Noni Fruit Polysaccharide Derivatives: Preparation, Structural Characterization, and Antioxidant Activities Evaluation

Noni fruit polysaccharide has inherent antioxidant activity but suffers from limitations such as insufficient activity and low bioavailability, making chemical modification a feasible strategy to enhance its functional properties. Compared with the existing research on modified polysaccharides, this study uniquely fills the relevant gap: Systematically clarifies the preparation method of chemically modified noni fruit polysaccharide, preliminarily clarifies the intrinsic mechanism of their antioxidant effect, and provides a reliable modification approach for the development of high-value noni fruit polysaccharide products. Three noni fruit polysaccharide derivatives were successfully prepared via chemical modification, and their structural characteristics and antioxidant activities were systematically investigated. In vitro antioxidant capacity was evaluated using ABTS+ radical scavenging, hydroxyl radical scavenging, DPPH radical scavenging, and reducing power assays; in vivo antioxidant activity was assessed based on an ethanol-induced oxidative damage mice model. In addition, the antioxidant mechanism was explored using RAW264.7 cells, and the regulatory effect on related signaling pathways was verified. The key findings of this study showed that all three prepared noni fruit polysaccharide derivatives exhibited excellent antioxidant activity. In the ethanol-induced oxidative damage animal model, the noni fruit polysaccharide derivatives also displayed remarkable in vivo antioxidant performance: They significantly increased the levels of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the organism, while notably reducing the content of malondialdehyde (MDA), a marker of lipid peroxidation, thereby alleviating oxidative damage caused by ethanol. The preliminary mechanism studies further confirmed that the antioxidant activity of noni fruit polysaccharide derivatives was mainly mediated by regulating the Nrf2/HO-1/NQO1 signaling pathway, which is a key pathway involved in cellular antioxidant defense. These results collectively indicated that chemical modification significantly enhanced the antioxidant activity of noni fruit polysaccharide, and the derivatives had stable and effective antioxidant performance both in vitro and in vivo, while also clarifying the specific molecular mechanism underlying their antioxidant effect. This study provides a solid theoretical basis for in-depth exploration of the antioxidant activity and structure-activity relationship of noni fruit polysaccharide and its derivatives, and lays a foundation for their potential application and development in the food and medical fields.