On the Forms of Phosphorus Compounds in Rice Kernels of Some Varieties with Different Degrees of Palatability

Abstract

Rice grains of four varieties harvested at 11 days, 25 days, 35 days after flowering and stored at - 20°C, and those harvested at 35 days and stored for 120 days at room temperature were used for the analysis of phosphorus compounds in milled rice, rice bran and embryo. The results obtained are summarized as follows. 1. In brown rice and milled rice of palatable varieties, the amount of inorganic phosphorus was higher than that of less palatable varieties harvested at the middle stage of ripening when starch was rapidly accumulated, but was lower at the later stage when the accumulation of starch had been completed. Inorganic phosphorus in bran and milled rice of every variety was severely decreased during post-harvest storage. 2. Phosphorus contents in sugar phosphates and related compounds, which were culculated by subtracting inorganic and phytic phosphorus from acidsoluble total phosphorus, increased with increasing of ripening and storing time, and was found more abundantly in rice bran than other parts of the kernels. In palatable varieties, the amounts of phosphorus in sugar phosphates and related compounds were higher in rice bran and milled rice, at the early and middle stage of ripening, while they became lower during post-harvest storage, as compared with inferior taste varieties. 3. Phytin phosphorus was increased with increasing of ripening and storing time, especially in the later ripening period. In general, phytin phosphorus was abundant in rice bran, being much higher in palatable varieties. Amount of phytin phosphorus in milled rice was also slightly higher in palatable varieties than the less palatable varieties, at the later stage of ripening. 4. The amount of nucleic acid phosphorus was much higher at an early stage of maturity and decreased with increasing of matueity or of time of post-harvest storage. Nucleic acid phosphorus content in milled rice of palatable varieties was low, being especially low at the early stage of ripening. However, in embryo, it was preserved high during post-harvest storage, in higher level in the inferier taste varieties. 5. With the lapse of time after flowerling or harvest, the amount of phosphatide phosphorus was increased in brown rice and markedly in milled rice at the later stage of ripening. Higher amount of phosphatide phosphorus was found in milled rice of palatable varieties at the middle and later stage of maturity, suggesting that phosphate content moved easily in these varieties. At storing period, the amounts of phosphatide phosphorus were high in embryo, rice bran and milled rice in order. 6. The amount of starch and protein phosphorus was small and did not increase with maturity, indicating that much of the excess phosphorus was not bound to the starch. In the palatable varieties, the amounts of starch and protein phosphorus were small in milled rice at the middle stage of ripening and it is probable that this small amount might be due to the low content of protein in milled rice of these varieties.