GERMPLASM ENHANCEMENT OF MAIZE PROJECT (GEM)
Location: North Central Regional Plant Introduction Station, Ames, Iowa
Title: Characterization of Maize Amylose-extender (ae) Mutant Starches. Part II: Structures and Properties of Starch Residues Remaining After Enzymatic Hydrolyis at Boiling-water Temperature
Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2009
Publication Date: March 25, 2010
Citation: Jiang, H., Campbell, M., Blanco, M.H., Jane, J. 2010. Characterization of Maize Amylose-extender (ae) Mutant Starches. Part II: Structures and Properties of Starch Residues Remaining After Enzymatic Hydrolyis at Boiling-water Temperature. Carbohydrate Polymers. 80(1):1-12.
Interpretive Summary: Starch is an important ingredient for food and non-food applications and corn is the most important source of starch in the US. Starch consists of two components which include amylose, and amylopectin. Normal corn consists of approximately 20-30% amylose, and the remainder is amylopectin. One of the major corn genes is amylose extender, designated by the gene ae which produces predominately amylose which is known to be important for the production of resistant starch (RS). RS is a desirable ingredient of diets to manage obesity, and type 2 diabetes. An ae inbred developed by Truman State University and the Germplasm Enhancement of Maize (GEM) Project designated GEMS-0067 had 70% amylose content and RS between 39.4%-43.2% (vs. approximately 50% amylose and 11-19% RS for other existing ae corn line starches). An important objective of this study was to understand the mechanism of RS starch formation in the corn kernel, and to analyze the structural properties of RS residues that remained after enzymatic hydrolysis at boiling water temperature. Starch from GEMS-0067 kernels was found to have a larger proportion of large starch molecules (30.8-37.9%) compared to other existing ae corn inbred lines studied (14.7-20.2%). In addition, the RS residues were more concentrated in large filamentous starch granules at the outer edge of the granules. The results indicated that the RS from GEMS-0067 consisted of long chain double helical crystallites derived from amylose and intermediate components (branched starch molecules similar to amylose in weight). The crystallites had gelatinization temperature above boiling water and were resistant to starch enzymatic hydrolysis. Knowledge of the mechanism of RS starch formation may have potential impact for the development of new germplasm and health food products to manage obesity and diabetes.
GEMS-0067 maize ae-line starch developed by Truman State University and the Germplasm Enhancement of Maize (GEM) Project consisted of 39.4%-43.2% resistant-starch (RS), which was larger than the existing ae-line starches of H99ae, OH43ae, B89ae, and B84ae (11.5%-19.1%) as reported in part I of the study. The objective of this study was to understand the mechanism of the RS formation in the GEMS-0067 ae-line starch. In this study, we analyzed the structures and properties of the RS residues that remained after enzymatic hydrolysis of the ae-line starches at the boiling-water temperature. The RS residues consisted of two major components: large starch molecules of DP 840-951 with few branches (F2) and small starch molecules of DP 59-74 (F3). The RS residues of GEMS-0067 ae-line starches had more F2 contents (30.8-37.9%) than that of the existing ae-line starches (14.7-20.2%). All the RS residues displayed the B-type polymorph and high onset (100.7-107.7 C), peak (118.6-121.4 C), and conclusion (139.7-158.8 C) gelatinization-temperatures. After the maize ae-mutant starches were defatted with methanol, the RS contents decreased to 27.8-28.9% for the GEMS-0067 ae-line starches and 9.0-11.0% for the existing ae-line starches. The RS residue was more concentrated in rod/filamentous starch granules and at the outer layer of spherical starch granules. The results suggested that the RS was long-chain double-helical crystallites derived from amylose and intermediate component (IC) in the GEMS-0067 ae-line starch. The crystallites had gelatinization temperature above the boiling-water temperature and were resistant to enzymatic hydrolysis. Lipids in starch granules also reduced the susceptibility of enzymatic digestion at boiling-water temperature.