Preparation And Properties Of Starch-crosslinked-cyclodextrin Porous Absorbent

As a non-toxic and economical adsorbent,porous starch has been used as drug carrier,pollutant adsorbent and encapsulant for dietary supplements due to its high porosity,high specific surface area,strong adsorption capacity,and large loading capacity adsorption capacity characteristics.However,its high porosity structure leads to poor particle strength and stability and the strong hydrophilicity of starch also seriously restricts the loading of hydrophobic components.In this study,?-cyclodextrin(?-CD),with good adsorption performance and rigid molecular structure,was introduced into starch structure by chemical crosslinking method,and a new porous crosslinked starch was successfully prepared by enzymatic hydrolysis technology.Excellent thermal stability,shearing resistance and adsorption capacity on hydrophobic active ingredients were achieved by the modified starch,which provides a reference for developing porous starch materials and expanding its application range.Firstly,the effect of the crosslinking between ?-CD and corn starch(CS)on the adsorption properties of porous starch were investigated.Cyclodextrin crosslinked starch(CS-CD)was prepared via chemically crosslinked method with ?-cyclodextrin(?-CD)and corn starch(CS)as raw materials as well as epichlorohydrin(ECH)as crosslinking agent.Afterwards,the porous cyclodextrin crosslinked starch(PCS-CD)was obtained by the enzymatic hydrolysis.It was found that when the crosslinking reaction was carried out under 50? for 6 h at a material ratio of 20:0.8(w/w),reaction p H of 10 and the enzyme addition of the subsequent enzymatic hydrolysis at 0.5%,the best oil absorption capacity can reach up to 316.28% and good pore formation and uniform pores distribution can be achieved.Secondly,the structure characterization and physicochemical properties analysis of CSCD were carried out by fourier infrared spectroscopy(FT-IR),X-ray diffraction(XRD),scanning electron microscopy(SEM)and differential scanning calorimetry(DSC).The result of FT-IR demonstrated that CS and ?-CD were successfully crosslinked through ether bonds.The results of XRD,SEM and DSC showed that the crosslinking reaction would maintain the starch granular structures,but decrease the relative crystallinity and thus increase the heterogeneity of starch.Compared with the CS,higher pasting temperature(increased from 79?to 85.60?),better thermal stability,better swelling resistance,and better shearing resistance of CS-CD were observed by the analysis of rapid viscosity analyzer(RVA),water solubility index(WSI),swelling index(SPI)and paste clarity.Meanwhile,the introduction of ?-CD significantly improved the enzyme susceptibility of CS-CD.Thirdly,the effect of enzymatic modification on the structures and physicochemical properties of CS-CD were investigated.The results of XRD and DSC analysis showed that the amorphous regions and the weak hydrogen bonds among molecular chains of CS-CD were destroyed by enzymatic hydrolysis,thus the crystal region was improved markedly.The analysis results of RVA,WSI,SPI and paste clarity showed that the enzymatic hydrolysis reaction retains the characteristics of CS-CD,and has good swelling resistance,thermal stability and shearing resistance.Finally,curcumin,as a hydrophobic active substance adsorption model,was systematically explored the effects of the addition amount of PCS-CD,adsorption times,adsorption temperatures and initial concentrations of curcumin on the adsorption capacity.The maximum adsorption capacity was achieved by 60.06 mg/g which was 6 times higher than that of porous starch-based adsorbents reported.Moreover,adsorption kinetics model,thermodynamics model and isotherm model were used to fit the adsorption process of curcumin.And the fitting results of showed that the adsorption of curcumin by PCS-CD corresponded the pseudo-first-order kinetic model.And Langmuir adsorption isotherm was observed under the temperature of 303 K and 323 K,while Freundlich adsorption isotherm was observed under 343 K.Furthermore,it was confirmed that PCS-CD and curcumin was bound by physical adsorption under hydrogen bond and hydrophobic force,as well as a spontaneous adsorption process.In addition,the stability analysis showed the thermal stability and p H stability of curcumin were improved by the adsorption and load of PCS-CD.