Rapid multi-component quantification and quality assessment of Relinqing® granule (Polygonum capitatum) by near-infrared spectroscopy and chemometrics.

Relinqing® granule (RLQ), derived from Polygonum capitatum (P. capitatum), is traditionally used to treat urinary system disorders, but its quality control remains limited to gallic acid content in the 2020 Chinese Pharmacopeia. This narrow standard restricts comprehensive quality evaluation and broader use in functional foods and nutraceuticals. To address this issue, this study identified additional bioactive compounds and established a multi-marker quality control strategy. Twenty compounds were isolated from P. capitatum, among which gallic acid, ellagic acid, and quercetin showed significant anti-inflammatory activity through IL-6 inhibition. A near-infrared spectroscopy (NIRS) method combined with partial least squares (PLSs) regression was developed to predict the contents of these active compounds, using ultra-performance liquid chromatography (UPLC) as the reference. The resulting NIRS models showed high predictive accuracy, with correlation coefficients of 0.9000-0.9999, supporting their use for rapid, non-destructive, and cost-effective quality assessment of RLQ and related plant-derived products.