On the Hardness of Rice Endosperm

Abstract

The author has reported on the differences of endosperm tissue and of specific gravity of rice kernel in relation to the grain properties and has suggested that the endosperm density is an important charactor concerned in the grain property. However, the endosperm density is indicated most precisely by the hardness of endosperm, therefore this work was made to research the point-to-point variation of hardness of a single kernel and to explore the relation between hardness distribution and property of kernel. 1) Hardness Determination. Using Shimadzu Micro-Hardness Tester, a preloaded (15 g) diamond pyramid was forced into the even plane of kernel section for 13 seconds and the diagonal of quadrate impression was measured with a microscope, then Vickers hardness was calculated from the formula. 2) Hardness Distribution on Kernel Section. Hardness measurements were made on the transection of kernal at intervals of 150 p in dorso-ventral direction and of 100 p in lateral direction. According to the results on the section from middle of kernel (Fig. 1), the central point of section is rather soft and the middle region is the hardest and outer region from the middle becomes softer and softer, moreover, the region along the dorso-ventral line is somewhat softer than the adjacent region. This inclination of hardness distribution is essentially same on the sections from apical part and from basal part of kernel, except that every point of basal part is softer to a certain extent in comparison with the corresponding point of other parts. Hardness distribution. on the longisecton is recognized as the longitudinal connection of hardness diagrams of the transections as shown in Fig. 2. According to the facts above mentioned, the hardness distribution on the transection from middle of kernel is representative of hardness distribution of whole kernel and is represented by the hardness distribution along the dorso-ventral line and the lateral line crossing at the central point of the section. 3) Varietal Differences in Hardness Distribution. Diagrams of hardness distribution indicated by hardness along the dorso-ventral line and the lateral line are classified into two types by the hardness of central region (Fig. 3). Type I. (Hard Type) As shown in Fig. 3 (1-6), the central point is the hardest and outer region becomes softer on dorso-ventral and lateral line and the distinct difference can not be found between dorso-ventral line and lateral line. Indica varieties, glutinous varieties and some of upland varieties in Japan belong to this type and kernels of these varietes are assumably the hardest of all varieties. Type II. As shown in Fig. 3 (7-18), the central point is rather soft and the hardest part is the middle between the central point and aleulon layer and the region along dorso-ventral line is more or less softer than other region. Almost all varieties of Japonica are included in this type. With respect to the difference between dorso-ventral line and lateral line, this type may be subdivided into three groups. Type IIa. (Semi-Hard Type) The difference between dorso-ventral line and lateral line is rather small (Fig. 3, 7-11). Japanese varieties so-called "Koshitsu-Mai", some varieties of upland rice and some of Japonica varieties in foreign countries belong to this type. Type IIb. (Semi-Soft Type) The hardness along dorso-ventral line is softer than type II a and the difference between dorso-ventral line and lateral line is larger compared with Type IIa (Fig. 3, 12-16). Japanese varieties so-called "Nanshitsu-Mai" and some varieties of Japonica in foreign countries are included in this type. Type IIc. (Soft Type) The central point is very soft and dorso-ventral line is markedly softer than the lateral line (Fig. 3, 17-18). The varieties used for brewing in Japan (Saka-Mai) belong to this type and these varieties produce frequently white-core kernels (Fig. 6, 3). [the rest omitted]