Study of starch-lipid complexes in model system and real food produced using extrusion-cooking technology

The formation of starch-lipid complexes during extrusion of model system (rice starch added with oleic acid) and real food (rice starch added with pistachio nut flour) was evaluated. Both formulas were extruded at the same processing conditions (temperature profiles, screw speed and water feed content). The formation of starch-lipid complexes in real food, is strongly dependent on water feed content. In fact, at barrel temperature of 128 degrees C, the highest melting enthalpy of real food (6.7 J/g) was obtained only at 21% of water feed content whereas in the model system it was obtained both at 16 and 21%. These results point out the importance to consider all components present in the extruded food in order to study biopolymers modifications that occur during processing. Industrial relevance: Additions of lipids alter the physical and chemical properties of starchy foods. The changes brought about by them in starchy foods have been attributed to the formation of complexes between amylose and lipids. These changes in the functionality of starch are of interest to the food industry and for human nutrition. Lipid complexation with starch is a very important reaction in extrusion cooking that affects structure formation and texture of the extruded products. Most studies on the starch-lipid complex formation during extrusion of model systems like starch and free fatty acids have been carried out, instead very little is known about starch-lipid complex formation during extrusion of flour blends containing fatty meal. This paper points out the importance to consider all components present in the food extruded in order to study biopolymers modifications that occur during processing. For this reason it is very important to use model systems that are not very different to real food and anyhow it would be advisable to verify the obtained results on real food, above all when a relation between macromolecular modifications and quality characteristics of extruded products would be studied. (C) 2011 Elsevier Ltd. All rights reserved.