Combination of microscopy and HPTLC to authenticate Securidaca longepedunculata Fresen. samples, one of the highest-selling medicinal plants on Lubumbashi markets

Introduction: Authentication of marketed medicinal plants is essential to ensure the safety of users of medicinal plants, i.e. ~79% of the population in Lubumbashi (DR Congo) [1, 2]. Best-selling species may be subject to adulteration or substitution, because of their economic importance. This study aims to authenticate the root samples of Securidaca longepedunculata Fresen, one of the most used species in this city.
Materials and Methods: A survey was conducted among the medicinal plant sellers in Lubumbashi’s markets and other public spaces, to identify the best-selling species. Microscopic characteristics of the powdered drug were combined with HPTLC fingerprints of the methanolic extracts to assess the identity of 31 purchased samples, by comparison with 2 authenticated reference samples. As abundant starch granules were detected in some samples, an enzymatic determination of starch was carried out.

Results: A total of 108 stalls were visited, and the S. longepedunculata root samples were found in 27.7 %. These roots were sold mainly in powder form, for the treatment of sexual weakness, typhoid fever, sinusitis, and constipation. From the 31 samples purchased from different herbalists, 23 (74 %) conformed with the microscopic elements observed in the 2 reference samples. The 8 samples different according to microscopy also showed major differences in their HPTLC profiles, for both polyphenols and terpenoids fingerprints. Among these samples, 6 showed differing HPTLC profiles, implying that they would be from 6 different adulterant species; 1 of them was also diluted with flour (57.6 % starch). From the 2 remaining samples, 1 presented chromatographic bands common with the reference samples but with additional spots, indicating either a contamination or a phytochemical variant; the second was diluted with flour (35.3 % starch). Results from this study indicate the substitution of S. longepedunculata in ¼ of the samples but obtained data did not allow to determine which were the adulterant species and whether substitution took place at harvest or in the market.

Conclusions: Some S. longepedunculata sellers encounter identification problems. Further analyses are needed to identify species confused or mixed with S. longepedunculata and the eventual risks involved.