【作者】 胡庆国；

【导师】 张慜；

【作者基本信息】 江南大学 ， 食品科学， 2006， 博士

【摘要】 现代干燥技术的发展趋势之一就是多种干燥技术综合应用,使之在干燥的不同阶段发挥不同传热方式的优势,使设备用能更加合理。在本课题中,主要针对以毛豆为代表的颗粒状果蔬的脱水干燥,经多种干燥方式在干燥效率及产品品质等方面的比较,采用前期热风与后期真空微波分段式联合干燥技术,并对其工艺过程进行优化和数学模拟,建立干燥过程的传质模型,达到即满足产品的品质要求,又节能降耗,并最大限度地提高其设备生产能力的目的。首先以毛豆为试验原料,分别采用真空微波、热风、真空冷冻及先热风后真空微波联合等四种不同干燥方式进行干燥,并对产品的Vc和叶绿素保留、收缩与复水性、色泽、质构等力学特性及微观组织结构等多种品质参数的影响进行了对比分析。结果表明:热风与真空微波联合干燥的毛豆干制品不但干燥时间较热风干燥和冷冻干燥大大缩短,在各质量参数上均达到或接近冻干或真空微波干燥的产品水平,但远高于热风干燥的产品。故不论从改善果蔬产品的干燥质量,还是从其经济实用性方面考虑,热风与真空微波联合干燥方法都是一种值得推广应用的干燥方法。针对热风及真空微波两种干燥方式的干燥特点,即:热风干燥前期失水速率较快,而后期非常缓慢;以及真空微波干燥对于后期较难除去的一部分水分干燥效率较高,并且对物料品质影响较小,但在前期存在着因失水速度过快而产生排湿困难,从而会加大了设备的干燥负荷。采用前期热风与后期真空微波的联合干燥方式可从根本上解决这一问题。并对联合干燥工艺参数(转换点时间、热风温度及微波强度)进行了优化,得出最佳工艺参数。分别对毛豆在热风干燥及真空微波干燥条件下的含水量、干燥速率和表面温度的变化进行研究。并采用非线性回归及多元线性回归等数理统计方法对其干燥曲线进行数学模拟,最终建立了热风与真空微波联合干燥的半经验型数学模型。而且与试验结果的拟合度较高。讨论在热风和真空微波干燥下毛豆的有效扩散系数(Deff)和活化能(Ea)变化与其操作条件的关系。采用厚层干燥可进一步提高真空微波干燥设备的生产能力。但根据试验结果表明:在一定操作条件下,干燥速率随着床层物料厚度的增加而增加,水分及温度分布也越不均匀,对产品质量产生的影响也越大。通过采用间歇(缓苏)干燥的方式可改善其水分分布的不均匀性。将热风与真空微波联合干燥与单独热风及真空微波两种干燥过程的能耗进行对比,能耗比单独热风和真空微波干燥过程下降50%左右。更多还原

【Abstract】 The combined application of various drying methods is one of the trends in modern drying technology, which uses the advantages of different drying methods suitable for different phases of a drying process in order to improve power efficiency of the drying equipment. This study compared various drying operations for edamames in terms of drying efficiency and product quality, designed a combination drying process using hot-air in the initial phase and vacuum microwave in the final phase, experimentally optimized and mathematically modelled the whole process, and established the mass transfer model thereof. The optimum drying process thus established provided satisfactory product quality, lower power consumption, and improvements in equipment productivity.The drying effects of vacuum microwave, hot-air, vacuum freezing, and combination hot-air & vacuum microwave drying was evaluated on thin layer with hot-air drying and drying were investigated on edamames in terms of vitamin C and chlorophyll retention, product shrinkage and rehydration properties, color, textural characteristics, and microstructure. Combination hot-air & vacuum microwave drying greatly lessened drying time as compared with hot-air and vacuum freeze drying; and provided similar product quality as compared with freeze and vacuum microwave drying. Combination hot-air & vacuum microwave drying demonstrated significant superiority over hot-air drying to guarantee good product quality. Hence, combination hot-air & vacuum microwave drying deserves promoted application both for economical and product quality considerations.Hot-air drying has advantages of rapid removal the surface water of materials without causing damages to product quality during the initial drying phase, yet disadvantages of extremely low drying rate in the final stage; and vacuum microwave drying has advantages of higher drying rate for removal of residual water in the materials with least damages to products, yet disadvantages of difficulty in oven chamber moisture release in the initial stage, which will increase oven loads. However, combination drying consisted of hot-air drying followed by vacuum microwave drying will fundamentally solve these problems. The drying process parameters were optimized and obtained.The changes in moisture content, drying rate and surface temperature of edamames were examined during hot-air drying and vacuum microwave drying, respectively. Nonlinear regression and multiple linear regression procedures were used to estimate the parameters associated with the drying models, from which a semi-empirical mathematical model was developed for predicting the thin layer drying kinetics of edamames during combination hot-air drying and vacuum microwave drying. This model was proved to be in good agreement with the experimental results under all drying conditions. The moisture diffusivity更多还原