Relationships between physicochemical, morphological, thermal, rheological properties of rice starches

Abstract

The starch separated from 19 different indica rice cultivars was evaluated for physicochemical, morphological, thermal and rheological properties. The relationships between the different properties of starches were determined using Pearson correlation analysis. The amylose content of starches from different rice cultivars differed significantly. PR-103 starch showed the lowest amylose content (4.1%), whereas PR-113 starch showed the highest (16.4%). The starch granular size ranged between 1.5 and 5.8 μm. The starch granules were observed to be polyhedral and irregular in shape. Starch from PR-113 and RYT-2492 mainly consisted of large size polyhedral granules while that from PR-103 and IR-64 had small size irregular granules in a fairly large number. IR-64 and Sasyasree starches showed higher gelatinisation enthalpy (Δ H gel) of 13.81 and 12.32 J/g, respectively, whereas PR-111 starch showed the lower Δ H gel (8.09 J/g). Δ H gel showed a positive correlation with transition temperatures (onset, T o; peak, T p; conclusion, T c) and correlation was strongest with T c ( r=−0.651, p≤0.01). Peak viscosity showed positive correlation with swelling power ( r=0.491, p≤0.05) and negative correlation with pasting temperature ( r=−0.434, p≤0.05). Final viscosity and setback also showed a positive correlation with amylose content; however, correlation was stronger with setback ( r=0.464, p≤0.05 and 0.614, p≤0.01, respectively). Final and setback viscosity showed negative correlation with swelling power. T o, T p and T c showed significant positive correlation with pasting temperature ( r=0.441, 0.472, 0.483, respectively, p≤0.05) and light transmittance (measured after 0 and 24 h). Peak viscosity was positively correlated to transmittance measured after different storage duration. Transmittance and syneresis measured after 72 h showed negative correlation with each other ( r=−0.499, p≤0.05). Pasting temperature was negatively correlated to peak, trough and final viscosity; however, correlation between pasting temperature and trough viscosity was stronger ( r=−0.553, p≤0.01). The syneresis measured after 72 h showed a significant negative correlation with swelling power. The syneresis showed negative correlation with transmittance and the correlation became stronger with the increase in storage duration.