| Sumario: | Some facts concerning the effect of non-equilibrium situations and glass transitions on the water activity (Aw) values of foods in the microbiological growth range are reviewed. Analysis of literature data suggests that although some amorphous intermediate moisture foods are non-equilibrium systems (e.g. very slow rate of attainment of equilibrium), the 'stability' (time dependency) of measured water sorption isotherms, or the prediction of water activity from equilibrium data corresponding to aqueous solutions of main food solutes (NaCl, sugars), are little affected. However, crystallization of amorphous components (sugars), which is also a consequence of non-equilibrium situations, may lead to significant modifications of Aw values in foods. As far as the prediction of microbial growth in foods is concerned, changes in non-equilibrium semi-moist foods may be in many situations slow (within the time frame of the food shelf-life) and/or so small that they do not seriously affect the application of Aw concept as a predictor of microbial growth. However, the use of Aw should always consider the possible influence of some non-equilibrium situations. © 1995.
|
|---|