米の粒質に関する研究 : 第3報 米の搗減りに関する作物学的研究

抄録

With the purpose of making clear the factors concerned in milling-loss of hulled brown rice, laboratry milling-test was conducted on 80 samples of 36 varieties. Checked grains, opapue grains and the other abnormal grains were exluded from each sample prior to milling to obtain the reasonable and fundamental data on normal grains, for these abnormal grains have complicated effects upon milling-loss according to the degree of imperfection. Milling-loss was discussed in conformity to the following designation; Usual milling loss(%)=(1-Weight of white rice after milling/Weight of brown rice before milling)×100 Pure milling-loss (%)=(1 Mean weight of white rice of perfect shape/Mean weight of brown rice)×100 Therefore, usual milling-loss=Pure milling-loss+Crushing-loss Pure milling-loss(%)=Milling-loss of endosperm+Milling-loss of embryo Mean weight of embryo Milling-loss of embryo (%)≒weight of embryo/Maen weight of brown rice×100 Because, almost all embryos fall off by usual milling. 1. Relation between percentage of embryo to grain in weight and pure milling-loss. The ratio of embryo to grain in weight is varied by environment as well as by variety, and increases under high temperature during ripening and the other unfavourable environment for grain growth. The percentage of embryo to grain in weight forms itself a part of milling-loss as above mentioned, therefore, fairly high correlation (r=+0.888) was recognized between the percentage of embryo to grain and pure milling-loss. (fag. 1) 2. The milling-loss of endosperm is supporsed to be affected by thickness of bran and depth of groove (crease) on kernel. Thickness of bran on dorsal side and on lateral side and depth of the deepest groove on grain were measured, then the measurements were indicated as the ratios to √^3(grain weight.) drain weigh. Correlation coefficient between thickness of dorsal bran and milling-loss of endosperm and that between thickness of lateral bran and milling-loss of endosperm were 0.475 and 0.481 respectively, consequently, it is supporsed that more important and basic factror will concern to milling-loss of endosperm. (fig. 2, 3) Any significant correlation could not be recognized between depth of groove and milling-loss of endosperm. (fig. 4) 3. Relation between percentage of basal-white grains to normal grains and milling-loss of endosperm. Percentage of basal-white grains to normal grains (basal-white grains are included in normal grains.) in number (x) indicates the grade of insufficiency of starch accumulation into grain and high number of this percentage shows low density of starch in cells especially in peripheral region of basal portion of grain, and low density of starch in cell shows softness of cell. Correlation between log and milling-loss of endosperm was very high (+0.922) as shown in fig. 5, therfore, it is pointed out that soft starch cells in peripheral region are easily pared off by milling and milling-loss of endosperm depends mainly on the amount of soft starch cells pared off by milling. (fig. 6) 4. Relation between percentage of basal-white grains to normal grains in number (x) and pure milling-loss is composed of milling-loss of endosperm and milling-loss of embryo. Milling-loss of embryo is nearly equal to the percentage of embryo to grain in weight, and the percentage of embryo to grain has fairly high correlation (+0.702) between log x (fig. 7), and milling-loss of endosperm is also closely correlated with log x, consequently, high correlation (+0.851) is recognized between log x and pure milling-loss. (fig. 8) 5. Relation between pure milling-loss and usual milling-loss. The grains which have more numerous soft starch cells in peripheral region have higher pure milling-loss and at the same time, some of them are crushed more easily by milling on basal portion of them, then they have higher usual milling-loss. Accordingly, high correlation (+0. [the rest omitted]