Sedmak Ivan, Može Matic, Kambič Gorazd, Golobič Iztok
Laboratory for Thermal Technology (LTT), Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia.
Kambic Laboratory Equipment, 8333 Semič, Slovenia.
Foods. 2023 Sep 11;12(18):3399. doi: 10.3390/foods12183399.
Vacuum freeze-drying as a process for achieving high product quality has attracted increasing attention in the last decade. Particularly in the pharmaceutical field and food processing industries, lyophilization can produce high-quality products compared to samples dried by conventional methods. Despite its benefits, lyophilization is a time-consuming and costly process that requires optimization of a number of process parameters, including shelf temperature, chamber pressure, freezing rate, and process time. This paper reports on the implementation of heat flux measurements that allow noninvasive real-time determination of the endpoint of the primary drying stage as an essential parameter for the effective optimization of the overall drying time. Quantitative analysis of the drying kinetics of five fruits (kiwifruit, avocado, Asian pear, persimmon, and passion fruit) was assessed by comparing the heat flux and temperature profiles of samples during the lyophilization process. For a 24 h lyophilization cycle, average heat fluxes in the primary drying phase ranged from 250 to 570 W/m. A significant correlation was found between the temperature and heat flux distributions at the estimated endpoint of the sublimation process and the corresponding transition into the secondary drying stage. Furthermore, good agreement was also found for the freezing phase. The use of real-time heat flux measurements proved to be a cost-effective experimental method to better understand the process variables in order to reduce the lyophilization cycle time and overall energy consumption.
在过去十年中，真空冷冻干燥作为一种实现高产品质量的工艺受到了越来越多的关注。特别是在制药领域和食品加工业中，与通过传统方法干燥的样品相比，冻干可以生产出高质量的产品。尽管具有诸多优点，但冻干是一个耗时且成本高昂的过程，需要优化许多工艺参数，包括搁板温度、腔室压力、冷冻速率和工艺时间。本文报道了热通量测量的实施情况，该测量能够非侵入式实时确定主干燥阶段的终点，这是有效优化总干燥时间的关键参数。通过比较冻干过程中样品的热通量和温度曲线，对五种水果（猕猴桃、鳄梨、亚洲梨、柿子和百香果）的干燥动力学进行了定量分析。在24小时的冻干周期中，主干燥阶段的平均热通量范围为250至570瓦/平方米。在升华过程估计终点处的温度和热通量分布与相应的向二次干燥阶段的转变之间发现了显著相关性。此外，在冷冻阶段也发现了良好的一致性。事实证明，使用实时热通量测量是一种经济高效的实验方法，有助于更好地理解工艺变量，从而减少冻干周期时间和总体能耗。
