This study focuses on the behavior of starch and lipids in starchy foods by heat cooking and food processing, and the effects of surfactants on these components. In a study of cooked rice, the density of the external area of cooked rice grains was lower than that of the internal area, indicating greater expansion of external vs. internal areas. The addition of surfactant suppressed the expansion of cooked rice grains. X-ray diffraction and differential scanning calorimetry analysis suggested the existence of amylose-surfactant complexes in the external area of cooked rice grains but not internally. This observation led us to propose the formation of amylose-surfactant complexes in the aqueous layer during cooking. In a model cookie study, scanning electron microscope images showed that the starch granules in model cookies are embedded in lipids. The shape of starch granules was similar among lipid species. The results of gel permeation chromatography analysis suggested that amylopectin in the starch samples of model cookies were largely decomposed during the baking process. Viscosity of the starch samples determined by a rapid visco analyzer was lower than that of wheat starch in all cases. However, the viscosity ranking among lipid species differed from the extent of decomposition among lipid species. These results suggest the existence of another factor affecting the viscosity of starch, such as the ability to form inclusion complexes with lipids. These effects of starch and lipid in starchy foods might participate in product palatability.
