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Pasting Process in Rice Flour Using Rapid Visco Analyser Curves and First Derivatives

¹USDA-Agricultural Research Service, Richard B. Russell Agricultural Research Center, P.O. Box 5677, Athens, GA 30604-5677. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. E-mail: Fmeadows@shirelabs.com. Phone: 301-838-2666. Fax: 301-838-2501. ³Current address: Shire Laboratories, Inc., 1550 East Gude Drive, Rockville, MD 20850.

The objective of these studies was to gain a better understanding of the pasting process in rice. We chose six different medium grain rice flour samples with amylose contents of 0.41–24.9% and protein contents of 4.89–10.65%. By using the first derivative of Rapid Visco Analyser (RVA) curves, changes in the pasting rates could be obtained. We found that samples containing low amylose contents (CM101 [CA] 0.41% amylose and 7.04% protein) exhibited a single smooth transition during pasting. Pastes from all other samples, M201 (TX), Nato (LA), Koshihikari (CA), Mercury (LA), and Nanking Sel (LA) with higher amylose contents (10.65–24.9%) underwent multiple phase transitions and rate changes before the peak viscosity. Disruption of disulfide linkages using dithiothreitol (DTT) led to a decrease in the rate of the single pasting step observed for CM101 (CA). Rice containing larger concentrations of amylose showed an increase in the first, but a decrease in subsequent steps. Our data suggests that amylopectin and protein are mutually important in the initialization of pasting in rice. At later stages of pasting, amylose and its complexes seem to become important.