Water-Holding Capacity of Proteins with Special Regard to Milk Proteins and Methodological Aspects—A Review

During recent years much attention has been paid to the great variety of functional properties of milk proteins. The food manufacturing industry has come to realize that milk proteins have a great potency for contributing various properties for improving a variety of food products. This potential has been the subject of many studies [for comprehensive reviews, see (22, 30, 31, 62, 65, 67,89,92,93, 94, 95, 99)]. Among these properties, waterholding capacity is increasingly regarded as an important factor. Synonyms used in the literature include water hydration capacity, water absorption, water-imbibing, and water-binding. Although different defmitions of some of these tenns were given in the literature (111), all have been aimed at describing the amount of water that can be bound or retained by a protein matrix under defmed conditions. The fonns of water in foods were classified generally in a three class system including bulk or free water, water held by adsorption in multilayers, hydrodynamic hydration, and structural water, but at present there is no unifonn set of defmitions to describe these states (48). In this context, Mohsenin (90) summarized vividly the correlation between the moisture content of foods and the behavior of water as free and bound water. Other authors (36) used different parameters to describe the types of protein and water interactions such as chemisorption, ice-structured water, imbibation, and stearic exclusion. A particular defmition for overall water-holding capacity as a physical property was given for the first time by Hennansson (52), who defmed it as the ability of a food structure to prevent water from being released from the three-dimensional structure. Because several reactions are contributing to this property, this definition implies that a clear understanding of the waterholding ability of a substance can only be 2027