Abstract:

The objective of this study was to explore the changes in pasting properties, surface color and amylose content
of paddy rice with different moisture contents during simulated transportation at low, middle and high temperatures (which
fluctuated around 10, 20 and 30 ℃ , respectively and consequently to provide data support and theoretical basis for the
storage and transportation of paddy rice. For this purpose, newly harvested samples of paddy rice were adjusted to 14%,
16%, 18%, 20% and 22% moisture levels and thereafter stored at the above three temperatures for the measurement of
quality traits every 15 days for up to 2 months. Peak viscosity, hot paste viscosity, final viscosity, breakdown, and color
parameters a* and b* of paddy rice rose with prolonged storage time, whereas color parameter L* decreased. In addition,
setback increased firstly and then decreased to remain stable. Amylose content did not change significantly, except for a
decreasing pattern at the late stage of storage at high temperature. Peak viscosity, hot paste viscosity, and color parameters
a* and b* were affected significantly by initial moisture content (P < 0.05), and it also had a significant effect on final
viscosity and color parameter L* (P < 0.01, P < 0.05) but did not significantly influence breakdown or setback. Peak
viscosity, final viscosity, breakdown and setback and color parameter a* (P < 0.01, P < 0.05) as well as hot paste viscosity
(P < 0.05) were significantly impacted by storage temperature, while it had no significant influence color parameters L* or a*.
Moreover, peak viscosity and setback were positively correlated with each other. The more obvious the setback phenomenon
was, the poorer the eating quality of rice was. Amylose content was negatively correlated with each of the pasting properties
(P < 0.01) Therefore, low temperature can decrease the quality changes of high-moisture paddy rice. The initial moisture
content of paddy rice should be strictly controlled at 16% or a lower level for long-time (30 d) transportation due to dynamic
variations of temperature and humidity.

Key words: high moisture, paddy rice, pasting properties, surface color, amylose