Characterization and technical evaluation of physicochemical properties of Tibetan medicine Zuotai via modern processing

Zuotai, known as the "king of medicines" in Tibetan pharmacology, is a crucial ingredient in precious formulations such as Seventy-flavor Pearl Pills. Traditional preparation of Zuotai is complex, time-consuming, labor-intensive, and poses significant toxicity risks. To address these challenges, our research team has modernized the process by replacing traditional tools with jacketed reactors and controlled heating, significantly reducing toxicity, shortening processing time from over 40 days to about 20 days, and enhancing reproducibility. In this study, five batches of Zuotai samples were characterized using X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). Results confirmed consistent physicochemical properties across all batches, dominated by HgS with excess sulfur. Safety evaluation via in vitro simulated gastric/intestinal fluid dissolution tests demonstrated that the soluble mercury release from modern-processed Zuotai was only 38.64 μg/g (0.0258% of total Hg) under the most stringent conditions (SGF with 10 mM L-cysteine, 37 °C, 24 h), corresponding to a daily intake of approximately 7.73 μg-only 18% of the FAO/WHO acceptable daily intake (43 μg/day), offering a standardized approach for Zuotai production.