水稻种子干燥热动力学分析及损伤机理研究

发布时间：2018-07-02 20:17

本文选题：水稻种子干燥 + 黏弹特性　；参考：《中国农业大学》2017年博士论文

【摘要】：干燥处理对农作物种子储藏至关重要,干燥过程能够降低种子水分含量,减缓微生物造成的腐败,避免冷冻过程产生的损伤,从而延缓种子老化,提高种子储藏时间。不适当的干燥方式会损害细胞膜结构,导致细胞内酶失活,蛋白质变性,种皮破裂,从而使种子失去活力。我国对粮食干燥研究较多,对种子干燥研究相对较少。研究种子干燥过程热动力学特性及其生理生化变化规律,建立科学合理的干燥技术,对种子干燥行业的发展有着重要的指导意义。论文研究水稻种子在不同温度和水分活度下的平衡含水量,并通过GAB、Halsey、Smith、Oswin、Herderson和修正的Chung-Post模型对水稻种子解吸数据进行拟合,发现GAB模型具有最大相关系数和最小误差,其最适合描述水稻种子的解吸过程。通过热动力学分析,得出最小积分熵来确定水稻种子储藏的最适含水量,并评估了焓-熵补偿理论对水稻种子解吸现象的适用性。研究水稻种子在不同温度下的薄层干燥曲线,结果发现Page模型、Two-term模型以及Midilli模型能够很好描述水稻种子薄层干燥特性,其中Page模型的拟合度最高。将水稻种子视为球体,有限圆柱体和立方体,并在此三个形状下分析干燥过程的有效扩散系数,研究发现有效扩散系数随着温度升高而增加,其规律符合阿伦乌尼斯方程,且在球体形状下获得的扩散系数与实验值最为接近。通过动态力学分析仪(DMA)在压缩模式下研究种子的应力松弛行为和动态黏弹性变化规律。研究发现松弛模量随着温度和水分的增加而降低,使用时间-温度-水分叠加原理可以获得松弛模量主曲线,广义的麦克斯韦模型可以很好地拟合松弛模量主曲线的实验数据(R20.997)。水稻种子的动态黏弹性受温度、含水量和频率的影响,温度和含水量的增加会降低水稻种子的储能模量和损耗模量,而频率的升高会增加水稻种子的储能模量和损耗模量。损耗模量和损耗因子随温度变化具有相似的趋势,即随温度的升高而增加,当达到峰值后开始下降。损耗因子的峰值所对应的温度随着种子含水量的增加而降低。通过在不同干燥条件下对种子进行干燥处理,研究干燥后水稻种子的生理生化变化特性及细胞超微结构变化规律。结果表明,在45℃条件下干燥水稻种子,由于打破了种子休眠期,其种子活力指数最高,随着干燥温度的增加,水稻种子的发芽率降低。水稻外壳颜色不随温度的变化而改变,但稻米表面颜色会随着温度增加而逐渐变黄。随着干燥温度升高,种子导电率逐渐增加。种子淀粉结构和胚细胞结构随着温度升高而严重受损。水稻种子活力与干燥过程中细胞结构的完整性密切相关。研究不同干燥条件下水稻种子的发芽率,分析种子起始含水量、干燥温度和干燥时间对种子发芽率的影响。通过多个模型对种子发芽数据进行拟合,研究表明改进的Giner1和2模型能够很好模拟干燥过程水稻种子的发芽率变化,用于预测水稻种子干燥后的发芽率。通过干燥-缓苏工艺对水稻种子进行干燥,探究高温缓苏干燥是否能够保持种子品质的可能性。研究表明:干燥-缓苏处理可以提高干燥效率,降低干燥时间,同时适当的干燥温度、干燥时间和缓苏时间可以打破种子休眠期,保持种子品质并提高种子发芽速率。
[Abstract]:Drying is very important for the storage of crop seeds. The drying process can reduce the water content of the seeds, slow down the corruption caused by the microorganism, avoid the damage caused by the freezing process, delay the aging of the seeds, and improve the storage time of the seeds. There is more research on grain drying in China and less research on seed drying in China. Research on thermal dynamic characteristics and physiological and biochemical changes in the process of seed drying and establishing a scientific and rational drying technology have important guiding significance for the development of seed drying industry. At different temperature and water activity, the equilibrium water content was measured by GAB, Halsey, Smith, Oswin, Herderson and modified Chung-Post model. The maximum correlation coefficient and minimum error of the GAB model were found. It was the most suitable for describing the process of the desorption of rice seeds. The integral entropy was used to determine the optimum water content in rice seed storage, and the applicability of the enthalpy entropy compensation theory to the phenomenon of rice seed desorption was evaluated. The thin drying curves of rice seeds at different temperatures were studied. The results showed that the Page model, the Two-term model and the Midilli model could well describe the thin layer drying characteristics of rice seeds, of which Page The model has the highest fitting degree. The rice seed is regarded as a sphere, a finite cylinder and a cube, and the effective diffusion coefficient of the drying process is analyzed under the three shapes. It is found that the effective diffusion coefficient increases with the increase of temperature. The law conforms to the Al enennis equation, and the diffusion coefficient and the experimental value obtained under the shape of the sphere are the most. A dynamic mechanical analyzer (DMA) is used to study the stress relaxation behavior and dynamic viscoelastic changes of the seeds under the compression mode. It is found that the relaxation modulus decreases with the increase of temperature and moisture. The principal curve of the relaxation modulus can be obtained by using the principle of time temperature and moisture superposition. The generalized Maxwell model can be good. The dynamic viscoelasticity of rice seed is affected by temperature, water content and frequency, and the increase of temperature and water content will reduce the storage modulus and loss modulus of rice seed, while the increase of frequency will increase the storage modulus and loss modulus of rice seeds, loss modulus and loss factor, R20.997. There is a similar trend with the temperature change, that is, it increases with the increase of temperature, and begins to decrease when it reaches the peak. The temperature corresponding to the peak value of the loss factor decreases with the increase of the water content of the seed. By drying the seeds under different drying conditions, the physiological and biochemical characteristics of the rice seeds after drying and the cells are studied. The results showed that the seed vigor index of dry rice seeds was highest at 45 degrees centigrade. With the increase of drying temperature, the germination rate of rice seeds decreased. The color of rice hull did not change with the temperature, but the color of rice surface would gradually become yellow with the increase of temperature. With the increase of drying temperature, the conductivity of seed gradually increased. The structure of seed starch and the structure of embryo cell were seriously damaged with the increase of temperature. The vigor of the rice seed was closely related to the integrity of the cell structure during the drying process. The germination rate of rice seeds under different drying conditions was studied, the initial water content, drying temperature and drying of the seeds were analyzed. The effect of time on seed germination rate was fitted by multiple models. The study showed that the improved Giner1 and 2 model could well simulate the change of germination rate of rice seeds in the drying process. It was used to predict the germination rate of rice seeds after drying. The study shows that dry and slow sustaining treatment can improve the drying efficiency and reduce the drying time. At the same time, the appropriate drying temperature, drying time and time can break the dormancy period of the seed, keep the seed quality and increase the germination rate of the seeds.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S511

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