Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2005
Publication Date: 1/1/2006
Citation: Aboubacar, A., Moldenhauer, K.A., McClung, A.M., Beighley, D.H., Hamaker, Bruce R. 2006. Effect of growth location in the United States on amylose content, amylopectin fine structure, and thermal properties of starches of long grain rice cultivars. Cereal Chemistry. 83(1):93-98. Interpretive Summary: Rice cultivars grown in different regions of the country are subjected to different environmental conditions that impact grain quality. This research demonstrated that temperatures during grainfill have a significant impact on amylose content and starch structure; factors which influence sensory, cooking, and processing quality. Lower temperatures during grainfill were associated with greater amylose content, decreased long chain amylopectin, and increased short branched chain amylopectin. These changes in grain chemistry were associated with lower starch gelatinization temperature, likely due to decreased crystallinity of the starch granule. Cultivars differed in their sensitivity to growing environment for these starch parameters suggesting that this is under genetic control and can be selected for in a breeding program. These results elucidate how rice sensory, cooking, and processing quality are driven by the impact of genetics and the environment on grain chemistry.
Technical Abstract: Starch was isolated from kernels of 27 rice samples consisting of nine U.S. long grain rice cultivars grown in three different locations (Missouri, Arkansas, Texas). Amylose (AM) content of the starches and the fine structure of the respective amylopectin (AP) were determined and used to explain differences observed in gelatinization properties. The AM content of rice cultivars grown at the lower temperature Missouri location increased 0.4-3% and 0.5-4% when compared with the same rices grown in Arkansas and Texas, respectively. AP values of the rice samples were isolated, debranched, and separated by low-pressure size-exclusion chromatography. The eluted AP linear chains were divided into three fractions to represent extra long (FrI), long (FrII), and short chains (FrIII). The corresponding average degree of polymerization (DPn) at the peaks of fractions FrI, FrII, and FrIII were 100, 39, and 16, respectively. Total carbohydrate analysis of the fractions indicated that cultivars grown in Missouri had a consistently higher proportion of FrIII and lower proportion of FrII as the same cultivars grown in Arkansas and Texas. Furthermore, the Missouri samples showed a shift toward shorter DPn in FrII and FrIII and had more of the shortest chain components (DPn<16) of AP. The proportion of FrI did not follow a trend and varied depending on the cultivar and across location. Thermal analysis indicated that the higher temperature growth environments (Arkansas and Texas) resulted in higher onset, peak, and heat of gelatinization of the starches, suggesting longer cooking time and higher heat requirement. Overall, the data support the nonfield findings of other researchers that higher growing temperature results in AP with more DPn short chains that are within a range of DP>10 to form consistent crystallites, and thus results in higher gelatinization temperatures and enthalpies.