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 (Tp) 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.