The influence of oil on the properties of slowly-cooled jet-cooked normal corn starch dispersions

Previous work has shown that when aqueous dispersions of normal corn starch are jet-cooked under excess steam conditions, the properties of the final product depend on the manner in which the cooked dispersion is cooled. Phase separation of the component molecules of starch alters the final properties, and the extent of phase separation depends on the cooling conditions. Both irregular, amorphous particles and spherical or toroidal crystalline particles were observed in the cooled products. Stable starch-oil composites with a wide range of applications are formed if oil is jet cooked with starch, and the goal of this work was to examine the effect of the added oil on the rheological and structural properties of cooled dispersions. A Rapid Visco Analyser was used to obtain a range of cooling profiles and stirring rates. The dynamic moduli increased with the addition of oil, and the effect was greater for mineral oil than soybean oil. Light microscopy showed that the crystalline particles were not formed in the presence of oil, but samples with oil contained different types of large and small spherical particles. The change in behavior is attributed to the selective extraction of fatty acid components of native lipid by the oil droplets, or to the preferential accumulation of amylose–lipid helical inclusion complexes at the oil droplet surface.