Susceptibility of waxy starch granules to mechanical damage

Starch samples isolated from wheat flour that represented four possible wavy 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.