Effect of different extraction methods on the structure and anti-aging skin activity of Ulva pertusa Kjellm polysaccharide

This study aimed to investigate the differences in structure and activity of polysaccharides from Ulva pertusa Kjellm extracted by different methods, including hot water extraction (HWE)-HUP, microwave-assisted extraction (MAE)-MUP and ultrasonic-assisted extraction (UAE)-UUP. The polysaccharide extraction rates for HWE, MAE, and UAE all exceeded 20 %. Compared to HUP, MUP and UUP exhibited superior chemical profiles, but had no significant effect on molecular weight (p$>$0.05). FT-IR and NMR analysis confirmed that the functional group composition and main chemical bond types of three polysaccharides remained consistent. SEM and XRD images showed that the morphological structure of MUP and UUP were more porous, but they were still amorphous structure presented by polysaccharides. The antioxidant and anti-aging skin properties of Ulva polysaccharides were evaluated by multiple assays, including DPPH•, •OH and ABTS⁺ radical scavenging rates, SOD, MDA, β-GAL and Col-I content, and Sirt-1 and MMP-9 expression. At 200 μg/mL, the anti-aging akin activity of three polysaccharides all showed twice the improvement compared to the model group. Among the three extracts, UUP with highest sulfated group and uronic acid content presented the best activity. These findings suggest that ultrasonic-assisted extraction holds greater potential for cosmetic applications.