Rice Ageing. I. Effect of Changes in Protein on Starch Behaviour

Pasting properties of starch were affected by storage at 37 °C; the most significant changes were seen in peak viscosity and breakdown. In contrast, storage at 4 °C retarded the changes. The composition of the leachate from the RVA pastes was significantly affected by storage temperature ( P < 0.01) with a lesser proportion of amylose in samples stored at 37 °C. Thus, ageing was associated with decreased leaching of starch and particularly amylose. Protease treatment increased the ratio of amylose to amylopectin in the hot‐water soluble fraction significantly ( P < 0.05) for samples following storage at 37 °C while the ratio did not change for samples stored at 4 °C. Of greater significance was that the ratio was the same for samples stored at both temperatures following protease treatment. Similarly, after protease treatment the peak temperatures of the gelatinisation endotherm ( T p ) of samples stored at 37 °C were identical to those of the samples stored at 4 °C. Protein was considered an important factor in the ageing process and the changes in proteins associated with storage were investigated. Higher storage temperature caused a reduction in the amount of prolamin and glutelin in the propanol‐extractable fractions.