The structure and interactions of starch with food constituents.

For most starch-containing foods, the physical and functional properties can be traced to characteristic molecular species being present, their interactions with each other, and modifications caused by environmental conditions (moisture, temperature, shear) during processing and storage. In the present paper, the chemistry and physical chemistry of starch are discussed with an emphasis on how structure (molecular and supermolecular) and composition influence the functionality of this polysaccharide. New experimental findings brought forward on structure indicate that this polymeric carbohydrate is found in various metastable states, depending on the thermomechanical history of the product. Even more important to processing and quality attributes of starch products is the recognition that the dynamics of the supermolecular structure and interactions between starch and other food constituents are governed by the mobility of the amorphous phase of each particular system. In this respect, water, acting as a plasticizer, depresses the glass transition temperature (Tg) and thereby alters the kinetics of state transformations (e.g., gelatinization, retrogradation) and reactivity of starch. The effects of water on phase transition behavior of starch as well as the underlying molecular mechanisms to the phenomena of gelatinization, gelation, retrogradation, and starch-lipid interactions are reviewed herein. Finally, consideration is given to factors affecting the digestibility of starch from the viewpoint of processing-related changes in the susceptibility of starch to alpha-amylase.