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United States Department of Agriculture

Agricultural Research Service

Title: Estimation of the Intrinsic Birefringence of the A, B and V Crystalline Forms of Amylose

item Shogren, Randal

Submitted to: Starch
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2009
Publication Date: 10/22/2009
Citation: Shogren, R.L. Estimation of the Intrinsic Birefringence of the A, B and V Crystalline Forms of Amylose. Starch. 61(1):578-581.

Interpretive Summary: This research has increased scientific knowledge of how properties of corn starch based fibers and films can be predicted and measured. When corn starch films are stretched, the starch molecules become oriented in one direction and strength and flexibility improve markedly. However, it is currently difficult to measure exactly how much the starch molecules have been oriented. In this research, the refractive index of a fully oriented starch was calculated. This enables the measurement of orientation for real starch films and fibers and the ability to determine if a test process is achieving optimal improvement in the film. This information will benefit researchers who are involved in making improved starch based materials for applications in areas such as biodegradable packaging, personal hygiene, biodegradable packaging, sutures, medical implants, and responsive "smart" materials.

Technical Abstract: Optical birefringence (Delta n) for A, B, Va, Vh amylose crystals were calculated by vector summation of bond polarizabilities. Orientation of the O-H bond vectors in these amylose crystals is not well understood so results are given for likely O-H conformers. For B amylose, Delta n ranges from 0.043-0.058 with Delta n = 0.048 for O-H conformations considered likely from previous molecular modeling studies. This is slightly higher than experimental values of 0.031-0.037 determined previously for highly oriented amylose films. Predicted values of Delta n for A amylose were similar to B amylose while Delta n for V amyloses were smaller (-0.04-0.0). These estimates of the intrinsic birefringence of amylose crystals should be helpful in estimating the degree of orientation for starch films and fibers processed by a variety of methods.

Last Modified: 06/24/2017
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