Selected quality attributes of paddy rice as affected by storage temperature history

Five experimental storage conditions were designed to study the effect of storage temperature on paddy rice. Three of the conditions were designed with varied order of temperature but with the same overall exposure. The five conditions were: (i) 15°C for 12 months (low-temperature condition, LC); (ii) 30°C for 12 months (high-temperature condition, HC); (iii) 15°C for 6 months followed by 30°C for an additional 6 months (low–high-temperature, LH); (iv) 30°C for 6 months followed by 15°C for an additional 6 months (high–low-temperature, HL); and (v) alternating 2-month intervals at 15°C and at 30°C for a total of 12 months (alternating low–high-temperature, ALH). The resultant quality attributes of the stored rice samples were measured and compared at intervals over the 12 months. For all samples, fat acidity increased during storage, while germ cell volume and cell gap decreased. The changes were greater after exposure to high temperature than after exposure to low temperature. However, the overall results for the samples stored at varied-temperature conditions showed only slight differences in fat acidity, as well as in germ cell volume and cell gap. In addition, the overall results for these samples yielded only slight differences in polyphenol oxidase activity, peroxidase activity, pasting parameters, and cooked rice quality attributes (water uptake ratio, volume expansion ratio, hardness, and springiness). These results suggest that order changes of high- and low-temperature conditions can affect the intermediate quality of the stored rice but have limited influence on the final quality.