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Susceptibility of Waxy Starch Granules to Mechanical Damage

¹USDA-ARS Western Wheat Quality Laboratory, Washington State University, Pullman, WA 99164-6394. 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. ²Department of Plant Sciences, Montana State University, Bozeman, MT 59717-3150. ³Corresponding author. Phone: 509-335-4062. Fax: 509-335-8573. E-mail: abettge@wsu.edu

Starch samples isolated from wheat flour that represented four possible waxy states (0, 1, 2, and 3-gene waxy) were subjected to crushing loads under both dry and wet conditions. Calibrated loads of 0.5–20 kg were applied to the starch samples and the percentage of damaged granules was visually determined. Under dry crushing conditions, starches containing amylose (0, 1, and 2-gene waxy) had between 1% (5-kg load) to 3% (15- and 20-kg load) damaged granules, whereas waxy starch (3- gene waxy; <1% amylose) began rupturing at 0.5-kg load (3.5% damaged granules) and had 13% damaged granules when ≥10-kg load was applied. Under wet crushing conditions, normal and partial waxy starch (0, 1, and 2-gene waxy) showed little difference in percentage of damaged granules when compared to the results of dry crushing. Waxy starch (3-gene waxy), however, showed substantially increased numbers of damaged granules: 12% damaged granules at 0.5-kg load, rising to 55% damaged granules at 15-kg load. The results indicate that waxy starch granules are less resistant to mechanical damage than normal starch granules. Furthermore, blends of normal and waxy wheats or wheat flours intended to have a particular amylose-amylopectin ratio will be a complex system with unique processing and formulation considerations and opportunities.