Isolation and identificatin of the causative factors responsible for colour 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 darkcolored
material (0.57% of the oil). Thin-layer chromat~
graphic 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 chromat~
graphic analysis of the sapouifiable 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.