Grapefruit Seed Extract


David McCluggage, D.V.M., C.V.A.

Grapefruit Seed Extract is commonly reported to have powerful antimicrobial activity. Some manufacturers claim that it is highly effective in a variety of microbial infections, including these organisms:

  1. Fungi
    1. Aspargillosis
    2. Candida albicans
    3. Trichophyton sp (ringworm)
  2. Bacteria
    1. Klebsiella
    2. Pseudomonas
    3. Escherichia coli (E. coli)
    4. Clostridium
    5. Salmonella

Companies that manufacture grapefruit seed extract products claim to have extensive research proving their beneficial effects. Some companies even publish extensive "scientific" evaluations of their products' effectiveness on their web pages.

However, when carefully analyzed and studied, grapefruit seed extract products appear to have little or no antimicrobial properties. Even more curious is the fact that almost all of the grapefruit seed extract products on the market contain preservatives that are intended to prevent the growth of bacteria and fungi! This would make one wonder why, if these extracts were so powerful, the full strength concentrate (which should be far more effective in preventing microbial growth than the label recommended diluted dose) needs any preservative at all?

Also, when WellVet.com evaluated the claims of one of the companies, the parts per million (ppm) dose needed to control the various organisms in the sensitivity study were actually remarkably high. In reality, it would be impossible to achieve blood levels approaching those needed for the product to work. For example, to achieve control of Pseudomonas, 20,000 PPM was needed to achieve effective control. It is quite impossible to reach such concentrations in the bird's body, let alone consider what toxic damage might occur due to the presence of the preservatives in the product.

It seems to us at WellVet.com that the entire effectiveness of grapefruit seed extract is due totally to the presence of the preservatives, and the grapefruit seed extracts have no antimicrobial effects on their own.

For those who would like to look further into this issue, we offer the following abstracts of scientific studies involving grapefruit seed extracts:

These abstracts are from PubMed.

Von Woedtke T, Schluter B, Pflegel P, Lindequist U, Julich WD. Institute of Pharmacy, Ernst Moritz Arndt University, Greifswald, Germany. Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained. Pharmazie 1999, Jun:54(6):452-6


The antimicrobial efficacy as well as the content of preservative agents of six commercially available grapefruit seed extracts were examined. Five of the six extracts showed a high growth inhibiting activity against the test germs Bacillus subtilis SBUG 14, Micrococcus flavus SBUG 16, Staphylococcus aureus SBUG 11, Serratia marcescens SBUG 9, Escherichia coli SBUG 17, Proteus mirabilis SBUG 47, and Candida maltosa SBUG 700. In all of the antimicrobial active grapefruit seed extracts, the preservative benzethonium chloride was detected by thin layer chromatography. Additionally, three extracts contained the preserving substances triclosan and methyl parabene. In only one of the grapefruit seed extracts tested no preservative agent was found. However, with this extract, as well as with several self-made extracts from seed and juiceless pulp of grapefruits (Citrus paradisi), no antimicrobial activity could be detected (standard serial broth dilution assay, agar diffusion test). Thus, it is concluded that the potent as well as nearly universal antimicrobial activity being attributed to grapefruit seed extract is merely due to the synthetic preservative agents contained within. Natural products with antimicrobial activity do not appear to be present.

Xiong H, Li Y, Slavik MF, Walker JT. Spraying chicken skin with selected chemicals to reduce attached Salmonella typhimurium.
Department of Biological & Agricultural Engineering, University of Arkansas, Fayetteville 72701, USA. J Food Prot 1998 Mar;61(3):272-5


Aqueous solutions of 5% and 10% trisodium phosphate (TSP), 0.1% and 0.5% cetylpyridinium chloride (CPC), 1% and 2% lactic acid (LA), and 0.1% and 0.5% grapefruit seed extract (DF-100) were evaluated in prechill spraying for reducing Salmonella typhimurium attached on chicken skins. Chicken skins were inoculated with S. typhimurium and then sprayed with the selected chemical solutions for 30 sec at 206 kPa and 20 degrees C. After chemical spraying, the skins were rinsed by spraying tap water for 30 sec. Each skin was stomached in buffered peptone water (BPW) for 1 min. The stomaching water was then diluted serially, inoculated onto both xylose lysine tergitol (XLT4) agar and Aerobic Plate Count (APC) Petrifilm, and incubated for 24 hr at 37 degrees C. The results showed that the numbers of Salmonella on the chicken skins after the chemical spraying were significantly lower than those without spray (P [[lt]] 0.05). The CPC reduced Salmonella by 1.5 to 1.9 log10. TSP resulted in a 2.1 to 2.2 log10 reduction of Salmonella and DF-100 produced a 1.6 to 1.8 log10 reduction of Salmonella. The LA had a number of Salmonella with a 2.2 log10 reduction. The 0.5% CPC resulted a significantly greater reduction in Salmonella than 0.1% CPC. There were no significant differences in Salmonella reduction between different concentrations of the other three chemicals.

Sakamoto S, Sato K, Maitani T, Yamada T. [Analysis of components in natural food additive "grapefruit seed extract" by HPLC and LC/MS] [Article in Japanese] Eisei Shikenjo Hokoku 1996;(114):38-42


The components in a commercial natural food additive, [[quot]]Grapefruit seed extract[[quot]], and the ethanol extract of grapefruit seeds were analyzed by HPLC and LC/MS. The HPLC chromatogram of the commercial grapefruit seed extract was quite different from that of the ethanol extract of grapefruit seeds. Three main peaks were observed in the chromatogram of the commercial grapefruit seed extract. By comparison of the retention times and the absorption spectra with those of authentic samples, two peaks were ascribed to methyl-p-hydroxybenzoate and 2,4,4'-trichloro-2'-hydroxydiphenylether (triclosan). Triclosan was also identified by LC/MS by using the negative electrospray ionization method.

Calori-Domingues MA, Fonseca H. Laboratory evaluation of chemical control of aflatoxin production in unshelled peanuts (Arachis hypogaea L.). Departamento de Ciencia e Tecnologia Agroindustrial, Escola Superior de Agricultura, Universidade de Sao Paulo, Piracicaba, Brazil. Food Addit Contam 1995 May-Jun;12(3):347-50


Propionic acid (ammonium salt) at 3000 mg/kg (PA1) and 5000 mg/kg (PA2) of unshelled peanuts (UP); grapefruit seed extract at 5000 mg/kg (GF1) and 10,000 mg/kg (GF2); sodium orthophenylphenate at 2500 mg/kg (SOP1) and 5000 mg/kg (SOP2); thiabendazole 1000 mg/kg (TBZ1) and 5000 mg/kg (TBZ2) were studied in the laboratory, to verify their efficiency in controlling fungal growth and aflatoxin (AF) production on moist UP (16-18% moisture content). Moist UP were put into polyethylene bags with cotton plugs and incubated at 30 +/- 2 degrees C for 28 days. Treatments were considered efficient when the AF content (B1 + G1) remained under 30 micrograms/kg. PA1 treatment was efficient until 14 days of incubation and PA2 during the whole incubation period (28 days). All other treatments were not efficient, showing AF contents from 150 to 108,333 micrograms/kg during the incubation periods. Propionic acid, used as ammonium propionate, at 5000 mg/kg shows promise in controlling aflatoxin production when applied to moist unshelled peanuts.

Ranzani MR, Fonseca H. Mycological evaluation of chemically-treated unshelled peanuts. Departamento de Ciencia e Tecnologia Agroindustrial, Universidade de Sao Paulo, Piracicaba, Brazil. Food Addit Contam 1995 May-Jun;12(3):343-6


In the present work, the effect of propionic acid (ammonium salt) at 3000 mg/kg of unshelled peanuts (PA1) and at 5000 mg/kg (PA2), grapefruit seed extract at 5000 mg/kg (GF1) and 10,000 mg/kg (GF2), sodium orthophenylphenate at 2500 mg/kg (SOP1) and at 5000 mg/kg (SOP2) and thiabendazole at 1000 mg/kg (TBZ1) and at 5000 mg/kg (TBZ2) was studied for controlling total and potentially aflatoxigenic fungi in unshelled peanuts (UP). Samples of sound mature UP were moistened by adding water and kept refrigerated till they reached 16% moisture. The samples were then sprayed with the chemical solutions and incubated at 30 +/- 2 degrees C for 28 days. Control samples were sprayed with water. An evaluation of total and aflatoxigenic fungi was made, in pods of UP and in kernels obtained aseptically, before and at 7, 14, 21 and 28 days of incubation, by serial dilution in culture media Dichloran Rose Bengal Chloramphenicol (total fungi count) and in Aspergillus flavus parasiticus Agar (potentially aflatoxigenic count). In relation to the period and conditions of this experiment the overall best treatment was PA2, when the lowest average value of total and aflatoxigenic fungi were obtained in UP and were maintained in its kernels. Although SOP2 treatment could control fungal contamination in pods, it was not effective in controlling contamination through the kernels. The other treatments were ineffective.