Amylopectin fine structure: Mechanism of the long chain function

Xinyu Shen, Purdue University

Abstract

The sole impact of amylopectin long chains and internal structure on its functional properties was the research topic of this thesis. Greater and broader enthalpic transitions, greater increase in storage modulus and a denser and tighter gel microstructure after retrogradation were found in waxy rice starches with slightly higher proportion of long chains, indicating that more extensive intermolecular interactions were formed. The internal long chains of amylopectin are suspected to contribute to these intermolecular interactions. As a prerequisite to this hypothesis, the ability of internal chains to accommodate iodine as a turned or helical structure is regarded as an indication that internal chains either naturally exist in a helical form or have the flexibility to move around and form helices. Waxy and ae waxy corn starches were hydrolyzed by β-amylase for varied periods of time and the resulting β-dextrins, and the native structure, were exposed to iodine solution. The absorbance and the maximum wavelength of the absorbance were recorded. Two possible scenarios were proposed for the iodine internal chain complexation: (1) only external chains of native amylopectin bind iodine and hydrolyzed external chains allow internal iodine binding and (2) both external and internal chains of native amylopectin bind iodine. From the viewpoints of both chain length and helical conformational structure, the internal chains have the ability to bind iodine either because they are naturally synthesized in a turned helical form or they assume the helical structure under certain conditions, i.e. the removal of the external chains of amylopectin. Detailed fine structure information was obtained on waxy and ae waxy corn starches by varied time β-amylolysis followed by full β-amylolysis and debranching. This provided an explanation of the iodine binding results from the fine structure perspective. The “backbone” model was discussed as possibly a better explanation of the influence of the long chains of amylopectin on its functional properties, because they would provide more flexibility to the chains for the intermolecular interconnections on retrogradation. Gain in a mechanistic understanding of amylopectin structure related to its functional properties, in this case the role of the long internal chains of amylopectin on functionality, provides further information on tailoring structures to fit desired textural and nutritional starch functions.

Degree

Ph.D.

Advisors

Hamaker, Purdue University.

Subject Area

Food Science

COinS