Generation of Product Structures During Drying of Food Products

Abstract

The sensorial profile, nutritional quality, and rehydration properties of dried food depend on the structure of the dehydrated material. The molecular, supramolecular, micro-, and macrostructure is influenced by the applied drying conditions. During drying of foods, specific product structures can be generated. For instance, during drying at elevated temperatures, Maillard reactions are accelerated. Thus, peptides and reducing sugar molecules are transformed into taste-active molecules. During drying, proteins are also denatured, and their three-dimensional structure changes accordingly. Following this denaturing, proteins can coagulate. Furthermore, gelling of starch is observed during drying of food. In addition to these reactions, isomerization, oxidation, and various other reactions are accelerated during drying at higher temperatures. Thus, the molecular structure of food products changes significantly during most drying processes. Depending on the drying conditions, different supramolecular structures of solid food products are generated during dehydration of solutions. The drying velocity has a significant impact on the characteristics of the generated supramolecular structure. Fast dehydration of liquid products leads to amorphous structures, whereas slow drying allows substances with low molecular weight to crystallize. Furthermore, the chosen drying technology, solid content of the wet product, composition, pressure fluctuations during drying, and the kinetics of mass transfer influence the generation of microstructures. In addition, the liquids can be enriched with gas before drying in order to increase the product's porosity. Finally, the macrostructure and the optical appearance of the dry product are affected by the drying technology applied and the chosen drying conditions.

Keywords:

• Drying
• Food
• Microstructure
• Molecular structure
• Supramolecular structure

Notes

This article was a Keynote Lecture at the 17th International Drying Symposium (IDS2010), held October 3–6, 2010, in Magdeburg, Germany. Other articles from IDS2010 were published in special issues of Drying Technology, 29(13) and 29(16).