Evaluation of the quality and stability of freeze-dried fruits and vegetables pre-treated by pulsed electric fields (PEF)

This study investigates the application of Pulsed Electric Field (PEF) technology to improve the freeze-drying process, the final product quality and the stability of kiwi fruits, red bell peppers, and red beetroots. Freeze-drying is a fundamental drying technology that aims to maintain the natural attributes of food, but it often leads to challenges such as prolonged drying times and quality degradation. To further understand the implications of applying PEF before freeze-drying, the storage stability of the freeze-dried samples was investigated under both illuminated and dark conditions. PEF treatment was carried out at constant electric field strength of E = 1.0 kV/cm, and specific energy input was varied between 0.2 and 20.8 kJ/kg. This study revealed that PEF treatment significantly decreased the freeze-drying time (2-fold) exclusively for bell peppers. PEF treatment substantially improved volume retention and rehydration capacity for both kiwi fruits and bell peppers, indicating enhanced structural integrity. However, applying PEF had an overall adverse impact on the colour stability of the freeze-dried samples (ΔE > 3). The quality decline was mitigated storing the samples in dark conditions. The results of this study suggest that applying PEF before freeze-drying can represent a promising strategy to enhance the quality of freeze-dried products with improved drying kinetics, volume retention, and rehydration capacity. Careful consideration of storage conditions is essential to prevent the deterioration of product quality over time.