Protein‐water interactions and functional properties

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Abstract
Hydration or rehydration is the first and perhaps most critical step in imparting desired functional properties to proteins in a food system. Water that interacts with the protein molecule exhibits different properties from those of “free” water. The types of water in protein‐food systems are described in terms of structural, monolayers, unfreezable, hydrophobic hydration, imbibition or capillary condensation, and hydrodynamic hydration water. Protein functional properties such as swelling, solubility, gelation, water holding capcity, etc., are directly related to the manner in which the protein interacts with water. Methods for studying the protein‐water interaction are discussed. The primary protein‐water interaction is believed to take place at various water binding sites on the protein molecule. Theories that explain the mechanism of action of these different water binding sites are reviewed. Factors which affect the protein‐water interactions include the number and nature of the binding sites on the protein molecule, protein conformation, plus environmental factors such as pH, salt, temperature and others. Finally, the protein‐water interaction phenomenon and the physico‐chemical and functional properties of proteins in protein isolate systems (dehydrated, solution, and gels) and in protein food systems are briefly examined.