THERMAL AND MECHANICAL-PROPERTIES OF CONCENTRATED RICE STARCH GELS OF VARYING COMPOSITION

The thermal and mechanical properties of concentrated (25-35% w/w) starch gels of 43 non-waxy rices, varying in their amylose content and gelatinization characteristics, were investigated by small amplitude oscillatory shear measurements and differential scanning calorimetry. The storage modulus (G') of freshly prepared gels increased exponentially with increasing amylose content. An inverse linear relationship was also found between tan delta and amylose content (r = -0.75, p<0.01). All high-amylose (>29%) rice starch gels exhibited tan delta values less than 0.1, indicating well cross-linked networks. At starch concentrations within 10-25% (w/w), the dependence of storage modulus on concentration followed power law relationships; G' varies as C2.2-2.9 (r>0.96, p<0.01). Changes in gel rigidity (G') upon storage were not solely dependent on amylose content. Kinetic experiments on staling of gels (35% w/w, 8-degrees-C) by calorimetry indicated that granular lipids retarded this process, the effect was more pronounced for low-amylose rice starches.