Influence of microwave treatment on the structure and functionality of pure amylose and amylopectin systems

Pure granular amylose (AM) and pure granular amylopectin (waxy) starch (AP) granules have the high nutritional value in food industry. Effects of microwave treatment (400 W/g DW, 1–8 min) on the structure and properties of transgenic AM granules and AP granules were investigated in direct comparison. Microwave treatment, especially during the first 3 min, decreased the molecular weight of molecules in both the AM and the AP samples. The crystallinity of AM starch initially increased from 15.6% to 20.6%, which was associated with the formation of new V_h-type crystals. After that, crystallinity decreased alongside to 11.3% with the complete disruption of B-type crystals. In contrast, the crystallinity of AP starch initially decreased from 18.9% to 10.8% followed by an increase to 20.0%. Upon prolonged treatment of AM granules, the resistant starch and water solubility was significantly increased. Our data demonstrate notable different microwave-dependent reorganization patterns for pure granular AM and AP molecules as native granular systems, which is helpful to the improvement of functionality of these two starches.