Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 1998
Publication Date: N/A
Interpretive Summary: When mixtures of oil, water, and starch are treated with high pressure steam, using a processing technique known as steam jet cooking, new products having interesting and commercially useful properties are obtained. Products of this type have been given the trademark of Fantesk by the USDA. Fantesk products contain microscopic droplets of oil suspended in a water dispersion of starch; and these oil droplets do not separate or coalesce, even when the dispersion is dried or allowed to stand for prolonged periods of time. We have found that this unusual stability is caused by the spontaneous formation of a thin layer of shell of starch around each individual oil droplet during the preparative process. These shells have been observed microscopically. Discovery of these starch shells opens up new fields of application for Fantesk in foods, cosmetics, lubricants, adhesives, and drug delivery systems.
Technical Abstract: Starch-oil composites were prepared by passing aqueous mixtures of starch and soybean oil (100:40, by weight) through a steam jet cooker operating under excess steam conditions. Dilution of jet cooked dispersions with a 20-fold excess of water reduced the viscosity and caused a lipophilic fraction with low specific gravity to separate from the dispersion. This fraction could be collected and washed with water without coagulation of oil droplets. Microscopy showed that this fraction was comprised of oil droplets surrounded by thin films of starch at the oil-water interface. The most detailed view of these spherical starch films was obtained by scanning electron microscopy, after isolating films by ethanol precipitation and critical point drying. Films prepared from normal food grade cornstarch, waxy cornstarch and high amylose cornstarch were compared. Interfacial starch films were observed not only when aqueous mixtures of starch and soybean oil were co-jet cooked, but also when starc solutions were first jet cooked and then blended with soybean oil in a separate step. Starch films were also observed with lipophilic materials other than soybean oil, for example, mineral oil, paraffin wax, and alpha- tocopherol. We have considered the question of why these starch films are spontaneously formed at the droplet interface, despite the fact that starch is not surface active and no surface active materials are used during the preparation. A reasonable explanation is provided by the known thermodynamic properties of aqueous polymer solutions at interfaces. Formation of a layer of polymer at an oil water interface (prewetting) occurs when adsorption of polymer leads to a reduction in interfacial tention and when the solvent for the polymer is relatively poor.