Changes in Pasting Behaviour of Rice during Ageing

Fifteen varieties of rice belonging to six quality types were stored at room temperature for 51 months. Their Brabender viscograms were determined at intervals for several slurry concentrations. The progressive viscogram patterns showed several distinctive features: first, the paste breakdown steadily decreased with time of storage; simultaneously there was a steady increase in setback, in the temperature or heating time at which the peak viscosity (P) appeared, in the minimum value of P at which a breakdown appeared, and in the P value at which the setback became zero. Clearly ageing rendered the rice substance progressively more organized and resistant to swelling and disintegration. Second, the changes were relatively rapid at first, gradually slowing down later, but did not show signs of being halted even after 4 years, suggesting that ageing of rice probably had no definite end-point. Third, despite the ageing changes, rice of different quality types broadly maintained their inter-quality differences throughout the storage period. Fourth, it is remarkable that the cold-paste:hot-paste viscosity ratio in the samples remained virtually unchanged throughout even while all other viscogram indices changed with storage time. Considering the viscographic technique, the results confirmed that (i) the fixed-P system is far superior to the fixed-concentration one and (ii) breakdown is the primary viscogram index.