Dear Colleagues,

Freeze-drying is a process that combines the advantages of the two basic methods of food preservation: freezing and drying. Freezing of the material allows to inhibit the biological, enzymatic and chemical processes. Drying process reduces the water activity and water content to the level that obtained product has a long shelf life. As a result, the lyophilised products maintain a nutritional value similar to a fresh material. The removal of water from a frozen state enables to obtain the porous structure, making the rehydration of product quick and effective. The freeze-dried product is an example of very attractive food with high quality that can last for months or years. However, to able to meet it the several conditions have to fulfilled: the process parameters must be selected in such a way as to prevent the thawing of product as well as to maintain the nutritional value of the raw material and the product must be properly packaged and stored, the process must be carried out taking into account the optimization of energy consumptions. An additional difficulty is the fact that the selected process parameters must take into account the chemical composition and structure of the product. The understanding of the process of freeze-drying sets out a broad field of research. Collecting in a special issue the results of research concerning the kinetics of the freeze drying  process, the use of appropriate pre-treatment before drying for a specific raw material, the evaluation of changes in chemical composition and physical properties after freeze-drying of foods and during storage, the assessment of probiotic food activity, the methods of process optimization will make a significant contribution to the development of knowledge about freeze-drying. It will have also a practical aspect because this elaboration can be used by food producers.

Dr. Dorota Nowak
Dr. Ewa J Jakubczyk
Guest Editors

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• freeze-drying
• nutrition value
• structure
• texture
• rehydration
• enzyme activity
• sorption properties
• pre-treatment methods
• glass transition
• physical properties