Chalky Grains Research Articles

Effects of air temperature and light on grain filling of an indica and a japonica rice (Oryza sativaL.) under controlled environmental conditions

Abstract The effects of air temperature and light on the grain filling of an indica (IR20) and ajaponica rice (Fujisaka 5) was studied in artificially lighted cabinets. Within the daily mean temperature range of 16° to 28°C, the higher the temperature, the faster the grains filled and matured. At 28°C, the upper grains of IR20 rice took 13 days to reach the maximum weight, whereas those of Fujisaka 5 took 18 days. The optimum daily mean temperature range to achieve maximum weight per grain was 19° to 25°C for IR20 and 16° to 22°C for Fujisaka 5. Apparently, IR20 rice is better adapted to higher temperatures during the ripening period than is Fujisaka 5 rice. More chalky grains occurred when the temperature was above or below the optimum range. Both day and night temperatures affected grain weight and grain quality. The daily mean temperature was found to be the most meaningful expression for describing the effect of temperature on grain filling. Low light intensity appeared to cause a slight delay in the grain filling of the whole panicle and a reduction in the percentage of filled grains on the lower branches. A combination of high light intensity and low temperature gave the best ripening grade (grain weight × percent filled grains).

Studies on Diagnosis of Rice Grains by Photometric Method : I. On light transmittance and reflectance by rice grains, and on a measuring instrument

An instrument was devised to measure the light transmitted or reflected by rice grains. And the possibility of using the value of transmittance or reflectance as a basis of objective method for estimating the quality of rice. A 6 gram sample of rice which laid in one layer in a glass container 66 mm in diameter was measured by the instrument using the same amount of normal grains as a standard of referrence. Various kinds of injured or inferior grains were tested for relative transmittance. The presence of chalkyness or abnormal coloring was indicated by a low relative transmittance as compared with normal grains. Experiments on the conditions of illumination revealed that illumination angle of 45° and light wave length of 420mμ might be most appropriate for measuring transmittance. The values were lowest at 420mμ wave length for all of the samples and increased with increased wave legth. Relative transmittance at 45° and 420mμ illumination, was 12% for chalky grain, 82% for white-core grain, and 95% for white-belly grain. The values for semi-chalky grain, milky-white grain, brown-discolored grain and green grain were intermadiate according to the degree of injury. The spectral transmittance curve for green grain was featured by a peak at 540 mμ and a drop at 660 mμ. The grains which have chalky tissues in their endosperm showed high relative reflectance as compared with the normal grain, whereas grains colored abnormally indicated low values. So, it may be said that the relative reflectance could not be used as an universal quality indicator. Another experiment revealed that the relative transmittance values for fissured grain and "hadazure-mai" or abraded grain were approximately 83% to 90% and 90% to 95%, respectively. It is concluded, therefore, that the relative transmittance measured by this method may be a simple and useful parameter for evaluating the quality of rice grain.

Studies on the Qualities of Rice Kernels

The grade of fullness of rice kernel is appropriately indicated by the specific gravity of the kernel. Among the kinds of rice grains, the rusty or greenish grains are inferior to the normal grains in specific gravity, and milk-white or partly chalky grains are inferior to the rusty or greenish grains but superior to the chalky grains. Moreover, among the normal grains, the grains which are superior in the specific gravity are superior in the lateral diameter, hardness and lustre to the grains which are inferior in specific gravity, and the depth of creases is shallower and the thickness of bran is thinner on the former than on the latter. Therefore, the qualities of rice grains are satisfactorily indicated by the specific gravity and the official standards of grading are indorsed fairly well by the specific gravity.