Botanical Adulterants Monitor: Issue 20, September 2020

Food Supplements Claiming to Contain Broccoli Sold Online Found to Contain Glucosinolates from Other Plants

Reviewed: Hensel A, Lechtenberg M. Nahrungsergänzungsmittel auf Brokkolibasis – wie sieht die Qualitätsituation aus? [German]^* Z Phytother. 2020;41(03):113-122.

Keywords: Adulteration, Brassica oleracea, Brassica oleracea convar. botyris var italica, Brassica spp., capillary electrophoresis, Sinapis alba, UHPLC-MS

There are several human clinical studies suggesting that use of broccoli (Brassica oleracea convar. botyris var italica, Brassicaceae) dietary and food supplements is beneficial, e.g., for cancer prevention, improving the elimination of airborne pollutants from the body, and gastritis. These beneficial properties have been attributed to broccoli’s content of glucosinolates such as glucoraphanin. Glucoraphanin can be converted into the isothiocyanate sulforaphane in the plant (e.g., by enzymatic cleavage after a plant is injured) or in the human body by gut microorganisms. Sulforaphane is the molecule that is most prominently linked to broccoli’s health benefits.

Quality control of plants containing glucosinolates is challenging because these compounds are ionic, thermally unstable, and have a poor chromophore. Liquid chromatography methods using ion pair or ion chromatography, combined with mass spectrometric detection, have often been the methods of choice. In this investigation, UHPLC-MS and capillary electrophoresis with ultraviolet detection (CE-UV) were used to analyze 4-hydroxyglucobrassicin, glucoerucin, glucoraphanin, glucoiberin, and sulforaphane in 13 commercial products claiming to contain broccoli extracts (n = 7), concentrates (n = 4), or powder (n = 2). One additional product claimed to contain “wild cabbage” powder, but since it is standardized to glucoraphanin, it was included in the analysis.

The authors found that only five products complied with the label regarding the concentrations of glucoraphanin. Two products were considered questionable due to the lower than expected glucoraphanin concentrations. Of these two products, one claimed 30 mg glucoraphanin but contained only 18 mg. The other product, a broccoli powder touted as a superfood, contained 0.08 mg glucoraphanin per 100 g powder, compared to the 6 mg/100 g freeze-dried powder which the authors prepared for comparison. The remaining seven products had major deficiencies; four contained little or no glucosinolates, while the other three contained glucosinolates different from those characteristic of broccoli flower head or seeds which are the plant parts highest in glucosinolates. In one product, the main compound was sinalbin, suggesting that the product was made from white mustard (Sinapis alba, Brassicaceae). Sinigrin and gluconapin, and gluconapin and glucobrassicanapin, respectively, were identified as the main glucosinolates in the other two preparations. Therefore, these products were made with Brassica species other than broccoli.

Comment: The results of this study unfortunately provide evidence that fraudulent companies once again are following the familiar pattern of replacing the labeled ingredient with presumably lower-cost materials having the same or similar chemical marker compounds. While substitution with extracts from other Brassica species or white mustard are readily detected using chromatographic fingerprints such as those used in this study, many suppliers may count on quality control laboratories using less specific tests, such as the determination of total glucosinolates by UV/Vis spectrophotometry or near-infrared assays. Given the fact that assays measuring total glucosinolates are easily fooled by adding non-broccoli glucosinolates, quality control laboratories measuring these compounds should use chromatographic (or other appropriate) methods to establish the authenticity of their ingredients.

References

1. Gallaher CM, Gallaher DD, Peterson S. Development and validation of a spectrophotometric method for quantification of total glucosinolates in cruciferous vegetables. J Agric Food Chem. 2012;60(6):1358-1362.
   
2. Mawlong I, Sujit Kumar MS, Gurung B, Singh KH, Singh D. A simple spectrophotometric method for estimating total glucosinolates in mustard de-oiled cake. Int J Food Prop. 2017;20(12):3274-3281.
3. DeClercq DR, Daun JK. Determination of the total glucosinolate content in canola by reaction with thymol and sulfuric acid. J Am Oil Chem Soc. 1989;66:788-791.
   
4. Hernández-Hierro M, Esquerre C, Valverde J, Villacreces S, Reilly K, Gaffney M, González-Miret ML, Heredia FJ, O’Donnell CP, Downey G. Preliminary study on the use of near infrared hyperspectral imaging for quantitation and localization of total glucosinolates in freeze-dried broccoli. J Food Eng. 2014;126:107-112.
   
5. Mailer RJ, McFadden A, Ayton J, Redden B. Anti-nutritional components, fibre, sinapine and glucosinolate content, in Australian canola (Brassica napus L.) meal. J Am Oil Chem Soc. 2008;85(10):937-944.