| In the present study,native wheat starch,A-type and B-type wheat starch granules are applied to prepare porous wheat starches by repeated heat-moisture treatment combined with compound enzymatic hydrolysis,the structural,physicochemical and adsorption properties of porous wheat starches were investigated.Moreover,the effect of sodium trimetaphosphate(STMP)cross-linking treatment on the structural,physicochemical and adsorption properties of porous wheat starches were explored.In addition,the effect of porous wheat starches and cross-linked porous wheat starches as encapsulants on the encapsulation of curcumin were compared,and the stability of encapsulated curcumin under the conditions of temperature,light and storage time were also analyzed.Firstly,the effect of repeated heat-moisture treatment combined with compound enzymatic hydrolysis on the structural and physicochemical properties of porous wheat starch were investigated.The porous wheat starch prepared by repeated heat-moisture treatment combined with compound enzymatic hydrolysis dual-modification showed lower solubility and swelling power,but a higher gelatinization temperature,specific surface area and total volume compared with porous wheat starch prepared by compound enzymatic hydrolysis.In addition,the dual-modified porous wheat starch exhibited more pores on the surface of the granules,as observed by scanning electron microscopy(SEM).The dual-modified porous wheat starch samples exhibited higher adsorption capacities for water,oil and methylene blue,and the adsorption process could be well described by the Freundlich isotherm model.X-ray diffraction(XRD)and fourier transform-infrared spectroscopy(FT-IR)results showed that all porous starch samples showed similar X-ray diffraction patterns and infrared spectra.Secondly,the effect of STMP cross-linking treatment on the structural and physicochemical and adsorption properties of porous wheat starch were explored.The cross-linked porous wheat starch displayed lower solubility,swelling power and molecular order,but its thermal stability was significantly improved.After the cross-linking treatment,more dense pores were formed on the surface of the porous wheat starch,as observed by SEM.X-ray photoelectron spectroscopy(XPS)results indicated that the phosphate groups bound to the-OH groups on the starch molecules via covalent bonds(C-O-P).Adsorption experiments results showed that cross-linked porous wheat starch had higher adsorption capacities for water,oil and methylene blue compared with the corresponding porous wheat starch.Furthermore,the isotherm data of the cross-linked porous wheat starch fitted to the Langmuir isotherm model compared to the Freundich and Tempkin isotherm models,and the adsorption process was exothermic and favorable.Finally,the effect of porous wheat starches and cross-linked porous wheat starches as encapsulants on the encapsulation of curcumin were compared.All of the porous starch samples encapsulated curcumin with an encapsulation efficiency of70-80%,which was attributed to the higher affinity between curcumin and porous starch samples.FT-IR results indicated that the interaction between curcumin and porous starch occurred through the hydrogen bonding of curcumin with hydroxyl groups.XRD results indicated that once curcumin was encapsulated by porous starch,it would exist in an amorphous state.The stability experiment results showed that the encapsulated curcumin exhibited higher stability under the conditions of different temperatures,light and storage time compared with the free curcumin.The adsorption of curcumin by B-type porous starch granules mainly depended on the surface adsorption,therefore the stability of the curcumin encapsulated in B-type porous starch granules was relatively low.Interestingly,the stability of the curcumin encapsulated in cross-linked porous starch was higher than that of the curcumin encapsulated in uncorss-linked porous starch at 110 ~oC,which was due to the fact that the thermal stability of the cross-linked porous starch was higher than that of the porous starch.These results were consistent with the results of thermal properties analysis and thermal gravimetric analysis.It was considered that repeated heat-moisture treatment combined with compound enzymatic hydrolysis to prepare porous wheat starch by the systematic study on the preparation method of porous wheat starch.On this basis,STMP cross-linking treatment is an effective method for preparing porous starch.The porous starch obtained by the operation process of this method has excellent adsorption propertie,uniform pore diameter,better thermal stability and environmentally friendly,and is expected to be used as an encapsulant in the food industry. |
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