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Submitted to: Journal of Rheology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/17/1995 Publication Date: N/A Citation: N/A Interpretive Summary: Industrial methods of processing starch not only subject the starch to high temperature, but also to high shear and mechanical work. To obtain better products and better quality control and to increase the utilization of starches the effects of such processes upon the molecular structure and the flow behavior of processed starch dispersions need to be evaluated. This work examined how a molecular property of dissolved starch, the intrinsic viscosity, of three typical corn starches was affected by industrial processing methods (jet-cooking, autoclaving) and how such processing affected the ability of cooked starches to flow. The decreases in intrinsic viscosity and changes in flow behavior were significantly different for the different starches. This information is of use to scientists interested in devising improved food formulations and to industrial processors of starches. Technical Abstract: A waxy, a dent, and a high amylose starch were subjected to thermomechanical processing of varying degrees of severity. These treatments ranged from gentle dissolution in 90 percent DMSO to autoclaving, at temperatures up to 180 degrees C, to jet-cooking. The treatments had major effects on viscosities of the starch dispersions and in particular on the intrinsic viscosities, which were determined to provide a relative measure of the molecular sizes of the processed starches. The intrinsic viscosities, from the least severe treatment to the most severe treatment were: 220 and 91 ml/g; 181 and 104 ml/g; 105 to 80 ml/g, respectively for the waxy, dent, and high amylose starches. An unexpected characteristic of processed waxy maize was that the viscosity of 6 percent dispersions was extremely sensitive to intrinsic viscosity changes in the narrow range of 180 to 165 ml/g. In contrast, viscosity of waxy maize dispersions were relatively insensitive to changes in the lower intrinsic viscosity values (<160 ml/g) caused by more severe treatments. Dispersions of jet-cooked waxy maize exhibited Newtonian flow, jet-cooked dispersions of high amylose starch did not. |
