Effect of Drying Methods on the Structural Characteristics and Antioxidant Stress Potential of Pumpkin Polysaccharides

Polysaccharides (PPs-H, PPs-F, and PPs-I) were extracted from the pumpkin flesh dried by hot air, freezing, and far-infrared drying, respectively. It was found that there were some differences in the color, appearance, and microstructure of the three pumpkin powders. The three PPs had similar infrared spectra and monosaccharide composition, but their microscopic morphology, molar ratio of monosaccharide, molecular weight, Mw/Mn ratio, and configuration of anomeric carbon were different. The scavenging capacities of the three PPs to DPPH·, ABTS+, and ·OH were different, but all of them were concentration-dependent. The three PPs shifted the survival curve of Caenorhabditis elegans to the right under oxidative stress compared with the negative control and significantly reduced the malondialdehyde content by more than 38% (p < 0.05). PPs-F had a leading effect on the mean lifespan, extending it by 28.43%, followed by PPs-H with 23.45%; both significantly upregulated the mRNA expressions on lifespan and oxidative stress-related genes, such as skn-1, sir-2.1, sod-1, sod-2, and sod-3 (>1.21-fold, p < 0.05). In summary, drying methods are chosen according to their effects on structural characteristics and the antioxidant ability of PPs.