Effects of Different Extraction Processes on Structural Characteristic and Immunomodulatory Activity of Pleurotus eryngii Polysaccharide

Hot water extraction (H), ultrasonic extraction (U) or ultrasonic-assisted hot water extraction (U + H) was used to extract polysaccharides from Pleurotus eryngii, which were then evaluated for physicochemical and structural characteristics and immunomodulatory activity. Results indicated that all three polysaccharides showed absorption peaks characteristic of polysaccharides. The polysaccharide prepared by ultrasonic extraction (U) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 8.60 : 80.90 : 7.41 : 2.68 : 0.57. The polysaccharide obtained by hot water extraction (H) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 9.36 : 79.72 : 8.18 : 2.60 : 0.42. The polysaccharide obtained by ultrasonic-assisted hot water extraction (U + H) was composed of mannose, glucose, galactose, xylose and fucose in a molar ratio of 6.75 : 82.66 : 7.14 : 2.30 : 1.12. The molecular mass distribution of U consisted of 13152 (83.61%), 281 (3.02%), and 53 kDa (13.37%). The molecular mass distribution of H consisted of 10232 (93.15%), 281 (1.94%) and 61 kDa (4.90%). The molecular mass distribution of U + H consisted of 10471 (98.59%), and 60 kDa (1.40%). The results of cell counting kit-8 (CCK-8) showed that the polysaccharide extracted by ultrasonic extraction at low concentrations of 5 and 10 μg/mL had a slightly toxic effect due to the degradation of large molecular mass polysaccharide fractions, while the other concentrations of U and all concentrations of H and U + H had no significant toxicity to macrophages. Neutral red test results showed that the three polysaccharides could enhance the phagocytic activity of macrophages significantly but differently (P < 0.05). The phagocytic rate of macrophages treated with U was 193.45% compared to 163.64% and 187.62% with H and U + H, respectively. This study provides a theoretical foundation for the directional preparation of P. eryngii polysaccharides with specific functional activities.