The aim of this study was to analyze the impact of pulsed electric field (PEF) pre-treatment of apple tissue on kinetics of freeze-drying preceded by vacuum freezing and physical properties of such processed material. PEF intensified freeze-drying kinetics and thus reduced processing time by 57% in comparison to untreated apples slices. Furthermore, the effective water diffusion coefficient increased by 44% as a result of PEF application. Water activity changes during storage of freeze-dried apple tissue were more evident in the case of untreated material albeit initial water activity was higher in the case of electroporated samples. As proved by thermal properties measurements these differences were linked to higher crystallinity of the PEF treated samples (35.5%) in comparison to the untreated material (11.0%). The freeze-dried fruits subjected to PEF pretreatment absorbed more water than the untreated samples while no changes were observed for hygroscopicity and loss of the soluble solids during rehydration.

Industrial relevance

Obtained results confirm that application of pulsed electric field before freeze-drying makes possible to obtain high quality freeze-dried product preceded by vacuum freezing performed inside freeze-dryer which could reduce freeze-drying time. Since the rehydration capacity of PEF treated material, expressed as ability to absorb water, is better than untreated samples the application of this method could be beneficial when designing instant products. Performed research indicates also that PEF treated freeze-dried apples exhibit better stability expressed by water activity which in turn is related to crystallinity. What more, higher crystallinity of PEF pre-treated freeze-dried samples not only complements the explanation of different physical properties in comparison with intact freeze-dried material but also suggest that sensorial properties may vary.

中文翻译：

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脉冲电场对冷冻干燥苹果组织物理特性的影响

这项研究的目的是分析苹果组织的脉冲电场（PEF）预处理对冷冻干燥的动力学，然后进行真空冷冻和这种加工材料的物理性能的影响。PEF增强了冻干动力学，因此与未处理的苹果片相比，加工时间减少了57％。此外，由于使用了PEF，有效水扩散系数提高了44％。对于未经处理的材料，冷冻干燥的苹果组织在储存过程中的水分活度变化更为明显，尽管在电穿孔样品中初始水分活度较高。通过热性能测量证明，与未处理的材料（11.0％）相比，这些差异与PEF处理的样品（35.5％）的较高结晶度有关。

行业相关性

所得结果证实，在冷冻干燥之前施加脉冲电场使得可以获得高质量的冷冻干燥产品，然后在冷冻干燥机内部进行真空冷冻可以减少冷冻干燥时间。由于用PEF处理的材料的再水化能力（表示为吸收水的能力）比未处理的样品更好，因此在设计速溶产品时，此方法的应用可能是有益的。进行的研究还表明，PEF处理的冻干苹果表现出更好的稳定性，这种稳定性由水分活度表示，而水分活度又与结晶度有关。还有什么，