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

Abstract

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.