Dual-frequency ultrasound-assisted extraction of Pongamia pinnata (L.) Pierre polysaccharides: Process optimization, structural characterization, and anti-nephrolithiatic effects.

Pongamia pinnata (L.) Pierre is a versatile plant widely recognized for its medicinal, industrial, and ecological benefits. To facilitate its comprehensive utilization, this study employed dual-frequency ultrasound-assisted extraction (DUAE) combined with response surface methodology (RSM) to optimize the extraction process for polysaccharides from P. pinnata (PPP). Under the optimal conditions (ultrasonic power of 550 W, extraction time of 17 min, and liquid/solid ratio of 40 mL/g), the maximum yield of PPP was 9.17 ± 0.24 mg/g. PPP was further purified using ion-exchange and gel filtration chromatography to obtain an active polysaccharide PPPa. The structural characteristics and anti-nephrolithiatic activity of PPPa were then thoroughly evaluated. PPPa (Mw: 17.4 kDa) is an arabinoglucan with backbone consisting of → 4)-α-Glcp-(1 → residues, bearing two arabinan branches and one T-α-Glcp-(1 → monosaccharide chain. Notably, bioactivity assays showed that PPPa suppressed renal complement activation and coagulation cascades, reshaped the intestinal microbiota and its critical metabolites, and thereby markedly attenuated calcium oxalate stone formation in mice with glyoxylate-induced nephrolithiasis. Therefore, PPPa emerges as a novel polysaccharide exhibiting potent anti-nephrolithiatic activity, with substantial potential for use in functional foods and pharmaceutical formulations. This study establishes DUAE as a green, efficient, and scalable method for preparing bioactive natural products, and provides both a methodological framework and a scientific support for the subsequent development and exploitation of P. pinnata-derived polysaccharides.