A comprehensive quality control study of Salix alba L. stem bark: DNA barcoding, HPLC & HPTLC-based quantification, GC-MS & LC-MS profiling, elemental content and in vitro medicinal activities

The stem bark of Salix alba (SA) is extensively used in herbal medicine and nutraceuticals. The non-availability of quality standard available for SA stem bark in the Ayurvedic Pharmacopeia of India (API) leads inability to trace adulteration. In the current study, quality standard of SA stem bark has been developed in the interest of quality control, as per international standards including API parameters. The geographical changes could play a vital role in phytochemicals' and nutrients' variations. Hence, the samples from different geolocations and markets were analysed along with the cultivated plant sample. A comprehensive study including identification and authentication by DNA barcoding and pharmacognostic evaluation, physicochemical and phytochemical analysis by HPTLC was carried out. Moreover, a validated HPLC method was developed for the quantification of three phytochemicals (Salicin, Procyanidin B1 and Catechin) for the standardization of SA stem bark. The complete profiling of volatile metabolites and non-volatile metabolites was done by using GC-MS and LC-MS techniques, respectively. In ICP-OES based elemental analysis, heavy metals were observed below permissible limits, and SA stem bark has shown significant amount of essential metal ions like Na, Mg, Ca, Fe, Cu, and Zn. The observed total phenol content (TPC) and total flavonoid content (TFC) for all samples of SA stem bark ranged from 16.69 to 50.30 mg GAE/ g of wt. and 124.57 to 347.76 mg QCE/ g of wt., respectively. In DPPH assay, the observed IC50 values of SA stem bark ranged from 0.58 to 2.08 mg/mL. In antibacterial assay, SA stem bark has shown promising results against S. aureus and B. subtilis strains with inhibition zones of 20 +/- 4 mm. Overall, this is first report comprising of advanced quality standard and detailed standardization of SA stem bark with quantification of three important phytochemicals by HPLC along with the quantification of essential metal ions and other in vitro assays. Moreover, the study revealed that the fresh stem bark sample may contain significant content of phytochemicals and antibacterial activity.