Ultrasound-assisted enzymatic extraction and properties of polysaccharide from Nostoc commune

This study used Nostoc commune as the raw material to extract polysaccharides through ultrasound-assisted enzymatic extraction (UAE). A combined enzyme system consisting of pectinase, cellulase, and papain at a ratio of 1:1:1 was applied. Single-factor experiments were first conducted to evaluate the effects of solid-to-liquid ratio, enzyme dosage, enzymolysis temperature, enzymolysis time, ultrasound temperature, ultrasound power, and ultrasound duration on polysaccharide yield. Subsequently, the Plackett-Burman (PB) design was used to identify the three most significant factors affecting extraction efficiency. The steepest ascent method was then employed to determine the center point for the response surface methodology (RSM) experiments. Finally, the extraction process was optimized using the Box-Behnken (BB) design. The optimal extraction conditions were as follows: solid-to-liquid ratio of 1:80 g/mL, enzyme dosage of 0.3 g, enzymolysis temperature of 60 °C, enzymolysis time of 60 min, ultrasound power of 780 W, ultrasound time of 40 min, and ultrasound temperature of 50 °C. Under these conditions, the polysaccharide yield reached 34.11%. Structural characterization showed that polysaccharides obtained by UAE and HW displayed typical IR and NMR characteristic peaks with only minor structural differences, while revealing that those obtained by UAE had lower molecular weights, increased uronic acid content, and a similar monosaccharide composition primarily consisting of glucose, xylose, galactose, and glucuronic acid. Compared with HW, UAE significantly increased the polysaccharide yield by 16.68%, and improved antioxidant activity. These results indicate that UAE effectively improves both the extraction efficiency and bioactivity of N. commune polysaccharides. The findings provide technical support for their potential industrial application.