| Antioxidants are substances that delay the oxidation process, thereby helping to slow down the ageing process and prevent cancer, cardiovascular disease, heart disease, diabetes mellitus, malaria, and rheumatoid arthritis, among others. The search for natural and safe antioxidants obtainable from natural sources has gradually aroused people's interest. In this thesis, the preliminary chemical characteristics and antioxidant property of acidic polysaccharides from Sargassum fusiforme and mango peel were investigated, as well as the antioxidant activity of the mango peel's ethanol extract. The details are provided below:1. Sargassum fusiforme (Harv.) Setchel (S. fusiforme) was extracted with hot water and then precipitated by using 95% ethanol. The precipitates were deproteined, decolorized, and dialyzed to afford the crude polysaccharides of S. fusiforme (SFPS). The SFPS were then fractionated and purified through a gel-filtration column of SephacrylTM S-200 to produce three fractions (SFPS-A1, SFPS-A2, and SFPS-A3). The polysaccharides also underwent fractionation and purification through an anion-exchange column of DEAE-Sepharose Fast flow to produce SFPS-B1 and SFPS-B2. Their homogeneity and molecular weight were determined by HPGPC. The uronic acid content was determined using the carbazole-sulfuric acid method, which requires glucuronic acid as the standard. The result shows that each of them were homogeneous and contained large amounts of uronic acid. Furthermore, their chemical characteristics were preliminarily analyzed by GC-MS combined with IR and NMR spectroscopy. All of them, including the SFPS-A1 and SFPS-A2, wereβ-glycosidically linked.2. The antioxidant activity of SFPS and its fractions were evaluated using different assays. The anti-lipid peroxidative activity of crude polysaccharides was analyzed using aβ-carotene bleaching assay, showing that SFPS have a good antioxidative activity. The radical-scavenging activities of these five SFPS fractions were tested using superoxide and hydroxyl radical-scavenging assays. The results show that all of these fractions possess antioxidant activity, and that SFPS-A1 and SFPS-A2 exhibit a stronger superoxide radical-scavenging ability than Vc. Their antioxidant ability probably correlates with sugar composition: the more kinds of sugar the fraction has, the stronger the antioxidant activity it possesses.3. Mango peel was extracted using 95% ethanol, and then partitioned by ethyl acetate to produce ethyl acetate extract (EAE). The antioxidant activity of EAE was studied using radical-scavenging assays, with Vc as the positive control. The results show that the DPPH·radical-scavenging ability of EAE (IC50=4.4μg/ml) was comparable to that of Vc (IC50=4.2μg/ml). In addition, the·O2- radical-scavenging ability of EAE was stronger than that of Vc (EAE: IC50=6.5μg/ml, Vc: IC50=35μg/ml), showing that EAE has a very strong antioxidant activity. HPLC analysis showed that EAE containsβ-carotene; this was further proven by NMR spectrometry.4. The crude polysaccharides (MPPS) from mango peel were found to contain large amounts of uronic acid (60.57%) composed of D-rhamnose, L-arabinose, D-xylose, D-glucose, and D-galactose. Theβ-carotene bleaching assay showed that MPPS has good antioxidant activity.In addition, the research status of natural antioxidant was simply reviewed.
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