Studies On Extraction, Isolation, Physicochemical Properties And Biological Activities Of Polysaccharides From Pueraria Lobata (Wild) Ohwi

Pueraria Lobata(willd.) Ohwi(P. lobata roots), as an edible and medicinal plant, is a perennial deciduous vine root. It shows high nutritional and medicinal values, and polysaccharide is one of its main active components. At present, the development and utilization of the P. lobata roots is mainly focused on the extraction of starch and the flavonoids, but the study on the active polysaccharides consisted in the P. lobata roots is scarce, which limits the depth development and application of the P. lobata roots. Therefore, in the present study, the extraction kinetics of polysaccharides from P. lobata roots were studied by water extraction and ultrasonic assisted extraction, respectively. Different polysaccharide fractions were obtained by ion exchange column chromatography, and their physicochemical properties, molecular characteristics and antioxidant activities were analyzed and compared. The acitve polysaccharide fraction was further purified and its preliminary structure was elucidated. The results obtained are as follows:Hot water extraction and ultrasonic assisted extraction were used to extract polysaccharides from P. lobata roots, respectively, and the kinetic models of them were established on the basis of the second law of Fick diffusion. The obtained results showed that the established models can well reflect the relationship between the radius(R) of the particle, extraction time(t), extraction temperature(T), ultrasonic power(P) and the concentration of polysaccharide in the process of extraction. At the same time, the dynamic parameters, such as the extraction rate(K), effective diffusion coefficient, activation energy(Ea) and half life(t1/2) were calculated according to the models.Three partially purified polysaccharides, which named PS-D1(distilled water), PS-D2(0.1 M Na Cl) and PS-D3(0.2 M Na Cl) were isolated from P. lobata roots by using DEAE-52 Cellulose anion exchange column chromatography. The results of basic chemical composition demonstrated that they were mainly composed of fructose and glucose, and sugar contents were more than 85%, and the uronic acids were consisted in PS-D2 and PS-D3. They had different molecular weights and molecular weight distributions. Congo red test revealed that they did not exist as triple helical structures, but showed random coils or aggregates in aqueous solution. The surface morphologies of them were observed by using scanning electron microscopy(SEM), and the resluts displayed that PS-D1 and PS-D2 presented fibrous dendritic structures, but PS-D3 showed rough surface-like clouds or flake-like morphology.Based on antioxidant activity in vitro and scavenging capacity on free radicals, the obtained resluts showed that PS-D1, PS-D2 and PS-D3 could well scavenge DPPH(IC50 value 3.14、2.85 and 2.31 mg/m L), ?OH(IC50 value 1.56、1.03 and 0.99 mg/m L) and O2-? radicals(IC50 value 2.45、1.94 and 1.46 mg/m L) in dose-dependent manners, and had greater Fe3+ reducing ability(FRAP)(45.01、45.80 and 53.87 μmol Fe2+/g) and Trolox equivalent antioxidant capacity(TEAC)(41.23、44.97 and 53.83 μmol Trolox/g sample). PS-D2 and PS-D3 showed stronger antioxidant activities in vitro than that of PS-D1’s. Meanwhile, anti-glycation effect in vitro assays showed that both PS-D2 and PS-D3 exhibited significant inhibition effetcs on advanced glycation end products(AGEs) during the Maillard reaction.PS-D2 was further subjected to Sephacrayl S-400 gel permeation column chromatography to yield a purified polysaccharide, PS-D2 S. The results demonstrated that the sugar content and uronic acid content of PS-D2 S were 98.1% and 1.3%, respectively, with a Mw of 147.2 k Da. PS-D2 S was mainly composed of glucose and galactose in the molar ratio of 82:1. The backbone structure of PS-D2 S was mainly composed of �' 4)- alpha-D-Glcp(1 �' and �' 2)- alpha-D-Galp(1 �' sugar residues, O-6 branch point in �' 2)- alpha-D-Galp(1 �' sugar residues, which was composed of 1- alpha-D-Glc Up. Thus, PS-D2 S isolated and purified from P. lobata roots was a novel water-soluble acidic heteropolysaccharide, and this was not found in previous reports.