ISOLATION AND IDENTIFICATION OF THE CAUSATIVE FACTORS RESPONSIBLE FORCOLOR FIXATION IN RICE BRAN OIL

To understand the chemical nature of the dark coloring constituents re sponsible 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 c olumn to get a dark-colored material (0.57% of the oil). Thin-layer ch romatographic analysis of the material showed a spot corresponding to monoglycerides, but there were no spots corresponding to other glyceri des. 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 attribu ted to phospholipids or to any iron-complex. Upon saponification it yi elded 12% nonsaponifiable matter. Gas-liquid chromatographic analysis of the saponifiable matter (after acidification and methylation of fat ty acids) showed the presence Of palamitic, oleic and linoleic acids. Further, on the basis of comparison with spectroseopic data of synthet ic monoglyceride, the constituent was characterized to be a mixture of monoglycerides with side chains of oxidized unsaturated fatty acids.