene and β-ocimene. A small percentage of p-cymene, terpinen-4-ol, linalool and limonene are also present which gives the oil a citrus fragrance 10.
  • Grapefruit oil is extracted from the rind of the fruit and marketed as an essential oil. The terpenes limonene (>97%) and myrcene (<2%) are the major constituents, with trace amounts of α-pinene, sabinene, geraniol, citronellal, linalool, decyl acetate, neryl acetate, terpinen-4-ol and nootkatone 11.
  • The reddish-pink grapefruit pulp is packed with lycopene, β- carotene, cryptoxanthin- β, polyphenols, flavonoids, vitamins A, C and B vitamins like folate, pyridoxine, riboflavin, niacin and pantothenic acid. Calcium, copper, magnesium, zinc, manganese, iron and phosphorus are the minerals that are present in significant quantities 12.
  • Grapefruit seed extract (GSE) is made from the residual pulp, mesocarp and seeds of the fruit. Besides ascorbic acid, vitamin E, citric acid and minerals, Grapefruit seed extract contains the following 13
  • Bioflavonoids– The major flavonoids present in Grapefruit seed extract are narigenin/naringin, isosacuranetin, neohesperidin, hesperidin, dihydrocampherol glycoside, poncirin, quercetin glycoside, campherol glycoside and apigenin rutinoside. These molecules have extremely low toxicity for humans and animals, making them effective antibacterial preservatives 14.
  • Limonoids – Limonoids are triterpenoid dilactones. The bitterness of citrus seeds is attributed to limonoids. More than 77% of the limonoids are neutral while 2 % are acidic limonoids. Limonin is the major neutral limonoid 15. Other limonoids include isoobacunoic acid and epiisoobacunoic acid, nomilinic acid and deacetylnomilinic acid 16. Limonoids have antimicrobial and antioxidant properties.

 Narigenin and Limonin: a spotlight on the main bioactive components

  • Narigenin is a flavonone.  

Narigenin is found more in the pulp than the seeds of grapefruit. This flavonone is responsible for the slightly bitter taste of the fruit pulp. Narigenin is an anti-oxidant and has significant antibacterial, antifungal and antiviral activity. Naringin, the glycosidated form of narigenin, also protects the skin against harmful UV rays 17.

  • Limonin is a neutral limonoid.  

Limonin confers the bitter taste to the seed of the grapefruit. The bitterness is less when it is attached to a sugar (as it is in the figure). At the acidic pH of citrus juice, the sugar moiety is lost and the bitterness increases, a problem that is faced when the fruit is processed for packaged juice.

Limonin has a long half-life in blood and can be detected even 24 hours after consumption of the citrus fruit extract. Limonin is a powerful antioxidant and has been shown to have anti-cancer effects by inhibiting the enzyme glutathione-S- transferase 18.

General health benefits and uses of grapefruit seed extract:

Fruit that do not have an appreciable quantity of pulp are processed to generate Grapefruit seed extract (GSE). The inedible white mesocarp along with the pulp and seeds are extracted in a mixture of ethanol, glycerine and water. These days organically grown Citrus paradisi is used for GSE preparation and a minimum of ethanol is used for extraction to ensure maximum efficacy.

Pharmacological uses of grapefruit seed extract:

  • Antioxidant effects: The presence of flavonoids and limonoids in GSE makes the extract a powerful antioxidant. This not only helps in increasing the shelf-life of cosmetic formulations, but also penetrates the skin to decrease free-radical formation and signs of ageing.
  • Antibacterial activity: In vitro studies have shown a potent antibacterial activity of grapefruit seed extract against a wide spectrum of bacteria including Staphylococcus (which causes pus formation in pimples), Streptococcus spp, Enterococcus and Bacillus cereus. It is most effective against enteric pathogenic bacteria like E.coli, Shigella spp., Salmonella spp., Pseudomonas, Klebsiella etc. 19. GSE added to drinking water is used as a prophylactic against traveller’s diarrhoea.
  • Antifungal activity: GSE is also effective against yeast 19 and fungi.
  • Wound healing activity: GSE has been shown to decrease the intensity of gastric lesions in laboratory animals 20.
  • Anticancer activity: Citrus limonoids have been shown to have anti-cancer activity by inducing detoxifying enzymes like glutathione-S-transferase 21.
  • Use in the cosmetic industry: Grapefruit seed extract is used as a natural antioxidant in cosmetic formulations. Incorporating the extract in face washes, soaps and lotions also confers some protection against pimples.

Botany and grow it yourself

The grapefruit, like the pomelo is one of the largest fruits of the citrus family and can easily weigh 1-1.5 kg. The tree belongs to the family Rutaceae and grows to a height of 15-30 ft. The leaves are dark green and glossy, 5-20 cm long and 2-15 cm wide. The white flowers that bloom in clusters of 2-8 at the end of the branches have a beautiful citrus fragrance. The large fruit that form from the flowers often weigh down the branches. The fruit are green when unripe and slowly turn yellow upon ripening. The essential oil is extracted from the rind of the fruit.

Propagation is by seeds and cuttings. Grapefruit grows well in tropical to semi-tropical climates 1.

Glossary

Polyphenols: A class of naturally occurring compounds that contain several phenolic groups linked together. Derived from plants, polyphenols are important antioxidant compounds. Tannin (present in tea) is one of the best-known polyphenols.

Flavonoids: Flavonoids are a subclass of polyphenols that have two six-membered carbon rings and one oxygen- containing heterocyclic ring. The name is derived from the typically yellow colour of the compounds. Flavonoids are present in plants and fungi. They have been shown to have antimicrobial, anticancer and antioxidant activities.

Limonoids: Limonoids belong to a class of furanolactones, with four six- membered and one five- membered oxygen containing aromatic rings fused together and attached to cyclic sugars (lactones). Limonoids are secondary metabolites that are present largely in citrus fruits and neem. The primary function of limonoids is to protect the seed and fruit from microbial attack.


References

  1. Scora R, Kumamoto J, Soost R. and Nauer E. (1982). Contribution to the origin of the grapefruit, Citrus paradisi (Rutaceae). Systematic Botany,7(2): 170-177.
  2. Texas grapefruit history. Retrieved from http://www.texasweet.com/texas-grapefruits-and-oranges/texas-grapefruit-history/ (29th June, 2017).
  3. Lu Y, Zhang C, Bucheli P, Wei D. (2006). Citrus flavonoids in fruit and traditional Chinese medicinal food ingredients in China. Plant Foods & Human Nutrition. 61(2): 57-65.
  4. The benefits of Grapefruit, the “Fruit of Paradise” (2008). Retrieved from https://www.findatopdoc.com/Healthy-Living/The-Benefits-of-Grapefruit-the-Fruit-of-Paradise (30th June, 2017).
  5. Substances that give grapefruit its flavour and aroma could give insect pests the boot. (2013). Retrieved from https://www.acs.org/content/acs/en/pressroom/newsreleases/2013/september/substance-that-gives-grapefruit-its-flavor-and-aroma-could-give-insect-pests-the-boot.html (30th June, 2017).
  6. Grapefruit seed. (2015). Retrieved from http://www.herbalextractsplus.com/grapefruit-seed.html (9th August, 2017).
  7. Citricidal grapefruit seed extract. Undated. Retrieved from https://www.nutriteam.com/citricidal (9th August, 2017).
  8. Cardellina II JH. (2017). Grapefruit seed extract – laboratory guidance document. Retrieved from http://cms.herbalgram.org/BAP/LGD/ABC-LGDs-GFSE-CC-05092017-v5.pdf (9th August, 2017).
  9. Gavura S. (2016). Not natural, not safe: Grapefruit Seed Extract. Retrieved from https://sciencebasedmedicine.org/not-natural-not-safe-grapefruit-seed-extract/ (9th August, 2017).
  10. Ekundayo O, Bakare O, Adesomoju A and Stahl-Biskup E. (1991). Composition of the leaf oil of grapefruit (Citrus paradisi). Journal of Essential Oil Research.3(1): 55-56.
  11. Ou M-C, Liu Y-H, Sun Y-W and Chan C-F. (2015).The composition, antioxidant and antibacterial activities of cold-pressed and distilled essential oils ofCitrus paradisi and Citrus grandis (L.) Osbeck. Evidence-Based Complementary and Alternative Medicine : eCAM2015, 804091. http://doi.org/10.1155/2015/804091
  12. The benefits of Grapefruit, the “Fruit of Paradise” (2008). Retrieved from https://www.findatopdoc.com/Healthy-Living/The-Benefits-of-Grapefruit-the-Fruit-of-Paradise (30th June, 2017).
  13. Grapefruit seeds. (2017). Retrieved from http://www.chinese-herbs.org/grapefruit-seeds/ (9th August, 2017).
  14. Heggers JP, Cottingham J, Gusman J, Reagor L, McCoy L, Carino E, Cox R, Zhao JG. (2002). The effectiveness of processed grapefruit-seed extract as an antibacterial agent: II. Mechanism of action and in vitro toxicity. Journal of Alternative and Complementary Medicine 8: 333-340.
  15. Hasegawa S, Bennett RD and Verdon CP. (1980). Limonoids in citrus seeds. Journal of agricultural and food chemistry 28: 922-925.
  16. Ozaki Y, Fong CH, Herman Z, Maeda H, Miyake M, Ifuku M and Hasegawa S. (1991). Limonoid Glucosides in Citrus Seeds. Agricultural and biological chemistry, 55 (1): 137-141.
  17. Ren X, Shi Y, Zhao D, Xu M, Li X, Dang Y, Ye X.(2016). Naringin protects ultraviolet B-induced skin damage by regulating p38 MAPK signal pathway. Journal of Dermatological Sciences. 82(2):106-114.
  18. Limonin functions. (2017). Retrieved from http://www.limonin.com/functions.php (11th August, 2017).
  19. 19.Cvetnij Z and Vladimir-Knezevic S. (2004). Antimicrobial activity of grapefruit seed and pulp ethanolic extract GSE has been recommended as a prophylactic for traveller’s diarrhoea. Acta Pharmacologia 54: 243-250.
  20. Brzozowski T, Konturek PC, Drozdowicz D, Konturek SJ, Zayachivska O, Pajdo R, Kwiecien S, Pawlik WW, Hahn EG. (2005). Grapefruit-seed extract attenuates ethanol-and stress-induced gastric lesions via activation of prostaglandin, nitric oxide and sensory nerve pathways. World Journal of Gastroenterology 11(41):6450-6458.
  21. Perez JL, Jayaprakasha GK, Cadena A, Martinez E, Ahmad H and Patil BS. (2010). In vivo induction of phase II detoxifying enzymes, glutathione transferase and quinone reductase by citrus triterpenoids. BMC Complementary and Alternative Medicine,10, 51. http://doi.org/10.1186/1472-6882-10-51.