Submitted to: Corn Utilization Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 9, 2004
Publication Date: June 9, 2004
Citation: Felker, F.C., Fanta, G.F. 2004. Crystalline particles formed during cooling of steam jet-cooked cornstarch - a variety of forms with potential applications. (Abstract) Corn Utilization Conference, June 9, 2004, Indianapolis, Indiana. p. 38. Technical Abstract: The development of a new starch-oil composite technology at NCAUR employing the technique of excess steam jet cooking has opened the door to a renewed interest in steam jet cooking as a starch processing method. Specifically, the excess steam method used in this technique affords much more mechanical shear and thus more complete dissolution of starch components than the traditional thermal cooking mode. Whereas the inclusion of an oil or lipid phase in the inlet stream allows the production of a wide variety of products for food, industrial, or agricultural applications, basic research on the jet cooking process has revealed the formation of an interesting class of starch crystallites which may have significant commercial potential. When cornstarch is suspended in water in a certain concentration range, cooked with an excess steam jet cooker, and cooled slowly (over a period of 4 hours or overnight), a variety of crystalline particles are observed, the nature and quantity of which depends on the starch concentration, the cooling rate, stirring conditions, and other factors. These include toroidal crystallites, 2- or 4-lobed crystallites, and spherocrystals. Particles are photographed using phase contrast microscopy, birefringence (crossed polarizer) light microscopy, and by scanning electron microscopy (SEM) after critical point drying from ethanol. The toroidal particles are about 2-8 micrometers in diameter, with a surface pattern of spiral striations and a weak birefringence. Their thickness, size, and the depth of the central depression varies considerably according to conditions, but within a given experiment there is surprisingly little variation in their appearance or size. The 2- or 4-lobed crystallites vary in size and degree of development of the lobes. They show a characteristic banded birefringence pattern. Usually they occur in combination with other types of crystallites, but specific conditions can result in them being the only type present. The larger, more spherical crystallites have a characteristic radial striation pattern when viewed under phase contrast, and also have a striking concentric band pattern of birefringence. SEM reveals a characteristic pile-like surface texture. Evidence suggests that the lobed crystallites develop into these mature, spherical forms. It is usually possible to separate the large spherical and lobed crystallites from the smaller toroidal ones by simple sedimentation. This has allowed the characterization of specific classes of crystallites by X-ray diffraction, FTIR, and analysis of complexed lipids. These crystallites are stable in boiling water, and they can be dried and rehydated. We have successfully graft polymerized polyacrylonitrile to them, and their shape is retained. Experiments suggest that large-scale production may be feasible. Their ease of production from an abundant, renewable resource, along with their large surface area and ability to be chemically modified, makes them an excellent opportunity for developing new applications for starch.