Because of the rapidly growing interest we have added chapters on transgenic crops as well as a chapter on beer and wine production. As with the third edition we have refined and expanded the material in all chapters. The basic principles of food chemistry remain the same, but much additional research carried out in recent years has expanded and in some cases refined our knowledge. The original concept for the preparation of this book was to present basic information on the composition of foods and the chemical and physical characteristics they undergo during processing, storage, and handling. This book was designed to serve as an introductory text for courses in food chemistry as part of food science programs meeting the Institute of Food Technologists standards. The tripartite (analytical, thermodynamical and structural) approach to water in foods will be examined based on examples of sugars and sugar rich products. A further step in unveiling the behaviour of water in foods consists in determining water molecules in the molecules in the studied food matrix. Such a parameter a w should hold an important place in the identi®cation of the food product, especially as regards its shelf life. This has to be completed with the measurement of the thermodynamic activity of water in the food. Studying water in foods should start with an anlytical determination of water content for commercial and legal reasons which are evident. Of particular importance are the interactions (hydrophilic, hydrophobic) between water and the components of the foodstu and the eect of the soluble molecules of the food on the hydrogen bonding in solvent water. The understanding of why certain products are more stable than others at the same a w needs an elucidation of water structure. Water activity a w brings a supplement of information as it accounts for the availability of water for degradation reactions. Determination of water content, whatever the accuracy of the analytical method, is not suciently informative in relation to the stability of the investigated food product.
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