Preparation Of Clathrate Maizestarch And Its Structures And Properties

The adsorption capacity of native starch is low. Physical, chemical and enzymatic modifications are effective ways to improve the adsorption capacity. In this research, maize starch was physically modified to produce non-crystalline maize starch (NCMS). NCMS has a flexible unconsolidated molecular chain structure and high activated reactivity. NCMS was used to prepare clathrate maize starch (CMS) through inverse micro-emulsion crosslinking process. CMS is a kind of chemically modified starch with internal micropores and surface pores, small particle size, large specific surface area, large-molecular-adsorbed capacity and sustained-released function. The structures and properties of CMS were investigated thoroughly. The capacities of CMS to adsorb aspirin and ascorbic acid were studied.Maize starch was physically modified by ultrasound, microwave,60Co-γ irradiation, high pressure and ball milling method. Based on the disappeared ratio of polarization cross of starch grains and the mophology of starch granules, the ball milling was selected as the practical modification method to prepare granular NCMS. NCMS was milled using ceramic milling tanks and balls as grinding materials. The optimal processing of NCMS was25%of filling rates,12of the ratio of ceramic grinding balls (Φ20mm Φ10mm),480r/min of milling speed,2.35h of treatment time, and5.71of ball-to-powder mass ratio. The relative crystallinity of NCMS was only1.91%.NCMS granules were prolate, the surface was rough with crack and depression. The particle distribution of NCMS was5～80μm, and its medium diameter was18.87μm. There were2～50nm micropores dispersed in the NCMS. Its specific surface area and pore diameter increased by3and2times of those of native starch, respectively. The birefringence of maize starch granules disappeared completely. X-ray diffraction result showed that NCMS had transformed from polycrystalline structure to an amorphous state. FT-IR spectra showed that there was no appearance of new groups during the modification.13C CP/MAS NMR result showed that the double helices of native starch chains were changed into single helices of NCMS. NCMS had higher values of swelling power, water holding capacity, stability of the paste, and adsorption of methylene blue compared with those of native maize starch. Furthermore, the cold water solubility of NCMS increased by116times. NCMS had lower values of the turbidity, viscosity, gelatinization temperature and thermal enthalpy compared with those of native maize starch.CMS was synthesized from NCMS through inverse micro-emulsion using epichlorohydrin (ECH) and N,N’-methylene bisacrylamide (MBAA) as complex crosslinked agent. The reaction used a mixture of cyclohexane and chloroform as oil phase (Vcyclohexane Vchlorofor=41); Span60and Tween60as an emulsifier (Wspan60WTween60=31); ammonium persulfate and sodium bisulfite as initiator (Wammonium persulfate Wsodium bisulfite=21), and the optimal processing conditions of CMS were: starch milk concentration (130g/L); ratio of oil to water (41); emulsifier dosage (0.28g/L); initiator dosage (0.24g/L); MBAA dosage (0.43g/L), ECH dosage (3.60mL/L). The swelling ratio of CMS was173.94%, and the adsorption capacity of methylene blue was116.23g/kg.CMS had a rough surface and ball or ellipsoidal shape. The surface of CMS had a porous structure, and there was a big cavity in the center of CMS granular. The sizes of starch granule were mainly distributed in the range of0.2～20μm and the medium diameter was9.54μm. The specific surface area of CMS was3.43m2/g, and the average pore size was47.68nm. FT-IR results showed that amide and ether groups crosslinked with starch. The XRD result showed a diffuse diffraction peak indicating that there was no crystal structure generation in the starch granule. CMS had higher values of retrogradation, freeze-thaw stability, thermal properties, peak viscosity, and breakdown viscosity compared with those of NCMS. It also had lower values of solubility, trough viscosity, final viscosity, and setback viscosity compared with those of NCMS. The adsorption capacities of CMS to methylene blue were208times that of native starch and30times that of NCMS. The adsorption capacities to ascorbic acid and aspirin of CMS were137.23g/kg and104.86g/kg, respectively. When ascorbic acid was adsorbed by CMS, it was rapidly released within2h，and continued to release sustainly up to8h in a simulated human body environment. When aspirin was adsorbed by CMS, it rapidly released within2h，and continued to release uniformly from2to6h and sustainly release from6h to12h in a simulated human body environment. Therefore CMS had a surface adsorption capacity and internal embedding capability for ascorbic acid and aspirin.CMS can be widely used as the embedding medium for target food ingredient and a carrier for medicine. It’s adsorption capacity and releasing mechanism for other macro-molecules need further investigation.