Marker-based standardization of Terminalia arjuna bark for the detection of probable adulterants by quantitative high-performance thin-layer chromatography

Abstract

The bark of Terminalia arjuna (Combretaceae) is traditionally used for cardio-protective and cardio-strengthening properties worldwide. It is rich in glycosides, triterpenoids, flavonoids, tannins, sitosterol, and minerals, it is extensively used for its potent medicinal properties, and, in turn, it has been often adulterated with the barks of Terminalia alata, Terminalia bellirica, Terminalia calamansanai, Terminalia catappa, Terminalia chebula, Terminalia myriocarpa for commercial purposes. However, these adulterants and substitutes considerably differ in their phytochemical profile and medicinal properties, which further lead to the loss of major therapeutic effect of T. arjuna bark-based products. The main aim of the present research was to identify the presence of the major constituents arjunetin and arjungenin as marker compounds in representative plant bark and the detection of probable adulterants in the bark of T. arjuna powder. Investigation was carried out on stem bark powders from T. arjuna, T. bellirica, T. calamansanai, and T. chebula using the high-performance thin-layer chromatography (HPTLC) technique: the method exploited pre-coated silica gel TLC aluminum plates 60F₂₅₄ on aluminum sheets (10 × 20 cm) as the stationary phase, while the mobile phase consisted of toluene‒ethyl acetate‒formic acid (5:4:1, V/V). Densitometric analysis of arjungenin and arjunetin was carried out in respective absorbance modes at 420 and 475 nm. The presence of arjungenin and arjunetin was confirmed by the ultraviolet (UV) exposure of all TLC patterns of samples compared with standards within R_F 0.43 and 0.67, respectively. The regression mode for the calibration plots arjunetin and arjungenin showed good linear relationship (i.e., R² = 0.9921, SD = 3.53% and R² = 0.98687, SD = 13.77%, respectively), in the concentration range of 100–1000 ng/spot. Adulteration was assessed on the basis of detection of additional peaks and size variation of standard peaks in mixed extracts. The findings may be useful in the identification as well as quality evaluation technique for herbal drugs. However, major lacunae still lack phytochemical standardization of bark extracts to identify and clarify individual active principles/compounds with exact phytochemicals responsible for these curative effects of T. arjuna, T. bellirica, T. calamansanai and T. chebula. Thus, further investigations are required.