Optimization of Extraction Process of Polysaccharides from Olea europaea L. Leaves and Its Physicochemical Properties and Antioxidant Activity

In order to increase the development and utilization value of polysaccharides from Olea europaea L. leaves, the extraction process of polysaccharides from Olea europaea L. leaves (OLP) was optimized by orthogonal experiment, the molecular weight was determined by high performance gel permeation chromatography combined with multi-angle laser light scattering (HPGPC-MALLS), and the monosaccharide composition of OLP was analyzed by PMP pre-column derivatization and its antioxidant activity was evaluated. The results showed that the optimal extraction conditions were material-liquid ratio of 1:27.5 g/mL, extraction temperature of 95 ℃ and extraction time of 3.5 h. Under these conditions, the yield of OLP was 2.75%. The average weight molecular weight (Mw) of OLP was 25.36 kDa, the average number molecular weight (Mn) was 19.32 kDa, and the polydispersity was 1.313. OLP was mainly composed of glucose (Glc), galactose (Gal) and galactose amino (GalN), but also contains rhamnose (Rha), arabinose (Ara), xylose (Xyl), mannose (Man) and glucosamine (GlcN), and the relative molar ratio of monosaccharide was 56.2:15.9:10.3:8.3:5.9:2.6:0.5:0.3. The results showed that OLP had good antioxidant activity, with IC₅₀ of 0.422, 0.302 and 0.268 mg/mL for hydroxyl free radical, superoxide anion free radical and DPPH free radical, respectively. The optimum technology of OLP is simple, the yield is high, and the antioxidant activity is good, which provides an essential reference for the further research, development and utilization of OLP.