Reactive extrusion: A review of the physicochemical changes in food systems

In recent years, the functionalization of food-based materials has generated considerable interest as a new route to develop clean label ingredients intended to replace chemically extracted or synthesized counterparts. Extrusion processing offers unique opportunities for functionalizing food ingredients for commercial utility. Extruders can function as a continuously operating bioreactor with options to vary several configurational and operational variables. Many complex structural and chemical changes are known to occur in the form of hydrolysis (dextrinization), molecular interactions (hydrophobic and disulfide interactions, conjugation), and conformational changes in an extruder. However, understanding of the process variables (temperature, shear, residence time, moisture, feed rate etc.) and their composite effects on the conformational and biochemical changes induced in the feedstock is required to fully exploit the opportunities offered by extrusion for functionalization of food materials. This review focuses on the chemical and conformational changes that can be directed in an extruder to produce extrudates of desired attributes. It also reviews the recent advances made in extrusion technology for the targeted functionalization of selected food materials.