3.1 Effects of increased temperature on rice quality and
accumulation of grain storage materials
The temperature increase of 1.6 ℃ to 3.1 ℃ during grain-filling stage
induced various changes in the accumulation of storage materials during
grain development, and further affected the rice yield and quality
indicators. Results showed that tested rice yield in warming treatment
was 21% lower than that of the normal temperature treatment (data not
shown). Meanwhile, another significant change caused by warming is the
reduction in rice quality. Results indicated the increase in temperature
resulted in the increased grain thickness and decreased grain length.
There was no significant change in grain width, and aspect ratio of
grain shape. Compared with natural temperature, warming treatment
significantly increased rice chalky rate, chalky area and chalkiness.
Overall, the increase in temperature leads to overall deterioration in
the appearance quality of rice. In addition, elevated temperature has a
significant effect on milled rice rate and head rice rate. Compared with
the natural temperature, the milled rice rate and head rice rate were
decreased significantly. Increased temperature has led to the
deterioration of the appearance quality of rice. The increase in
temperature also caused significant changes in the rice cooking quality
indicators. Gelatinization characteristics peak viscosity (PKV),
hot-paste viscosity (HPV), and gelatinization temperature (GT) were
significant increased and the final viscosity was decreased (Table 1).
Starch and storage proteins are the main substances that constitute the
grain storage material. Under elevated temperature conditions, grain
total starch was increased significantly, of which amylopectin was
significant increased when responded to high temperature, while amylose
decreased significantly compared with normal temperature treatment, and
that further led to changes in the proportion of amylopectin /amylose.
The response of grain storage protein components to high temperature
appears as a significant increase in glutelin and a significant decrease
in prolamin. There results suggested high temperature during
grain-filling stage has a general negative impact on rice quality
parameters.