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Grapefruit seed extract (GSE), also known as citrus seed extract, is a liquid extract derived from the seeds, pulp, and white membranes of grapefruit. Self-made natural GSE processed in the laboratory without synthetic agents is prepared by grinding the grapefruit seed and juiceless pulp, then mixing with glycerin. Commercially available GSEs sold to consumers are made from the seed, pulp, glycerin (and in some cases synthetic preservatives) all blended together. GSE is sold as a food supplement and used in cosmetics because it is a claimed natural antimicrobial.

An early proponent was Jacob Harich (1919–1996). A long time promoter of GSE was Aubrey Hampton, the founder of Aubrey Organics. Some marketers of GSE affirm this extract to be a safe, natural, and effective preservative. This extract has been stated by some practitioners of alternative medicine to possess biological properties. GSE is promoted at health food shops and on the internet.

There are conflicting scientific demonstrations of the efficacy of GSE. Suspicions about the true nature of the active compounds in GSEs arose when synthetic additives were found in commercial products. Suspected counterfeit grapefruit seed extracts were adulterated with synthetic preservatives. When preservatives were not present in some of the extracts, laboratory tests found the natural extracts had no natural antimicrobial attributes of their own. Some manufacturers of GSE have stated that their extract has compounds nearly identical to benzethonium chloride, but a 2001 study supervised by chemist G. Takeoka has documented that commercial GSE preparations contain the synthetic compound benzethonium chloride that could not have been made from GSE.

History

The grapefruit is a subtropical citrus tree grown for its fruit which was originally named the "forbidden fruit" of Barbados. The fruit was first documented in 1750 by Rev. Griffith Hughes when describing specimens from Barbados. All parts of the fruit can be used. The fruit is mainly consumed for its tangy juice. The peel can be processed into aromatherapy oils and is also a source of dietary fiber. The seed and pulp, as by-products of the juice industry, are sold as cattle feed. Another application of the seed is in the production of grapefruit seed extract. Aubrey Hampton, founder of Aubrey Organics, has promoted citrus seed extract as a component of "Aubrey’s Preservative" for more than 25 years. Today, GSE is mostly promoted at health food shops and on the internet.

Efficacy

Anecdotal claims for an antimicrobial effect are based on abstract scientific experiments which show some antimicrobial activity in commercial grapefruit seed extracts and ethanol grapefruit seed extract but not natural GSE. The preliminary studies for the antimicrobial effect state that the Citricidal commercial brand of GSE was used for testing. There is considerable scientific evidence that the anti-microbial activity associated with grapefruit seed extract can be attributed to the contamination or adulteration of commercial GSE preparations with synthetic antimicrobials or preservatives. According to a 2001 study, branded commercial GSE preparations were contaminated with synthetic benzethonium chloride that was unlikely to have been made from grapefruit seeds. Some of the marketers claimed that their product did not contain benzethonium chloride and the error was due to the similarity in molecular weight of the quaternary ammonium compound which was formed through a proprietary manufacturing process. It is highly improbable that the preservative benzethonium chloride is formed during any extraction and/or processing of grapefruit seeds and pulp. Researchers conclusively demonstrated the presence of benzethonium chloride in commercial GSE using various analytical methods including HPLC, one- and two-dimensional NMR, PIXE analysis, and electrospray ionization MS. Another in vitro study claimed GSE had antibacterial properties. As with the branded in vitro test this extract was contaminated. The ethanolic grapefruit seed and pulp extract tested was prepared or contaminated with ethanol, a chemical solvent used in the extraction process. Ethanol, also known as ethyl alcohol, is effective in inhibiting bacteria.

Independent studies have shown some commercial preparations to contain the compound benzalkonium chloride (which is a synthetic antimicrobial commonly used in disinfectants and cleaning products), the related compound benzethonium chloride, the antibiotic triclosan, or the preservative methylparaben. Some samples were shown to contain up to 22% benzalkonium chloride by weight, despite the known allergenicity and toxicity of the compound at higher doses. These chemicals were not present in grapefruit seed extracts prepared in the laboratory, and GSE preparations without the contaminants were found to possess no detectable antimicrobial effect. Although citrus seed extract is sold in health food markets, there is no good evidence for any natural antimicrobial activity.

A study that examined the antiviral properties of GSE found that GSE had no efficacy as a disinfectant for feline calicivirus and feline parvovirus. Grapefruit seed extract has been advocated to be a powerful antimicrobial with proven activity against bacteria and fungi. However, independent studies have shown the efficacy of grapefruit seed extract as an antimicrobial is not demonstrated. Although citrus seed extract is claimed to be a highly effective plant-based preservative by some natural personal care manufacturers, studies asserted that the universal antimicrobial benefits associated with GSE are merely from the presence of synthetic preservatives. Natural GSE has no antimicrobial properties. Newer studies found many commercial grapefruit seed extracts contaminated with synthetic preservatives. In a 2007 study, the main synthetic antimicrobial agent identified in commercial GSE samples was benzethonium chloride. In a 2008 study, synthetic disinfectants such as benzethonium or benzalkonium chloride were identified in most of the commercial GSE products. In another 2008 study, suspected counterfeit products were determined to contain benzethonium chloride in grapefruit seed extract samples.

Methodology

Grapefruit seed extracts are added to cosmetics, food supplements, and pesticides for their antimicrobial effect, but suspicions about the true nature of the active compounds in GSEs arose when synthetic additives were found in commercial products. Various analytical methods were developed to determine the constituents or compounds in GSE samples which include particle-induced x-ray emission (PIXE), electrospray ionization mass spectrometry (ESI-MS), high performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR) analysis.

Phytochemicals

Analysis shows the phytochemicals of the seed extract and pulp are flavonoids, ascorbic acid (vitamin C), tocopherols, citric acid, limonoids, sterols, and minerals.

Preparations

Homemade pure GSE, processed without solvents, is prepared by grinding the grapefruit seed and juiceless pulp, then mixing with glycerin.

Commercially available GSE sold to consumers is made from the seed, pulp, glycerin, and synthetic preservatives all blended together.

Precautions

Grapefruit can have a number of interactions with certain drugs, increasing the potency of many compounds, including warfarin (coumadin). Grapefruit has components that inhibit the CYP3A4 enzyme in the intestine. Thus, it is this effect that increases the rate of absorption of several drugs. There are concerns about the safety of ingesting synthetic preservatives found in grapefruit seed extract.

Health claims and safety concerns

Although various health claims for using GSE are marketed in the dietary supplement industry, there is no scientific evidence from high-quality clinical research that it has any health effects, as of 2018. Phytochemicals in grapefruit seeds, particularly furanocoumarins and flavonoids, may cause adverse effects on health resulting from grapefruit–drug interactions that influence the intended therapeutic effects of some 85 prescription drugs. The main safety concern about GSE is inhibition of the liver enzyme, cytochrome P450, which controls liver metabolism of drugs; consequently its inhibition by GSE unpredictably increases the blood concentrations of prescribed drugs.

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• Antioxidants
• Dietary supplements
• Grapefruit
• Seeds