Effects of Different Chemical Modifications on the Polysaccharide Structure, Antioxidant, and Whitening Activities of Lavandula angustifolia Mill

This study aims to systematically evaluate the effects of chemical modifications on the physicochemical properties, antioxidant activity, and whitening activity of LAP. Four polysaccharide derivatives were prepared through carboxymethylation (LAP-C), selenylation (LAP-Se), sulfation (LAP-S), and phosphorylation (LAP-P) modifications. The results indicate that LAP and its derivatives are all heteropolysaccharides composed of fucose, rhamnose, and mannose. Compared with the original polysaccharides, the chemically modified polysaccharides exhibited significant differences in viscosity, solubility, molecular weight (Mw), microstructure, crystalline characteristics, and thermodynamic properties. Antioxidant activity experiments revealed that different modification methods had varying effects on the biological activity of the polysaccharides. However, all derivatives effectively inhibited H₂O₂-induced oxidative stress by regulating malondialdehyde (MDA) content and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Whitening activity experiments demonstrated that all derivatives were more effective than the native polysaccharide in reducing melanin content and tyrosinase activity. Among them, LAP-S exhibited the strongest inhibitory effect, reducing melanin content and tyrosinase activity by 56.49% ± 0.37% and 67.45% ± 0.32%, respectively, compared to the model group. In contrast, LAP-Se showed the weakest inhibitory effect, with melanin content and tyrosinase activity decreasing by only 37.77% ± 0.29% and 50.87% ± 0.35%, respectively, compared to the model group. This study indicates that LAP and its derivatives hold significant potential for application in the development of novel skincare products.