On Moisture Content of Rice : 2. Moisture content with reference to the methods for measuring moisture content in relation to the grain texture of rice.

Abstract

To examine the factors in different moisture content of rice according to rice grain texture, the studies were undertaken to clarify the relationship between the moisture content measured by the several drying methods at different temperatures and the grain texture of several varieties. The results are summarized as follows. 1. Globe of fat, crystal of protein and a part of starch granule contained in hulled rice were collapsed owing to the drying at temperature of (hereinafter referred to as I05°C drying), and it was recognized that the marginal tissue of rice grain containing fat and protein was scorched by the drying, and that the components came to be collapsed by the I35°C drying, and at that high temperature the scorch of the marginal tisste of endosperm was also recognized. But, it was recognized that these were not collapsed or scorched when dried by the vacuum oven method (referred to as O. : 1/1000 mmHg, 97±2°C). Therefore, if the moisture content of rice when dried at lower temperature than that by V. O. D is regarded as free moisture the moisture content of rice by the V. O. D could be regarded as free moisture content, and the difference between the moisture content by I35°C drying and that by V. O. D could be regarded as moisture. 2. The moisture content of hulled rice by the drying is higher than that by the V. O. D, and the moisture content of the internal polished rice (containing about 30% polished rice), is lower than that by the V. O. D. Therefore, it is recognized that under drying condition the bound moisture is contained in the moisture content of hulled rice. So that, all free moisture content must be measured under the V. O. D condition. 3. Generelly, atmospheric humidity has direct effect upon the moisture content by 70°C drying, but not affect on free or bound moisture content under the drying condition at higher temperatures than 70°C. 4. The free moisture content is usually higher in starch-cell tissue, in coarser tissue, in unripened kernel and in soft verieties of rice. Than in bran tissue, in compact tissue, in fully rippened kernel and in hard varieties respectively. The bound content is usually higher in bran and aleuron layer in the marginal tissue of rice grain, than in starch-cell tissue, and higher in fully ripened rice kernel, and semi-soft varieties of rice (somewhat harder than soft varieties of rice).