Studics on the Strain and the Cracking of Rice Kernels under Drying (III)

Particularly on the Movement of Marked Point and the Shrinkage Strain on the Surface of Kernel of Rough Rice

Abstract

This study was done to measure the movement of the marked point and the shrinkage strain at the surface of brown rice kernels in the rough rice under drying. The measured planes were the length-width, the length-thickness and the width-thickness plane of the brown rice kernels. The authors made four (or six) small pits into very shallow layer of the endosperm of brown rice by fine needle from the surface of kernel of rough rice. The x-ray photographs were taken at a regular intervals during the drying of rough rice. So the authors put the least amount of 38% Urografin solution (contrast medium of blood vessel) into the inside of those pits and increased the contrast of reflex of x-ray photograph. Then, a small amount of the silicon grease was put on those pits and kept off evaporation from that place during drying. Those processed pits were used as marked point.
The following results were obtained through this study.
1. The marked points on the surface of the brown rice involved in the rough rice under drying were displaced to-
Three demensional center of shrinkage under drying: It was pressumed from the movement of marked points that the three dimensional center of shrinkage of rice kernel displaced to the fixed point 40% for the max. -length from the basal end on the center line of cellular disposition of rice kernel. It was suposed that this point was important to cause rice crack, and cracked position, and also to produce large shrinkage strain on the germ-end and perpendicular to long-axis on central part of rice kernel.
2. The principal strain on the length-width plane. The maximum principal strain: This strain was observed in parallel direction to the long-axis of this plane. In the case of sample 1 and 2, this strain was found in the direction of compression, and those values were enlarged with an increase during the drying time. In the case of sample 3, this strain was found in the direction of tension at early stage of drying. But some of them were found in the direction of tension until the end of drying.
The minimum principal strain: This strain on the central part of this plane showed smaller value than the one on the other part. This strain was increased in the part of dorsal side, the central part and the ventral side of the kernels in order. And the value of the ventral side showed double of the dorsal side.
3. The shrinkage strain on the length-thickness plane: This strain on this plane of the section of the ventral and the dosal part was larger than the strain of the plane of the central part. The strains of length direction (ε_x) on these planes in the ventral part and the dosal part were less than the strains in thickness direction (ε_z) on the same planes. The strains in both directionss of length and thickness, at the basal side on the plane of central part were lager than the strains at the apical side.
The shrinckage strain on the width-thickness planes: The strains in thickness direction (ε_z) on the basal side were lager than the strain on the apical side on this planes, and this tendency was simular to the one on the length-thickness planes. The strains of width direction (ε_y) on the central section were lager than the strains on the other sections.