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Grapefruit seed extracts marketed as environmentally friendly agricultural pesticides for farming were adulterated with synthetic antimicrobial agents, say Austrian researchers, intensifying the arguments regarding their potential benefits. If you enter grapefruit extract into your internet search engine, you might be surprised to find that there are hundreds of hits. This is because grapefruit extract, or more correctly, grapefruit seed extract (GSE), is one of the more popular natural remedies, having antimicrobial and antioxidant properties. There are claims that it is effective against more than 800 bacteria, yeast, fungi and viruses, even HIV. The extract is prepared by grinding dried grapefruit seeds and membranes into a fine powder, removing the pectin and fibre, and dissolving the residue in glycerine to reduce the bitter taste. Upon heating with food-grade ammonium chloride and ascorbic acid, the polyphenolic compounds present are converted into quaternary ammonium compounds, which, it is claimed, impart the antimicrobial properties. So, in fact, GSE is not a purely natural formulation. The diverse powers of GSE in human health extend to such areas as treating osteoporosis, stomach ulcers, head lice and skin irritations. But beware those of you who are considering trying it out: grapefruit juice and GSE are known to increase the levels of quite a number of prescription drugs in the blood stream, causing unpleasant side effects. I know this from personal experience. No-one believes you when you fall over in the university bar and claim not to have been drinking alcohol but my antibiotics and two glasses of grapefruit juice were the real reason. Well, that's my story. Away from personal health, GSE is also used in cosmetics, as a household germicide, and for prolonging the shelf life of fruits and vegetables. It is also employed as an eco-friendly pesticide for farming. However, despite the broad claims of GSE efficacy, there have been some doubts expressed recently as to the nature of the active ingredients. These were compounded when some commercial GSEs were found to be adulterated with synthetic preservatives such as methyl paraben and benzethonium chloride. With this in mind, researchers in Austria from the University of Innsbruck have tested a series of commercial products for the eco-farming market that claimed to contain GSE. Markus Ganzera and colleagues used a combination of HPLC with UV detection and electrospray ionisation LC/MS. In the first instance, they identified 18 preservatives that could be used to modify the natural GSE formulations. These included esters of benzoic and 4-hydroxybenzoic acids, salicylic acid, chlorhexidine and the benzalkonium chlorides, with the C12, C14 and C16 homologues. The team recognised that there is no established HPLC method for separating this diverse group of compounds so devised and optimised a new procedure. The final method employed a 15-cm C8 column operated at 40 °C with a mobile phase gradient of trifluoroacetic acid in acetonitrile-isopropanol. Under these conditions, the 18 preservatives were baseline separated, although some peaks eluted very closely to others. With UV detection at 205 nm, quantification was attainable over a large linear range. However, due to the similarity in retention times of some of the preservatives, further confirmation of their identity was required, so the team extended the HPLC method to LC-DAD-MS using the same HPLC separation conditions. With positive electrospray ionisation, all of the compounds could be unambiguously confirmed with confidence. The various GSEs were then analysed. The liquid GSEs were simply diluted with methanol and the single powdered sample was dissolved in methanol. All were subjected to analysis by HPLC and LC/MS with selected ion monitoring to verify the presence of the preservatives. Nine GSEs were examined and seven contained artificial preservatives. Some contained only benzethonium chloride, in amounts ranging from 2.5-176.9 mg/mL. The other positive samples contained no benzethonium chloride but were adulterated with a combination of several preservatives, the most abundant being benzalkonium chlorides (total of C12-C16 homologues 138.2-236.3 mg/mL). Smaller amounts of methyl 4-hydroxybenzoate (9.8-217.9 mg/mL) and propyl 4-hydroxybenzoate (5.0-9.1 mg/mL) made up the remaining adulterants. The researchers argue that it is highly unlikely that these additives would be formed in the juice extraction process, so they must have been added by the manufacturers. As well as the fact that they violate the principles of ecofarming and represent fraudulent behaviour, some of the preservatives are known to be toxic to animals and humans. Interestingly, one of the GSEs contained no grapefruit extract but comprised a combination of other herbal extracts: Equisetum arvense (field horsetail), Arnica montana (arnica) and Thymus vulgaris (garden thyme). The test samples, supplied by an Italian agricultural research institute, represent a tiny proportion of commercial GSEs and it will be interesting to extend the study to see how many more "natural" GSEs are, in fact, tainted. The new HPLC and HPLC/MS methods will enable this to be achieved. Related links:
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 Commercial grapefruit seed extracts contain artificial additives |
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