| Starch is a complex high-polymer, consisting of loose amorphous regions and interspersed ordered crystalline regions. Water and chemical reagents could not easily enter into the inner crystalline regions because of this unique structure, which results in a high gelatinizing temperature, large viscosity, poor fluidity and poor chemical reactivity of starch. For example, amylase could not react with native starch directly. Therefore, in the traditional fabricating technology of starch sugar, alcohol and lactic acid using starch as the raw material, it is usually necessary to destroy the crystalline structure of starch first. The destroyed structure could be realized by heating the water-absorbed starch, which leads to the expansion and gelatinization of the starch structure. Followed by a hydrolysis process assisted with the catalyst of acid orα-amylase, a kind of dextrin with low viscosity and good fluidity is obtained. Finally the dextrin is saccharified to produce the product. Therefore it is of great interest and significance to explore novel method to promote the hydrolysis efficiency of starch and develop a liquefaction and saccharification processing without steam to reduce energy consumption. In this thesis, cassava and maize starch were first mechanical activated by a high-energy stirring-type ball mill.The main researchful contents as follows:(1) the activated starch with different milling time was used as the starting material. Usingα-amylase as the liquefaction reagent, dextrose equivalent (DE) of the hydrolysis product as an evaluating parameter, the influences of activation time, gelatinization temperature, reaction time, reaction temperature, starch concentration, amylase dosage and PH value on the DE were investigated in detail. It was found that the mechanical activation could obviously enhance the anzymolysis of the starch. That is because the mechanical activation could efficiently destroy the glucoside bond ofα-1,6 glucose and therefore decrease the viscosity, enhance the cold-water solubility and finally improve the liquefaction of the starch. (2) The effects of the combinedα-amylase and saccharification enzymes on the hydrolysis of cassava and maize starch were also studied. The results indicate that the starch hydrolysis degree in the case of double enzymes used is larger than that in the case of one enzyme used. Furthermore, in the case of double enzymes used, the activated starch could react directly with enzyme without gelatinization, which is of great practically significance.(3) High Performance Liquid Chromatography (HPLC) was employed to analyze the product composition of the starch liquefaction hydrolysis. The results show that the contents of reducing sugar (including glucose and maltose) in the gelatinized native cassava starch, activated cassava starch (with activation time of 1.0h) with and without gelatinization are 6.06%, 12.31% and 11.46%, respectively. The contents of reducing sugar in the gelatinized native maize starch, activated maize starch (with activation time of 1.0h) with and without gelatinization are 4.12%, 8.14% and 7.66%, respectively. It can be seen that the reducing sugar content in the activated starch is higher than that in the native starch. In the case of double enzymes used, the hydrolysis product is mainly composed of glucose with a small amount of maltose. The contents of reducing sugar in the gelatinized native cassava starch, activated cassava starch (with activation time of 1.0h) with and without gelatinization are 16.93%, 30.47% and 27.71%, respectively. The contents of reducing sugar in the gelatinized native maize starch, activated maize starch (with activation time of 1.0h) with and without gelatinization are 15.84%, 28.02% and 26.12%, respectively. These results clearly indicate that the mechanical activation processing could really enhance the enzymolysis activity and very good enzymolysis effect could be obtained in the activated starch even without gelatinization. |
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