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Title: Resistant-starch Formation in High-amylose Maize Starch During Kernel Development

item JIANG, HONGXIN - Iowa State University
item LIO, JUNYI - Iowa State University
item Blanco, Michael
item CAMPBELL, MARK - Truman State University
item JANE, JAY-LIN - Iowa State University

Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2010
Publication Date: 6/1/2010
Citation: Jiang, H., Lio, J., Blanco, M.H., Campbell, M., Jane, J. 2010. Resistant-starch Formation in High-amylose Maize Starch During Kernel Development. Journal of Agriculture and Food Chemistry. 58:8043-8047.

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 be associated with several health benefits, such as reduction of glycemic index, less risk of developing type II diabetes, and potential reduction of obesity. The Germplasm Enhancement of Maize (GEM) Project, working in collaboration with Truman State University, released the inbred GEMS-0067 (PI 643420) in 2007. The objective of this study was to understand RS formation during kernel development of GEMS-0067 by studying the chemical and physical processes in starch granules at various stages of corn kernel maturity. Corn was harvested at 15, 20, 30, 40, and 54 days after pollination (DAP). It was found that RS content increased from 9-10% at 15 DAP, and reached a plateau of 32% RS at 40 DAP. Starch granule size increased from small spherical structures at 15 DAP, to larger and elongated granules (~7% elongated) at 40 DAP. This was associated with a simultaneous increase in apparent amylose content to ~88%. Knowledge of RS formation in the corn kernel is potentially important for the food industry to develop new methods of RS isolation, such as determining optimum timing of RS harvest and extraction. GEMS-0067 is an important source of publicly available germplasm for plant breeders to enhance maize RS development.

Technical Abstract: The objective of this study was to understand the resistant-starch (RS) formation during the kernel development of high-amylose maize, GEMS-0067 line. RS content of the starch, determined using AOAC Method 991.43 for total dietary fiber, increased with kernel maturation and the increase in amylose/intermediate component (IC) content of the starch. Gelatinization of the native starches showed a major thermal-transition with peak gelatinization temperature at 76.6-81.0 C. An additional peak (~97.1 C) appeared 20 days after pollination which developed into a significant peak at later dates. After removal of lipids from the starch, this peak disappeared but the conclusion gelatinization-temperature remained the same. The proportion of the enthalpy change of the thermal transition above 95 C, calculated from the thermogram of the defatted starch, increased with kernel maturation and was significantly correlated with the RS content of the starch (r=0.98). These results showed that the increase in crystallites of amylose/IC long-chain double-helices in the starch resulted in the increase in the RS content of the starch during the kernel development.