Mechanistic insight into the frequency-dependent ultrasound-assisted extraction of Rosa laevigata Polysaccharides: Structure, antioxidant activity, and process optimization

Rosa laevigata Michx. polysaccharide (RLMP) possess considerable bioactive potential; however, the frequency-dependent mechanisms underlying their ultrasound-assisted extraction (UAE) remain insufficiently understood. This study systematically investigated the influence of ultrasonic frequency on the extraction efficiency, structural characteristics, and antioxidant activity of RLMP, with the goal of optimizing the UAE process. Single-frequency ultrasound (SFU) at 20, 40, and 53 kHz and dual-frequency ultrasound (DFU) at 20/40 and 20/53 kHz were compared. Results demonstrated that 40 kHz SFU achieved the highest extraction yield, accompanied by higher glucose content, favorable molecular weight, and reduced protein contamination. In contrast, DFU treatments resulted in lower yields and elevated protein levels, indicating destructive wave interference rather than synergistic effects. Structural analyses further revealed that ultrasonic frequency significantly influenced monosaccharide composition, molecular weight distribution, and surface morphology, while the primary chemical structure remained unchanged. RLMP extracted at 40 kHz exhibited superior antioxidant activity, with more effective scavenging of diphenyl-1-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and superoxide anion radicals. Cellular antioxidant assays further confirmed its protective effects, showing a 42.83 % reduction in intracellular reactive oxygen species and enhanced superoxide dismutase activity. Comparative analyses demonstrated that UAE outperformed both hot-water extraction and microwave-assisted extraction under identical conditions. Process optimization using particle swarm optimization-support vector regression achieved higher predictive accuracy (R² = 0.9983) than response surface methodology (R² = 0.9816), identifying optimal extraction parameters: 34 min sonication time, 19 mL/g liquid-solid ratio, 180 W power, 41°C temperature, and 0.355 mm particle size, under which a maximum yield of 11.07 % was obtained. The purified RLMP-2 fraction, which contained 93.34 % total carbohydrates content, was characterized by nuclear magnetic resonance (NMR) as a heteropolysaccharide containing both ⍺- and β-glycosidic linkages. These findings provide theoretical guidance for the industrial-scale ultrasonic extraction of RLMP, though challenges including acoustic field uniformity, energy efficiency, and equipment scaling require systematic investigation before commercial implementation.