Study On The Cellulase-assisted Extraction Of Astragalus Polysaccharides

Astragalus polysaccharides （APS） is an important active ingredient ofastragalus, which has a variety of functions such as anti-tumor, enhancing andimproving the body’s immunity. The process and mechanism for cellulase-assistedaqueous extraction （CAE） of APS was investigated in this article, and the resultsprovided theoretical bases for development and utilization of APS.The influences of cellulase on the morphological structure of extractionresidue and the compositions of products were studied by using highperformance liquid chromatographic（HPLC）, scanning electron microscopy（SEM） and X-ray diffraction（XRD）. The results showed that cellulase did not causethe degradation of APS, but damaged the structure of astragalus cell, increased thepermeability of cell walls, reduced the resistance of spread, and increased the masstransfer rate.Dynamic equationln（C_∞/（C_∞-C））=kt+b as deduced from Fick’s second lawbased on cylindrical configuration and inner diffusion control, in which apparent rateconstant k=5.78D/λ²R₀²and apparent diffusion constant D’=D/λ². Experiments werecarried to measure the effects of the cellulase dosage, extraction temperature, particlesize of raw material, liquid-solid ratio and rotational speed on kinetic parameters suchas k, D′and apparent activation energy E_a. The results showed that the calculationaldata accorded well with the experimental data, and errors might occur when it wasapplied to the initial stage of extraction with small particle size. Compared with thatof aqueous extraction （AE）, the equilibrium concentration C_∞and k of CAE had asignificant increase. For example, C_∞and k of CAE increased by7.8%and43.2%atcellulase dosage90U/g and40℃. Increasing cellulase dosage increased k but did notchange C_∞, and k no longer changed when cellulase dosage exceeded a certain extent.It was found that C_∞and k of CAE and AE increased with the decreasing of particlesize. The C_∞of CAE and AE increased with the increasing of temperature. The k ofAE increases with the increase in temperature, but the k of CAE increases first andthen decreases, which reached a maximum value at60℃. The relationship of D′withtemperature and particle size was proved to corresponding withlnD ’=-9.27926.7/T+1.76lnR0for AE, whileln ln D’=10.61421.2/T+1.75lnR₀0.035ln（T-329）²for CAE. Values of D′were found to be in the range of2.75×10^-12～1.829×10^-11m²· s^-1 for CAE and2.17×10^-12～1.646×10^-11m²· s^-1 for AE, respectively. The Eawith CAE was3.923kJ·mol^-1, whichdecreased54.5%compared with AE. The increase of liquid-solid ratio was favorableto extraction, and extraction process of APS was based on inner diffusion controlmechanism when the liquid-solid ratio was not less than20mL/g. The rotational speedhad little effect on the extraction of APS with AE; whereas k and C_∞slightlydecreased with increased rotational speed in CAE. The thermodynamic constants ΔH^θ,ΔS^θ, ΔG^θof the extration process were also examined. The results showed thatextraction of APS was an endothermic and entropy increasing process, and it was alsoa spontaneous process, ΔH^θ, ΔS^θof the CAE were larger than those of the AE. Thisindicated that the absorbed energy of CAE was great. In addition, ΔG^θof the extrationprocess became smaller when adding cellulose; which means cellulase is favorable tothe extraction of APS...