Palatability and Bio-Functionality of Chalky Grains Generated by High-Temperature Ripening and Development of Formulae for Estimating the Degree of Damage Using a Rapid Visco Analyzer of Japonica Unpolished Rice

Effects of Binding between Ca in Hard Water and Phosphorus in Amylopectin on the Qualities of Boiled Rice and Rice Noodle Prepared by Soaking and Boiling in Hard Water

Recently, global warming has led to an increase in chalky rice grains. This has consequently resulted in the deterioration in quality of rice products. Although we previously reported that hard water, rich in Ca, is useful for the quality improvement of high-temperature-damaged rice grains, the mechanism was not elucidated sufficiently. Therefore, we used various kinds of rice cultivars, from waxy to high-amylose ones, for soaking and boiling in hard water and compared physical and chemical properties of the products. It was shown that the degree of quality improvement, such as final viscosities in pasting property, and textural properties of boiled rice, was more remarkable for high-amylose rice than low-amylose rice. As we found that the phosphorus contents showed positive correlations with amylose and long chains of amylopectin, we estimate that the effects are mainly due to binding of calcium and phosphorus. Because that high-amylose or long-chain-rich amylopectin rice cultivars showed high calcium contents in rice products, these rice cultivars would be very useful to supply calcium through dietary intake via hard water cooking.

Effects of exogenous zinc (ZnSO4·7H2O) on photosynthetic characteristics and grain quality of hybrid rice

Rice is an important food crop and zinc (Zn) is a beneficial microelement. However, there are few reports on the effect of zinc on yield and physiological characteristics of rice. In this study, exogenous zinc (ZnSO4·7H2O) was applied on plant to explore the effects of zinc on rice yield, quality and photosynthetic capacity. The results showed that appropriate concentration of zinc could increase the net photosynthetic rate (Pn) of rice leaves, and Zn2 (2 mg/L ZnSO4•7H2O) treatment was the most significant. However, the Zn treatment had no positive effect on rice yield except under the concentration of Zn2. Meanwhile, the result showed that Zn treatment could increase chalkiness degree (CD) and chalky grain rate (CGR), decreased amylose content (AC), increased protein content and changed protein composition of rice. The above indexes were most significant in Zn2 treatment. In addition, the Zn2 treatment significantly increased rapid viscosity analyzer (RVA) of rice. In conclusion, the results of this study suggested that Zn treatment could enhance the photosynthetic capacity of rice leaves, and improve the processing quality, taste quality and nutritional quality of rice. However, it will have a negative impact on the appearance quality of rice and cannot be used to increase rice production. This study will provide a basis for the application of zinc in rice production.

Effects of Hard Water Boiling on Chalky Rice in Terms of Texture Improvement and Ca Fortification

In the present paper, we investigated the characteristics of chalky rice grains generated by ripening under high temperature and compared them with whole grains. We evaluated 14 unpolished Japonica rice grains harvested in Japan in 2021, and these samples (original grains) were divided into two groups (a whole grain group and a chalky grain one). We found that not only activities of endogenous amylase and proteinase, but also cell wall-degrading enzymes, such as xylanase and cellulase, changed markedly between chalky grains and whole grains. Using rice grains blended with 30% of chalky grains as the material, we compared the sugar and mineral contents and textural properties of the rice grains soaked and boiled in either ordinary water or hard water, such as Evian or Contrex. It was shown that xylanase, in addition to amylase and proteinase, may play an important role in changing the texture of the boiled chalky rice grains. For the sake of preventing the above-mentioned deterioration in the texture of boiled grains of chalky rice, we tried to use hard water, such as Evian or Contrex, to soak and cook the chalky rice grains. It was shown that the hard water was useful for the prevention of texture deterioration of the boiled rice grains due to inhibition of the activities of endogenous hydrolytic enzymes, such as α-amylase, β-amylase, proteinase, and xylanase. Furthermore, we found that the hard water was useful in increasing the calcium absorption through the meal by 2.6 to 16.5 times.