ABSTRACT

Low-temperature vacuum dehydration could avoid heat injury because of high drying temperature, as well as prevent mechanical damage due to ice crystal during freezing. However, it is not clear for the effect of different temperatures and vacuum degrees on the dehydration process. The object of this work was to investigate the drying behavior of broad bean seed and to analyze the effect of moisture diffusion on the structure during low-temperature vacuum drying process. For this purpose, a test bench for low-temperature vacuum dehydration was designed and established. The nine dehydration operating conditions at temperatures of 0°C, 4°C, and 8°C and vacuum degrees of 95, 97, and 99 kPa were conducted. The key parameters including dehydration time, dehydration rate, shrinkage, effective moisture diffusivity were analyzed. Results showed that by increasing temperature and vacuum degree, the dehydration time obviously shortened, and the dehydration rate was significantly increased. The vacuum degree has an obvious influence on product shrinkage, especially in the thickness of broad bean seed. The average effective moisture diffusivity varied from 0.65 to 2.97 × 10⁻¹⁰ m² s⁻¹ under the tested drying conditions. And the high temperature and low vacuum degree were a better way for reducing the shrinkage of broad bean seed. To avoid structure collapse and cell rupture, the end moisture content of broad bean seed should be higher to 0.05 ~ 0.11.

摘要

低温真空脱水可避免由于干燥温度高而造成的热伤害，并防止冷冻过程中冰晶对机械的损坏。然而，不清楚不同温度和真空度对脱水过程的影响。这项工作的目的是研究蚕豆种子的干燥行为，并分析低温真空干燥过程中水分扩散对结构的影响。为此，设计并建立了低温真空脱水试验台。在0℃，4℃和8℃的温度下以及在95、97和99kPa的真空度下进行了九个脱水操作条件。分析了脱水时间，脱水速率，收缩率，有效水分扩散率等关键参数。结果表明，通过提高温度和真空度，脱水时间明显缩短，脱水速率明显提高。真空度对产品收缩率有明显影响，尤其是蚕豆种子的厚度。平均有效水分扩散率在0.65至2.97×10之间变化^-10 m ² s ^-1在测试的干燥条件下。高温低真空度是减少蚕豆种子萎缩的较好方法。为避免结构崩溃和细胞破裂，蚕豆种子的最终水分含量应高至0.05〜0.11。