| Micro-porous starch is a kind of natural, economical and easily accessible material. On account of its large BET surface area, voluminous micro-pores and excellent adsorption capability, micro-porous starch has been widely applied in the field of food, pharmaceuticals, cosmetics, pulp and paper industries, as well as agriculture. The manufacturing methods of micro-porous starch include enzymatic hydrolysis at temperatures below the starch gelatinization temperature, foaming at high temperature and exchanging solvent.In this dissertation, starches of cassava, sweet potato, corn, peas, wheat and potato were employed as experimental materials, the process route, optimum parameters. micro structure, hydrophilic and lipophilic adsorption property of micro-porous starch and cross-linked starch were investigated. The technological route and optimum parameters of a new technology of processing wheat micro-porous, gelatinization starch by exchanging frozen solvent, were also investigated. The method of processing superfine zinc oxide with micro-porous starch as raw material was explored, and optimum parameters were studied.1. Corn micro-porous starch was prepared by the method of enzymatic hydrolysis at temperatures below the starch gelatinization temperature. Results indicated that the optimum conditions were starch concentration (V/V)15%, enzyme amount4%, glucoamylase-amylase ratio4:1, buffer pH4.4, reaction time12h and temperature50℃.By comparison physical and chemical characteristics of micro-porous starch with that of original one, the size and volume of aperture, specific surface area and adsorption capacity of micro-porous starches were greatly improved. The surface of micro-porous maize starch granule was riddled with holes, forming a hollow microstructure after enzymatic hydrolysis. The water-absorption capacity of porous starch amounted to143.01%, increasing by134.15%than original starch.2. The adsorption thermodynamics and kinetics of the micro-porous starch was studied, and result showed that the adsorption mode of methylene blue by micro-porous starch corresponded well with quasi two level dynamic equation. This adsorption fitted into Freundlich isothermal adsorption equation. When system temperature increased, the amount of adsorbed methylene blue decreased gradually. So it could be inferred that the adsorption process was an exothermic and spontaneous one, with thermodynamic parameters as:ΔGθ<0, ΔHθ<0, ΔSθ<0.3. The adsorption capacity of six types of starches was compared; the sequence was corn starch, tapioca starch, sweet potato starch, pea starch by descending order. Almost no aperture could form after potato and wheat starch were treated by enzymatic hydrolysis.Since wheat starch was difficult to be hydrolyzed by enzymes and form porous structure in starch granules, we added physical pretreatment before enzymatic hydrolysis. The pretreatment methods included ultra-high pressure, ultraviolet irradiation, ultrasonic treatment, annealing, cold solvent exchange processing. Results showed that these treatments had different effect on starch granules, but still could not form pores after enzymatic hydrolysis. The micro-porous wheat starch could be processed by gelatinizing, freezing starch, and exchanging solvent.The optimum process was adding5g starch into40～50mL water, keeping the mixture in a water bath at90℃for25～30min to gelatinize starch, cooling down it to room temperature, storing it in a refrigerator at5℃for48h, cutting it into cubes, freezing it at-10℃for48h, rinsing it with ethanol-water (ratio10:0) for3times, drying it, and the pores forming on the surface of wheat starch granules. So obtained micro-porous wheat starch granules had the merit of uniform pore size, which is desirable for multiple-purpose porous materials. Compared with the original starch, the water-absorbing capacity of porous starch approached to245.66%, increasing by300.20%.4. In order to improve the adsorption capacity of micro-porous starch, the hydrophilic and lipophilic adsorption was modified, its shear resistance capability and heat stability was improved, and a process of cross-linking and enzymatic hydrolyzing to make micro pores was employed to treat starch. Results indicated that the optimal preparation parameters were starch concentration (V/V)15%, epichlorohydrin dosage0.04mL/100g, enzyme amount5.0%, glucoamylase-amylase ratio4:1, buffer pH4.4, reaction time12h, temperature50℃. A systematic comparison of the physical and chemical characteristics was made between crosslinked micro-porous starch granule and microporous starch granule. The crosslinked micro-porous starch had larger pore size (2.4μm diameter) than that of micro-porous starch (1.7μm diameter), larger micro-pore volume, greater water-absorption capacity (150.97%) than that of micro-porous starch (143.01%), greater oil-absorption capacity (1.5mL·g-1) than that of micro-porous starch (1.4mL·g-1), so the absorption capacity was greatly improved. The hydrophilic and lipophilic adsorption, resistance to shear action, heat and cold stability, structure of micro pores were also improved.5. On account of their excellent adsorption capacity, the micro-porous starch and cross-linked porous corn starch could be applied to the preparation of fine chemical products. The paper used wheat starch with micro pores as a template in the preparation of ultrafine zinc oxide. The superfine zinc oxide was successfully processed by a calcination technique carried out in liquid phase, coupled with a powder process. |
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