Detection of Adulterants of Buchu, an Important South African Medicinal Plant

Reviewed: Raman V, Sagi S, Galal AM, Avula B, Viljoen A, Khan IA. Adulteration in commercial buchu dietary supplements: analyses of commercial and authentic buchu samples and comparative studies of Agathosma betulina and Agathosma crenulata by microscopy and HPTLC. S Afr J Bot. 2015;100:122-131.

The leaves of buchu are highly valued in South Africa as a general tonic, diuretic, and for the treatment of urinary infections. Most of the commercial material is derived from Agathosma betulina (syn. Barosma betulina, Rutaceae), but A. crenulata (syn. B. crenulata) and A. serratifolia (syn. B. serratifolia) leaves also can be sold as buchu,¹ even though several authors caution about the use of A. crenulata due to its high content of pulegone.^2,3 Buchu has a long list of known adulterants,^3,4 but methods to authenticate buchu are scarce. The present paper presents two approaches for authentication of A. betulina and A. crenulata (no authenticated material from A. serratifolia was included in the study). All the materials were analyzed by light microscopy and high-performance thin-layer chromatography (HPTLC). While the three Agathosma species are readily differentiated by visual inspection (macroscopically), a distinction of powdered leaf material is more challenging. According to the microscopic evaluation, the leaf anatomy is very similar between A. betulina and A. crenulata; however, there was an abundance of minute (up to 10 x 5 μm in size) prismatic crystals of calcium oxalate in the lower epidermis of A. betulina. These crystals were not seen in A. crenulata. In addition, the length of the stomata was longer in A. betulina (32-41 μm) than in A. crenulata (24-34 μm).

The HPTLC analysis was carried out using methanol extracts of the various samples and rutin, kaempferol, and chlorogenic acid as reference standards. The two Agathosma species could be distinguished by a cluster of bands between response factor (Rf) 0.4 and 0.5 and the presence of chlorogenic acid in A. crenulata.

For the evaluation of commercial samples, 27 raw materials and finished products, including whole leaves, leaf powders, capsules, and one tea bag, were purchased online from various US websites (Bharathi Avula e-mail communication, July 22, 2015). Eleven of these samples were labeled as A. betulina, three as A. crenulata, one as A. serratifolia, and twelve other samples were not identified at species level and were sold as “buchu,” “Barosma spp.,” or “Agathosma spp.” The microscopy and HPTLC results did not match the authentic leaf material in 11 commercial samples, but the identity of the adulterant could often not be determined. Adulteration with senna (Senna alexandrina, Fabaceae) leaf was confirmed in one case and considered possible in three other samples based on the presence of the typical microscopic characteristics of senna leaves.

Comment: Buchu is one of the medicinal plants from South Africa that has been successfully commercialized outside the African continent. But the increased commercialization has led to concerns about the sustainability of the harvest, and to worries about substitution of the plant.⁵ Even within the areas where buchu is cultivated, harvesters are suspected of adding stones or mixing their buchu with vlieëbos leaves ahead of the weighing process to increase the weight to their bags.⁶ (Vlieëbos is a common name in Afrikaans used for several plant species, e.g., Myrsine africana [Myrsinaceae], Staavia glutinosa [Bruniaceae], and Saltera sarcocolla [Penaeaceae]; Leanne Dreyer e-mail communication, July 22, 2015.) Historically, A. betulina, A. crenulata, and A. serratifolia have been used interchangeably. If the whole leaf is present, the species can be visually distinguished by the leaf size, apex, and margins. The microscopy and HPTLC methods presented in this paper are useful tools to establish the correct identity of powdered buchu raw materials and can be easily implemented in a quality control setting. Used in combination, these methods represent a solid approach for the correct identification of this medicinal plant.

Additional experiments, e.g., the analysis of the commercial samples by HPLC-UV/Vis to find the characteristic senna anthraquinones (sennosides), might have been helpful to confirm the presence of senna in those cases where adulteration with this plant was considered possible. Thomas Brendler, CEO of the dietary supplement industry consulting firm Plantaphile, and director of the Association of African Medicinal Plants Standards (AAMPS), visited a buchu growing area a few months ago, and had the following comment: “General consensus from conversations was that supply from wild harvest and cultivation currently exceeds demand. Indeed, intentional adulteration at the supply end may be considered a historical problem at this point, referring to times when supplies were short and prices peaked. Of course, I cannot speak for all growers and suppliers, but only for what I have seen, that growers with any imaginable certification hold more stock than they can sell and, therefore, diversify into manufacturing of value-added products. With this said, buchu prices are still relatively high, which raises the possibility that the [observed adulteration] problem lies with the finished product manufacturers.”

References

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4.     Feldman HS, Youngken HW. A pharmacognostical study of buchu. J Am Pharm Assoc. 1944;33(8):277-288.

5.     Coetzee C. Buchu commercialization: South Africa. Elsenburg, South Africa: Agricultural Research Council. 1999;7:1-5. Available at: http://tcdc2.undp.org/GSSDAcademy/SIE/Docs/Vol7/Buchu_Commercialization_South_Africa.pdf. Accessed October 6, 2015.

6.     Williams S. Socio-economic aspects of the sustainable harvesting of buchu (Agathosma betulina) with particular emphasis on the Elandskloof community. MA thesis. Cape Town, South Africa: University of the Western Cape, Department of Geography & Environmental Studies, Faculty of Arts; 2005. Available at: http://etd.uwc.ac.za/xmlui/bitstream/handle/11394/193/Williams_MA_2005.pdf?sequence=1. Accessed October 6, 2015.