Recent Progress and Application of Freeze Dryers for Agricultural Product Drying

Freeze-drying exhibits essential characteristics such as the ability to maintain the original structure, color, and the highest content of nutritional components in fruits and vegetables, and excellent rehydration capability. Combinations of other pretreatment methods with freeze dryers have been employed as efficient, low-cost, and faster dehydration techniques as compared to freeze-drying alone.

Abstract

The impact of various freeze-drying (FD) methods on the drying efficiency and quality of dried fruits and vegetables is reviewed. Additionally, a brief overview of recent advances in FD methods is provided. The FD technique is characterized by the following key properties: ability to maintain original texture and color, the highest nutritional value, and appropriate rehydration rate due to the porous tissue of the product. Recently, various combination methods have been tested to improve the drying speed and save energy when FD fruits and vegetables. This includes combining FD systems with other techniques such as ultrasound, microwave, vacuum, infrared radiation, pulsed electric field (PEF), and CO₂ laser perforation. Combined benefits of these technologies include increased mass transfer rates, shorter dehydration time, energy savings, improved product quality, lower shrinkage, higher rehydration capacity, and flexibility to dry and manufacture the many types of dried fruits and vegetables pieces.

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