Well! <cracking my fingers and grinning!> Here are abstracts from several research papers, Saponista. The first is probably the most damning evidence about GSE.
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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.
Source: Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained. von Woedtke T1, Schlüter B, Pflegel P, Lindequist U, Jülich WD.
http://www.ncbi.nlm.nih.gov/pubmed/10399191
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Commercial grapefruit seed extracts (GSE) were extracted with chloroform. The solvent was evaporated, and the resulting solid was subsequently analyzed by high-performance liquid chromatography, electrospray ionization mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis (by proton-induced X-ray emission [PIXE] analysis).
The main constituent was identified as benzethonium chloride, a synthetic antimicrobial agent commonly used in cosmetics and other topical applications. This compound comprised 8.03% (n = 2) of the liquid GSE sample. Higher amounts of benzethonium chloride were found in powder GSE samples.
Source: Identification of benzethonium chloride in commercial grapefruit seed extracts. Takeoka G1, Dao L, Wong RY, Lundin R, Mahoney N.
http://www.ncbi.nlm.nih.gov/pubmed/16159196
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Grapefruit seed extract (GSE), derived from the seeds of grapefruit (Citrus paradisi MCAF.), is listed as a natural food additive in Japan. Products containing GSE are used as disinfectants made from only natural sources, especially after Japanese researchers found that GSE prevents the growth of norovirus.
On the other hand, recent overseas studies indicated that synthetic disinfectants, such as benzalkonium and benzethonium chlorides, were present in some commercial GSE products. To confirm the quality of commercial GSE products available in Japanese markets, we carried out comprehensive research to identify the major constituents of commercial GSE products which are used as food additives (13 products from 6 manufacturers), dietary supplements (5 products from 4 manufacturers), cosmetic materials (16 products from 10 manufacturers) and disinfectant or deodorant sprays (7 products from 7 manufacturers).
By means of NMR and LC/MS analysis, synthetic disinfectants such as benzethonium or benzalkonium salts were detected in most of the commercial GSE products.
Source: Survey of synthetic disinfectants in grapefruit seed extract and its compounded products. [Article in Japanese] Sugimoto N1, Tada A, Kuroyanagi M, Yoneda Y, Yun YS, Kunugi A, Sato K, Yamazaki T, Tanamoto K.
https://www.ncbi.nlm.nih.gov/pubmed/18344660
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More scholarly references are listed here:
https://en.wikipedia.org/wiki/Grapefruit_seed_extract
