| In recent years, with the development of agriculture and agricultural products in international trade and business competition intensifies, the issues such as quality and safety of agricultural products,water control,cost planning are becoming more and more important. Maize starch, is the major raw materials of agricultural production, structural changes in processing make its water adsorption capacity different, which influences the adsorption characteristics of products.In this paper, we aimed at the study of the different structures of the starch which is produced in different parameters, the different moisture absorption and desorption characteristics were also evaluated. The samples with different degrees of gelatinization (33.1%, 55.3%, 68.7% and full gelatinization)were made by adjusting processing parameters.(1) Scanning electron microscopy showed that: there is no significant difference between the untreated starch and the starch sample with gelatinization degree of 33.1% in structure, but more complete particle morphology, fewer fragments in the untreated sample. The sample with gelatinization degree of 55.3% ruptures more than the first two samples, but still the majority of particles maintained the original shape. The first three samples of particle shape can still be maintained. The samples with gelatinization degree of 68.7% are obviously not as good as the first three samples, the broken starch fragments are more and the complete small particles are fewer. In the samples with full gelatinization, basically there is no complete particle, starch particles were completely destroyed and the fragments are more, but the adhesion is very serious. In summary, It is relevant between the starch gelatinization degree and the intergrity of the starch, that is, the higher the degree of gelatinization, starch granules, the more damaged the starch particles.(2) X-ray diffraction results show: With the change of intensity of thermal processing, internal microcrystalline structure of starch followed the changes。The sample absorption peak became wider and the gradual absorption curve became flattening, with the heating time increased starch microcrystalline changes from Type A gradual to the amorphous form, due to the crystallization of starch granules being present in the area, so the trend of microcrystalline starch particles extent of the damage with the consistent trend.(3) Using TG-DSC for analyzing the same water content of the samples to monitor water loss changes: With the degree of starch gelatinization increased its remaining water after take part of the total water content is0.45%, 0.38%, 2.96%, 19.76% and 22.35 % respectively after 100℃.(4) Different processing conditions with starch at 25℃and 35℃by the GAB and the BET model to estimate parameters and fitting results assessment, excellent fitting accuracy, respectively R2≥0.988 and R2≥0.994, and the more excellent accuracy gained from BET equation than the result from GAB equation. As the temperature increases the equilibrium moisture content decreased. Analysis showed there is lag between the sorption and desorption, that is, the moisture types of EMC of sorption is lower than the moisture types of EMC of desorption. Using the desorption equilibrium to calculated the moisture content is higher than the value calculated by the sorption. Using GAB model to calculate the value of the single layer water content is higher than the value calculated by the BET. At the same temperature, the same type, with the degree of starch gelatinization increased, the single layer water content decreased which is calculated by GAB and BET model. |
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