Location: Plant Introduction ResearchTitle: Formation of Elongated Starch Granules in High-amylose Maize Author
Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2009
Publication Date: 4/12/2010
Citation: Jiang, H., Horner, H.T., Pepper, T.M., Blanco, M.H., Campbell, M., Jane, J. 2010. Formation of Elongated Starch Granules in High-amylose Maize. Carbohydrate Polymers. 80(2):534-539. Interpretive Summary: In the human digestive system, a portion of starch known as resistant starch (RS) cannot be digested and absorbed in the small intestine and is passed to the large intestine for bacterial fermentation. RS from high-amylose maize has been reported to have many health benefits such reducing the glycemic index, less risk of developing type II diabetes, and reducing obesity. An important goal of the USDA-ARS Germplasm Enhancement of Maize Project (GEM) is to broaden and enhance the germplasm base to ensure a safe and healthy food supply. Starch from the GEM high amylose maize line GEMS-0067 contains up to 32% elongated starch granules which is higher than conventional amylose lines (~7% elongated granules). The elongated starch granules are important cellular structures containing RS. The objective of this study was to understand the structure and formation of these elongated granules using light, confocal laser scanning, and transmission electron microscopic (TEM) images. The results of these observations led us to propose a mechanistic model for the formation of RS which included the interaction and fusion of smaller granules that began in the early stages of granule development. Knowledge of how elongated starch granules develop, and their role in RS content have potential impact in the food industry for new methods of RS isolation and/or processing. Plant breeders may also benefit by identifying and improving germplasm with enhanced levels of RS that will ultimately benefit the consumer with a safe and healthy food supply.
Technical Abstract: GEMS-0067 maize starch contains up to 32% elongated starch granules much higher than amylose-extender (ae) single-mutant maize starch (~7%) and normal (non-mutant) maize starch (0%). These elongated granules are highly resistant to enzymatic hydrolysis at 95-100 C, which function as resistant starch (RS) and provide health benefits, including interventions of diabetes and colon cancer. The structure and formation of these elongated starch granules, however, were not known. In this study, light, confocal laser-scanning, and transmission electron (TEM) microscopies were used to reveal the structure and formation of these elongated starch granules. The TEM images showed fusion through amylose interaction between adjacent small granules at the early stage of granule development. A mechanistic model for the formation of elongated starch granules and RS is proposed.