Studies on Diagnosis of Rice Grains by Photometric Method : IV. Estimation of milling degree and quality evaluation of milled rice

Abstract

The author has reported in the previous papers a photometric method evaluating the quality of hulled rice using Inspector. In this experiment, some methods for estimating the quality of milled rice and the degree of milling were investigated. Several characteristics of rice grain were also studied upon the light transmittance with special reference to wave length and kernel characters. The results are summarized as follows: 1. Rice bran layers specifically absorbed the light of short wave length. Milled rice, therefore, transmitted greater amount of light in short wave range as compared with hulled rice. 2. Relative transmittance values (RTV) for the light in short wave range (420 nm) were markedly increased as the milling degree of kernel increased. The increment curve of RTV with milling was parabolic and flattened at the completion of milling (around 84% of milling degree). 3. These results suggested a possibility to estimate the degree of milling photometrically. So, the author proposed a calculating formula by which the degree of milling may be estimated regardless of variety and grain character. The proposed method was tested against the weighing method so far used. The result indicated the reliability of this new method. 4. On the other hand, long wave lights especially in near infra-red range were easily transmitted through the bran layers of rice kernel, but were diffused and reflectcd by opaque tissues in rice endosperm as were the lights of other wave length. 5. Therefore, a photometric method using a near infra-red ray (710 nm) was proposed for estimating the translucency of kernel and for evaluating the quality or the degree of ripening of rice endosperm without being influenced by bran layers. 6. RTV of milled rice was negatively correlated with the amount of imperfect kernels, but showed a highly positive correlation with RTV of hulled rice.