Ultrasound-Assisted Flash Extraction of Juglans cathayensis Polysaccharides and Their Phosphorylation Treatment: Structural Characterization, Antioxidant, and Hypoglycemic Activities.

Traditional methods for extracting Juglans cathayensis polysaccharides (JCP) suffer from low yield and poor efficiency; moreover, the biological activity of these natural polysaccharides is often limited, which severely hampers their functional development and application. Juglans cathayensis (JC) is a plant with medicinal and edible values. This study adopted the ultrasound-assisted flash extraction (UAFE) method to isolate polysaccharides from the fruits of JC. Response surface methodology (RSM) was employed to optimize the extraction conditions. Meanwhile, the purified polysaccharides (JCP) were subjected to phosphorylation modification, and the structural characteristics and biological activities of the polysaccharides before and after modification were systematically compared. Results showed that the optimal extraction conditions were: ultrasonic power 400 W, temperature 60°C, extraction time 90 min, liquid-solid ratio 40:1 mL/g, flash extraction voltage 120 V, flash extraction time 120 s, and flash extraction performed twice. Under these conditions, after isolation and purification, the crude polysaccharide achieved a yield of 27.74% with a purity of 70.89%. The JCP was chemically modified to obtain its phosphorylated derivative (JCP-P). The results showed that, after phosphorylation modification, the molecular weight (Mw) of the polysaccharide decreased, the particle size reduced, the dispersion and thermal stability significantly improved, the triple-helix structure was retained, and the microscopic morphology changed from a porous network structure to a dense lamellar structure. Furthermore, in cell-based assays, JCP-P showed significantly better scavenging abilities against DPPH, ABTS, hydroxyl, and superoxide anion radicals, superior protective effects against H2O2-induced oxidative damage in HepG2 cells, stronger inhibitory activities against α-amylase and α-glucosidase, and greater promoting effects on glucose consumption and hepatic glycogen synthesis in insulin-resistant HepG2 cells, compared with JCP. These findings indicate that UAFE can efficiently prepare JCP, and phosphorylation modification can significantly enhance their antioxidant and in vitro hypoglycemic activities, providing a theoretical basis and technical support for the high-value utilization of JC resources.