Ultrasonic extraction, structural modification and gastric mucosal cells protective activity of a polysaccharide from Dendrobium denneanum

Optimize the ultrasonic extraction process of polysaccharides from Dendrobium denneanum by Response surface design (RSM). The main polysaccharide (DP40) from was separated by anion exchange chromatography, and its structure was modified by low-temperature plasma. The results showed that the polysaccharide extraction rate of ultrasonic was 22.98 ± 0.97%, which was significantly higher than water extraction method(P < 0.05). FT-IR showed that low-temperature plasma modification could improve the water solubility and OH content. NMR showed that the 1 → 6 glycosidic bonds of DP40 are transformed into 1 → 4 glycosidic bonds and 1 → 3 glycosidic bonds, and the α-configuration sugar ring is transformed into β-configuration after plasma treatment. SEM and TEM analysis showed that the morphology of modified DP40 changed from layered porous network structure to smooth morphology, and bulged into semicircular particles, and the degree of cross-linking of surface molecules increased. The results of biological activity experiments indicated that the modified polysaccharide (500–1000 μg·mL−1) can significantly improve the survival rate of GES-1 cells (p < 0.01). Compared with the untreated group, the high concentration of 1000 μg·mL−1 DP40-plasma could not only reduce ROS by 14.5% (p < 0.05) and MDA by 27.45% (p < 0.05), increase SOD activity by 28.27%, but also reduce cytokines (IL-8, TNF-α, IL-1β) by 31.82% (p < 0.05), 33.23% (p < 0.05) and 21.97% (p < 0.05), respectively. At the same time, low-temperature plasma modification can effectively reduce the caspase 3 activity, prevent cell apoptosis, and protect gastric mucosal cells from ethanol damage. Therefore, low-temperature plasma modification can improve the biological activity of DP40 polysaccharide by altering its structural characteristics. The results provide a new idea for the application of low-temperature plasma modification in biomacromolecules.