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United States Department of Agriculture

Agricultural Research Service

Title: Formation of Toroid, Lobed, and Spherical Crystalline Particles During Slowcooling of Jet-Cooked Cornstarch Dispersions

Authors
item Felker, Frederick
item Fanta, George

Submitted to: American Association of Cereal Chemists Meetings
Publication Type: Abstract Only
Publication Acceptance Date: November 9, 2000
Publication Date: N/A

Technical Abstract: Steam jet cooking has been used as a rapid and inexpensive method of solubilizing and dispersing cornstarch for a variety of uses. Co-cooking lipid materials with starch using excess steam forms a starch-lipid composite which, for some applications, is held as a hot liquid awaiting further processing. The purpose of this study was to characterize the formation of crystalline particles in slowly cooled, jet-cooked starch dispersions. Normal dent cornstarch was jet-cooked with 70 psig steam inlet pressure and 40 psig back pressure (140 deg C) to yield dispersions of 4.3% solids. These were held in Dewar flasks for 22 hrs, during which the temperature gradually dropped from 89 deg C to 53 deg C. Crystalline particles were examined by phase contrast microscopy and SEM. Three types of birefringent, crystalline particles formed: small, toroid particles with a characteristic swirled, lamellar substructure (5-10 microns); intermediate, lobed particles with 2, 4, or 6 radially striated lobes (20-50 microns); and large, spherical particles with radial striations (50-100 microns). The proportion of the three particle types was dependent on subtle variations in % solids, cooling rate, and the characteristics of the container. Formation of only the intermediate type of particle was previously reported, and those found in this study resembled previously published images of 1-butanol-precipitated starch, presumably formed by helical inclusion complexes. The development of these crystalline particles during slow cooling may influence the end-use properties of jet-cooked starches and starch-lipid composites.

Last Modified: 10/21/2014
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