Isolation and identification of the causative factors responsible for color fixation in rice bran oil

To understand the chemical nature of the dark coloring constituents responsible for color fixation in rice bran oil, crude and dewaxed rice bran oils of 6.8% free fatty acids were fractionated on a silica gel column to get a dark-colored material (0.57% of the oil). Thin-layer chromatographic analysis of the material showed a spot corresponding to monoglycerides, but there were no spots corresponding to other glycerides. It contained traces of phosphorus (<0.1 ppm, which is equivalent to 2.5 ppm phospholipids) and iron (1.3 ppm) that could not be attributed to phospholipids or to any iron-complex. Upon saponification it yielded 12% nonsaponifiable matter. Gas-liquid chromatographic analysis of the saponifiable matter (after acidification and methylation of fatty acids) showed the presence of palamitic, oleic and linoleic acids. Further, on the basis of comparison with spectroscopic data of synthetic monoglyceride, the constituent was characterized to be a mixture of monoglycerides with side chains of oxidized unsaturated fatty acids.     

Nitrogen behavior in tropical wetland rice soils. 2. The efficiency of fertilizer nitrogen,priming effect and A-values

Results of tracer pot experiments show that in tropical wetland rice soils, rice plants recovered 50–69% of applied fertilizer N in the first cropping, 7–12% in the second cropping and 1–4% in the third cropping. Recovery of fertilizer N in the presence of incorporated rice straw was decreased to 45–53% (first cropping), 9–12% (second cropping), and 3–5% (third cropping), respectively. Application of fertilizer N resulted in the increase in plant uptake of native soil nitrogen due to priming effect which valued 3–29% of total N uptake by the rice plants. A-values calculated show overestimated amounts of available soil N in relation to plant uptake of native soil N. Perhaps their use in assessing fertilizer requirement in tropical wetland rice soils would be of limited meaning.