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Genotype and environment influences on the amylolytic breakdown of wheat starch
L. COPELAND (1), M. T. Nhan (2). (1) Faculty of Agriculture and Environment, University of Sydney, Sydney, Australia; (2) College of Agriculture & Applied Biology, Cantho University, Cantho, Vietnam

The rate of amyloytic breakdown of starch is of interest for human nutrition, the formulation of animal feeds and industrial fermentations. Many factors are known to affect the rate of enzymic hydrolysis of starch, including granule size and intactness, amylose content, amylopectin fine structure, and the extent of starch gelatinization and retrogradation. However, there is limited information on the extent to which genotype and environmental factors during plant growth contribute to variability in starch digestibility. Therefore, starch was isolated from five commercial Australian milling wheat varieties that were grown in five locations in two seasons. Native starch granules and starch that was cooked and cooled were incubated <i>in vitro</i> with pancreatic alpha-amylase. The digestograms of the native granules showed significant variability between the five varieties, and also between the growth locations and seasons for each variety. There was less variability in the digestibility of starch that had been cooked. Statistical analysis of the data was performed to identify the contributions to variance from the effects of genotype, environment and their interactions. For native granules, genotype accounted for about 45% of the variance in the amount of glucose released in 2 hours, when about 5-10% of the starch was digested, but only about 15% of the variance at 24 hours (69-80% starch breakdown). Environmental effects, particularly temperatures during crop growth, were increasingly significant after 2 hours incubation. In comparison for cooked starch, genotype contributed about 60-70% of the variance in the amount of starch digested in 20 minutes and starch remaining after 2 hours. We conclude that temperatures during crop growth contributed to variability in the <i>in vitro</i> rate of breakdown of native granules after the initial stages of enzymic attack.

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