| Athelia rolfsii exopolysaccharides(AEPS) belongs to scleroglucan and is a kind of extracellular β-glucansecreted secreted by Athelia rolfsii. AEPS which has many excellent features, such as thickening, stability, water holding capacity and anti-tumor activity is favored by a variety of research fields such as food, cosmetics and medicine. But the phenomenon that this polysaccharide has high cost and rely on imports increases the cost of its application. Our research group aimed to reduce production cost of AEPS. AEPS was produced by Athelia rolfsii screened from Clivia and fermented by corn starch and yellow syrup as medium components which was low-cost sources of carbon and nitrogen. The production of AEPS was 16.135g/L. This laid a good theoretical basis for breaking the situation that AEPS was high-cost and depended on imports.But that subsequent studies about AEPS failed to carry out is not conducive to the promotion and application of AEPS. Therefore, in this paper, extraction and purification process of low-cost AEPS was studied, then the moisture- absorption, moisture-retention capacities and viscosity stability of AEPS were analyz- ed, and antioxidant activity of AEPS, in vitro antibacterial activity and heavy metal ion scavenging activity were further studied. These provided a theoretical basis for the production and application of polysaccharide. The main findings are as follows:1. Optimal ethanol precipitation process for AEPS was determined by Box-Behnken design. The optimal conditions of ethanol precipitation for AEPS were determined as follows: 3-fold condensation of the fermentation supernatant before 17 h precipitation at 5 ℃ with an ethanol/fermentation supernatant ratio of 1.7:1(V/V). Under these conditions, the AEPS yield was 12.24 g/L.2. After being decolorizing and dialysed, AEPS was chromatographed by Sephacryl S400-HR. The optimum conditions for chromatography: double distilled water as the mobile phase with 0.5 mL/min flow rate, 4mg sample volume(sample concentration of 1 mg/mL). After being chromatographed, two components AEPS1 and AEPS2 were got. The UV spectrums of AEPS1 and AEPS2 showed that there wasn’t any protein or nucleic acid in polysaccharides and primary structures of AEPS1 and AEPS2 were got through the FTIR spectrums. The number average molecular weight(Mn) and weight average molecular weight(Mw) of AEPS1 were measured by efficient gel permeation chromatography and were 8.06×106 and 1.39×107, respectively.3. The moisture-absorption and moisture-retention capacities of AEPS, chitosan and urea were compared in the environments with saturation(NH4) 2SO4 aqueous(relative humidity 81%) and dry silica gel, respectively. The results showed that the moisture-absorption and moisture-retention capacities of AEPS were superior to those of chitosan and urea. The effects of temperature, p H and ion concentration(Mg2+, Ca2+, Na+, and K+) on the viscosity stability of AEPS were examined. The results showed that AEPS viscosity was very stable in the pH range of 1 to 12 and at ion concentrations ranging from 0 to 1.0 mol/L. But temperature had large effect on viscosity stability. At temperatures in the range of 5–95 ℃, the lowest viscosity of AEPS was 51 mPa·s at 35 ℃. The viscosity of AEPS was increased when the temperature increases or decreases.4. AEPS has antioxidant activity. 4 indicators was used to estimate AEPS antioxidant activity including Fe2+ chelating ability, reducing power and removal abilities of DPPH and ·OH. The results showed that when the concentration of AEPS was 4mg/mL, clearance rate of DPPH and spectrophotometric values for reducing power were 47.98% and 0.303, respectively. When the concentration of AEPS was 1.5mg/mL, clearance rate of hydroxyl radicals(·OH) was 17.6% and kept stable as the concentration of AEPS increasing. When the concentration of AEPS was 2.5 mg/mL, Fe2+ chelating rate was 74.4%.5. Using Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Bacillus subtilis as indicator bacteria, antibacterial activity in vitro of AEPS was studied by inagar hole diffusion method. The results showed that AEPS had no antibacterial activity in vitro for 4 kinds of indicator bacteria.6. Using Cd2+, Cu2+ and Zn2+ in aqueous solutionto as indicator heavy metal ions, the effect of pH, contact time and initial EPS and metal iron concentrations on the metal uptake(qe) was illustrated. The biosorption isotherm was also studied. The results showed that the clearance ability of AEPS for Cd2+, Cu2+ and Zn2+ all reached best at 25℃, pH 5~7 and 60 min reaction time. Compared with Freundlich adsorption isotherm, biosorption datas for Cd2+,Cu2+and Zn2+ all fitted better with the Langmuir adsorption isotherm and according to the qmax value in Langmuir adsorption isotherm, the maximal metal uptakes(qmax) of EPS were 116.28, 103.09 and 153.85mg/g for Cd2+,Cu2+ and Zn2+, respectively. |
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