Differences in hydration between high hydrostatic pressure and heat gelatinization of rice starch

The water distribution of high hydrostatic pressure-gelatinized rice starch (HHGS) and heat-gelatinized rice starch (HGS) were investigated under various DGs from 20 % to 100 %, and the effect of hydration on the packing of liquid-crystalline polymer, helix-coil transition, ordered structure change and thermal properties were illustrated. The T₂ values at DG25%, the decreased characteristic dimensions of the lamellar structure, the increase of short chains, and the disappeared Maltese cross at DG50% for gelatinized rice starch indicated that the rice starch completed its hydration, which led to the entry of sufficient water to collapse of the crystalline lamellae and ordered structure. LF-NMR results showed that as DG increased, water molecules progressively entered into the tighter structure inside HHGS, and the T₂ value decreased and reached a minimum (0.086 ms) at DG75%, while the T₂ peak of HGS reached that position at DG25%. Therefore, the collapse of crystalline lamellae, the swelling of granules and the leaching of amylose of HHGS were limited, so the granules were more dispersed. The initial gelatinization temperature (T_o) and the wide flat DSC peak of HHGS were basically maintained as DG increased. However, the peak of HGS shifted toward higher temperatures and became sharpened and narrowed.