Structural changes of starch subjected to microwave heating: A review from the perspective of dielectric properties

Starch is a vital component of the human diet and is widely used in food manufacturing. Its complex and subtle structure influences its physicochemical properties, thus affecting its application. Microwave heating has experienced increased popularity in the food industry for many diverse uses. Dielectric properties are crucial parameters reflecting the response of food to microwave treatment. Recent studies have often neglected the importance of dielectric properties when investigating the structural changes of starch in a microwave field. This review summarizes the dielectric and microwave absorption properties of starches and starch systems (with water and/or ions). The various possible structural changes of starch under a microwave field are also analyzed, from the macroscopic to the microscopic level (morphology, lamellar structure, crystalline structure and molecular structure), in an attempt to elucidate the essential features of the response of starch to microwave heating in terms of the dielectric properties. Microwaves can directly or indirectly induce a series of changes in the morphology and internal structures of starch granules, closely related to the dielectric properties of the system and microwave input energy. The future research trend will be to regulate and manipulate the structural changes of microwave-treated starch systems from the perspective of changing their dielectric properties and to obtain microwave-treated starch-based food with desirable properties.