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

Abstract

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 (To) 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.