Effect of heat-moisture treatment on structural and thermal properties of rice starches differing in amylose content.

摘要

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat-moisture treatment (HMT) at 100 degrees C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat-moisture treatments on structural and thermal properties of these 3 rice starches was investigated. HMT did not change the size, shape or surface characteristics of rice starch granules. The A-type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short-range molecular ordered regions to amorphous (RSA) areas of heat-moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V-amylose-lipid complexes was clearly observed in all treated Chiang rice starches. The peak became progressively stronger with increases in moisture levels. DSC of all treated rice starches showed a shift of the gelatinization temp. to higher values. Increasing moisture levels of the treatments increased the onset gelatinization temp. (To), but decreased the gelatinization enthalpy ( DeltaH) of rice starches. A broad gelatinization temp. range (Tc-To) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT27 (HMT at 27% moisture level). Additionally the (Tc-To) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.