Comparative supramolecular assemblies in traditional decoctions and formula granules of Magnolia officinalis–Glycyrrhiza uralensis: Roles of excipients and thermal history

Supramolecular assemblies (SMAs) formed during traditional decoction are increasingly recognized as an important physical-state contributor to the efficacy of traditional Chinese medicine (TCM), but whether these assemblies form reproducibly in Chinese herbal formula granules—and how excipients and thermal history modulate their behavior—remains poorly characterized. We compared the herb pair Magnolia officinalis – Glycyrrhiza uralensis prepared as a traditional co-decoction (MG) and as reconstituted formula granules (MGFG). SMAs were enriched by centrifugation followed by dialysis to yield MG-SMAs and MGFG-SMAs (0, 30, and 60 min re-decoction). An excipient-containing model was generated by adding dextrin, and the corresponding assembly-enriched colloidal fraction was operationally designated MGE-SMAs. We systematically compared assembly morphology and solution-phase colloidal properties using scanning electron microscopy (SEM) and dynamic light scattering (DLS) and probed the assembly microenvironment using Fourier-transform infrared spectroscopy (FT-IR) and ultraviolet–visible spectroscopy (UV–vis). Chemical profiling was performed by Ultra-high performance liquid chromatography with quadrupole time-of-flight mass spectrometry/mass spectrometry (UPLC-Q-TOF-MS/MS) combined with multivariate analyses, and representative constituents were quantified by High-performance liquid chromatography (HPLC). Anti-Staphylococcus aureus activity was evaluated by growth-inhibition curves (OD 600 ), MIC/MBC assays, and Live/Dead staining. The MG decoction presented a highly heterogeneous dispersion (1040.97 ± 91.00 nm; PDI 0.98 ± 0.02), whereas its centrifugation- and dialysis-derived colloidal fraction, MG-SMAs, exhibited a narrower nanoscale particle-size distribution (229.43 ± 3.27 nm; PDI 0.15 ± 0.07) with a similarly weakly negative ζ-potential and reduced conductivity, consistent with enrichment of a defined colloidal fraction. Addition of dextrin and reconstitution from granules increased dispersity (PDI 0.56–0.71) and reduced |ζ| (≈ −7 mV), indicating excipient- and processing-induced heterogeneity. Re-decoction was associated with time-dependent changes in the colloidal properties of MGFG-derived fractions. Compared with unheated MGFG-SMAs, MGFG-SMAs-30 exhibited a lower mean hydrodynamic particle size and PDI, while extending re-decoction to 60 min produced no further reduction in these parameters. UPLC-Q-TOF-MS/MS revealed broadly overlapping component coverage but a preparation-dependent redistribution of metabolites, and HPLC confirmed selective enrichment and depletion trends among marker compounds. Functionally, MG and MG-SMAs showed the same MIC against S. aureus (0.8 mg/mL), whereas excipient-containing systems required higher inhibitory concentrations; among granule-derived samples, MGFG-SMAs-30 produced the strongest inhibition. Although the excipients increased the concentration required for antibacterial inhibition, reheating partially improved the activity of the granule-derived preparations, suggesting that both composition and assembly state may influence bioactivity. This study established an analytical workflow integrating colloidal characterization with high-resolution chemical profiling to investigate how excipients and thermal history affect the formation and properties of assembly-enriched colloidal fractions derived from formula granules.