Thermal and mechanical properties of concentrated rice starch gels of varying composition

Abstract

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 δ and amylose content ( r = −0.75, p < 0.01). All high-amylose (>29%) rice starch gels exhibited tan δ 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 C 2.2–2.9 ( 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°C) by calorimetry indicated that granular lipids retarded this process; the effect was more pronounced for low-amylose rice starches.