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Title: Characterization of Maize Amylose-Extender (ae) Mutant Starches. Part I: Relationship Between Resistant Starch Contents and Molecular Structures

item Blanco, Michael

Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2008
Publication Date: 11/4/2008
Citation: Li, L., Jiang, H., Campbell, M., Blanco, M.H., Jane, J. 2008. Characterization of Maize Amylose-Extender (ae) Mutant Starches. Part I: Relationship Between Resistant Starch Contents and Molecular Structures. Carbohydrate Polymers. 74(3):396-404.

Interpretive Summary: An important objective of the Germplasm Enhancement of Maize (GEM) is to identify, characterize, and develop adapted germplasm with value-added traits. Germplasm derived from the GEM Project and Truman State University included a Guatemalan breeding cross, GUAT209:S13ae, found to have starch genes that enhanced the level of amylose (a component of starch) to more than 70%. Additionally, the level and composition of amylose starch found in three inbreds derived from GUAT209:S13ae ("GEM lines") was associated with increased levels of resistant starch (RS). RS resists digestion in the small intestine and is of interest to the food and health industry since it lowers the glycemic index, reduces obesity, and is presently undergoing further research for diabetes and colon health. A comparative analysis was made to characterize the RS from GUAT209:S13 relative to other sources of starch from public sources of corn germplasm with amylose-extender (ae) genes. The RS content, measured using the Association of Analytical Communities (AOAC) method 991.43, ranged from 39.4%-43.2% for the three GEM lines, while RS isolated from four public inbred corn lines (H99ae, OH43ae, B89ae, and B84ae), ranged from 11.5%-19.1%. The three GEM line starches had larger apparent (83.1-85.6%) and absolute amylose-content (57.4-62.6%) than the starches of the public ae lines (61.7-67.7% and 35.5-44.7%, respectively). Other analyses of GEM line starches included starch thermal and gel permeation properties. The results indicated that the crystalline structure of the three GEM lines was highly resistant to enzyme hydrolysis, and displayed two times greater RS content than the current publicly available inbreds. The impact of this research includes new sources of genetic diversity made available to plant breeders to develop corn varieties with enhanced levels of amylose and RS that will ultimately benefit the consumer with a safe and healthy food supply.

Technical Abstract: Endosperm starches were isolated from kernels of seven maize amylose-extender (ae) lines. The resistant starch (RS) contents, measured using AOAC method 991.43, showed that three new ae-mutant starch lines developed by the USDA-ARS Germplasm Enhancement (GEM) and Truman State University had larger RS contents (39.4%-43.2%) than the four other inbred starch lines, H99ae, OH43ae, B89ae, and B84ae, (11.5%-19.1%). The pedigrees of the three ae-mutant lines from the GEM Project were derived from a Guatemalan breeding cross and were as follows:[GUAT209:S13 × (OH43ae×H99ae) B-B-4-1-2-1-1, GUAT209:S13 × (OH43ae×H99ae) B-B-4-4-2-1-1, and GUAT209:S13 × (OH43ae×H99ae) B-B-4-4-2-1-2]. These three new starch lines had larger apparent (83.1-85.6%) and absolute amylose-content (57.4-62.6%) than the other ae starch lines (61.7-67.7% and 35.5-44.7%, respectively). The RS content of the ae-mutant starch lines was positively correlated with both the apparent and the absolute amylose-content of the starch lines with correlation coefficients of 0.99 and 0.96, respectively. Gel permeation chromatograms also revealed that all seven ae starch lines contained large proportions of amylose and the intermediate components (IC). The starches contained 22.4%-52.0% IC. All seven starch sources displayed similar onset gelatinization temperatures (64.5-65.8 C). The starches of the three new lines displayed higher conclusion gelatinization temperatures (122.0-130.0 C) than that of the other four inbred lines (100.5-105.3 C). The results indicated that the crystalline structure of the three new ae-line starches was retained after heating at ~100 C during the analysis of RS content. Because the B-type crystalline structure of the ae-mutant starch line was highly resistant to enzyme hydrolysis, starches the new maize ae-lines displayed greater RS content.