|The typical composition of crude rice
bran oil is 81.3-84.3% triglycerides, 2-3% diglycerides, 5-6% monoglycerides,
2-3% free fatty acids, 0.3% waxes, 0.8% glycolipids, 1.6% phospholipids,
4% unsaponifiables. In comparison with other vegetable oils, crude
rice bran oil tends to contain higher levels of non-triglyceride components,
most of which are removed during further refining processes. The free
fatty acids, monoglycerides and diglycerides in rice bran oil are
associated with enzymatic hydrolysis. The phospholispids predominantly
include phosphatidylcholine, phosphatidylethanaolamine, and phosphatidylinositol.
The wax content of rice bran oil can be somewhat variable, depending
upon cultivar and processing parameters. Various sterols constitute
the principal portion of the unsaponifiable fraction of nutraceutical
interest. In recent years, many studies have been conducted in the
area of utilization of these minor components as co-products of rice
bran oil processing.
Table 1 compares the fatty-acid composition of rice bran oil with
that of peanut, soybean, and cottonseed oils.
Table 1. Fatty-acid composition of selected oils.
From Young (1996), Sipos and Szuhaj (1996), and Jones and King (1996).
Data for rice bran oil are from Riceland Foods, Inc.
Oleic and linoleic fatty acids constitute more than 80% of the
fatty acids of the glycerides. Rice bran oil is similar to peanut
oil in fatty acid composition with a saturation level that is slightly
higher than that of conventional soybean oil. The much lower linolenic
acid content of rice bran oil makes it more stable to oxidation
than soy oil.
The quality characteristics of properly refined rice bran oil include
a maximum free fatty acid levels (as oleic acid) of 0.1%, a maximum
peroxide value of 1.0 meq/kg, 0.05% moisture, an iodine value of
99108, saponification value of 180-195, and a Lovibond color
value of 3.5R. Appearance of rice bran oil ranges from cloudy to
clear depending on the degree of dewaxing and winterization processes