| In this work, the waste lignocellulosic materials namely Fructus forsythiae residue (FFR) as raw adsorbent materials, was modified by white-rot fungi for the preparation of a low-cost, safe and effective adsorbent (WMFFR). Physicochemical and structural properties including the specific surface areas, pore volumes, average pore diameters, surface functional groups and microscopic morphologies of FFRand WMFFR were studied comprehensively. Meanwhile, the pontential application of WMFFR in the enrichment of two typical active phenolic compounds (forsythiaside and phillygenin) from F. forsythiae extracts was investigated. The adsorption kinetics, intraparticle diffusion model, equilibrium isotherms and thermodynamic parameters were further researched with the aim to clarify the adsorption mechanisms. Subsequently, a series of dynamic adsorption and desorption tests were performed on WMFFR-packed columns to enrich the target compounds. The main studies and conclusions were as follows:1. Development of the HPLC method for determination of forsythiaside and phillygenin.Detection equipment:Agilent1100HPLC system; Chromatography column:Kinetex PFP100A reversed-phase column (100mm×4.6mm. i.d.,2.6μm); mobile phase:methanol (A)-0.1%formic acid aqueous solution (B); Gradient elution:0-10min20-35%(A),10-20min35%(A),20-25min35-40%(A),25-40min40-65%(A); flow rate:1mL-min-1; column temperature:25℃; injection volume:10μL; detection wavelength:270nm. This method was repeatable, accurate and stable, which was suitable for the determination of forsythiaside and phillygenin in F. forsythiae.2. Optimization of the preparation process of WMFFR. Based on the adsorption and desorption performance of the target compounds on the adsorbent, three key factors including white-rot fungi species, fermentation temperature and fermentation time during the biological modification process were optimized. Optimal conditions were as follows:White-rot fungi specie:Echinodontium taxodii2538Fermentation temperature:28℃Fermentation time:20dayUnder the optimized conditions, the adsorption capacities of forsythiaside and phillygenin on WMFFR were increased by176.23%and189.99%as against those on the un-modified FFR; the desorption capacities of these two target compounds on WMFFR were also increased by188.32%and132.33%correspondingly. Additionally, the adsorption capacities of these two target compounds on WMFFR were comparable to those on D101macroporous resin. However, the desorption ratios of the two target compounds on WMFFR were much higher than those on D101macroporous resin. 3. Comparions of physicochemical and structural properties of WMFFR and FFR. Results showed that the specific surface area (SBET), total pore volume (Vt) and average pore diameter (Dp) of WMFFR were found to be31.32m2·g-1,0.285m3·g-1and26.40nm, respectively. All these values were significantly greater than those of un-modified FFR (8.82m2·g-1,0.018m3·g-1and8.16nm, respectively). Additionally, results of scanning electron microscopy (SEM) showed that the overall structure of WMFFR was looser while having a larger number of pores and cavities as against that of FFR. Moreover, Fourier transform infrared spectroscopy (FT-IR) exhibited that the amount of carbonyl groups existed in WMFFR was enhanced as compared to that of FFR. Furthermore, the particle size of WMFFR was in the range of32.33-33.04μm, demonstrating that it dispersed in aqueous solution homogeneously. In addition, the particle zeta potential of WMFFR was-36.26mV, showing its excellent stability in aqueous solution.4. Application of the WMFFR as a novel adsorbent to enrich forsythiaside and phillygenin from F. forsythiae extracts. The adsorption mechanism of WMFFR for forsythiaside and phillygenin was studied through the adsorption kinetic, adsorption isotherm and adsorption athermodynamic. The adsorption process followed the pseudo-second order kinetic and intraparticle diffusion models. The equilibrium experimental data were well described by both Freundlich and Langmuir isotherms.△G°values for adsorption of forsythiaside and phillygenin on WMFFR at all temperatures were negative,△H°values were-40.50and-36.02kJ·mol-1and△S°values were55.01and46.03J·mol-1·K-1, respectively. Thermodynamic analysis indicated that the adsorption was a physical, spontaneous and exothermic process. At last, the dynamic adsorption and desorption tests were performed systematically on WMFFR-packed columns to obtain optimal operation parameters:Concentration of sample solution:forsythiaside1.648mg·mL-1, phillygenin0.424mg·mL-1pH value of sample solution:4.5Volume of loading sample solution:6BVGradient desorption:10%ethanol solution2BV,60%ethanol solution4BVAdsorption and desorption flow rate:1mL·min-1Under the optimized conditions, the contents of forsythiaside and phillygenin in the initial crude extracts increased from4.12%and1.06%to23.91%and7.44%in the final products with recovery yields of67.41%and81.52%, respectively. Therefore, the result demonstrated that WMFFR could be used as a low-cost, safe and effective adsorbent to enrich forsythiaside and phillygenin from F. forsythiae extracts for their application in both healthcare food and pharmaceuticals. |
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