Water is a key element in food structure. Changes in moisture content, thus in structure, are taking place in different food processing operations such as in drying, rehydration, freezing, thawing, cooking or just in the procedure of determining the moisture sorption isotherms. In this discussion, the latter will be used as a convenient example since the procedure is carried out at constant temperature, thus the outcome is free of thermal effects. Moreover, these isotherms are available for a very wide range of food materials and provide important information about the systems water activity. The sorption isotherms, which are relating moisture content to water activity, have only one independent variable. Such isotherms are based on assuming that the same structure is expected for a given moisture content regardless of its history of changes. However, cyclic variations in moisture content are likely to produce structural hysteresis, which in turn produces the same phenomenon in sorption isotherms. Therefore, structure is another variable that should be considered when analyzing sorption isotherms, especially when encountering hysteresis. The mechanisms of such structural hysteresis will be discussed for the different types of food components, those that are sharing water as their solvent, as well as those that can be characterized as a solution of water in a solid matrix. The discussion will also point out the few cases where hysteresis in moisture sorption isotherms of foods may not be the result of structural hysteresis.<br/> <br/> <br/>

Water induced structural hysteresis in food systems

255th National Meeting (2018)

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