Effect of ultrasonic modification on physicochemical properties and bioactivity of polysaccharides from mycelium of Sanghuangporus vaninii

Sanghuangporus vaninii. mycelial polysaccharides (SIP) are difficult to apply in food and pharmaceuticals due to their high molecular weight and low bioavailability. Therefore, a method is urgently needed to reduce its molecular weight to improve its bioactivity. In this study, the response surface methodology was used to optimize the process conditions for ultrasonic modification of SIP (SIP concentration of 0.5 mg/mL, ultrasonic power of 510 W, and ultrasonic time of 3.5 h) to prepare ultrasonic-Sanghuangporus vaninii. mycelial polysaccharides (USIP). The analysis of physical and chemical properties and biological activities of SIP and USIP confirmed that compared with SIP, the total sugar, uronic acid, and sulfuric acid groups in USIP increased, while the protein content decreased slightly. Ultrasound did not alter the primary structure of the polysaccharides, which have longer side chains and more branched chains, and neither has a triple helical structure. The molecular weight of USIP is significantly lower and exhibits a degree of homogeneity compared to SIP, while the monosaccharide composition of USIP is altered. The apparent morphology of USIP is more fragmented than that of SIP, with the appearance of pores and grooves. The antioxidant and bacteriostatic properties of USIP were significantly improved compared to SIP, and ultrasound improved the biological activity of polysaccharides. These results indicate that ultrasound is an efficient and green polysaccharide modification method to produce value-added polysaccharides for use in functional foods or pharmaceuticals, providing a theoretical basis for applying SIP.