The composition of lipids from rice hulls and from the surface of rice caryopsis

Samples of hulls, of whole and ground caryopsis and of bran obtained from the Brazilian rice variety IAC 1246, were extracted with hexane and the characteristics and composition of the corresponding lipids were determined. The lipids from rice hulls showed a four times higher content of unsaponifiable matter and of free fatty acids than those from rice bran and rice caryopsis. There were also differences in the fatty acid composition as evidenced by the presence of 2–3% of saturated C₂₂ and C₂₄ acids and a lower proportion of unsaturated acids in the rice hull lipids. On the other hand there was a close resemblance between the rice hull lipids and those on the surface of the caryopsis. Chromatographic analysis of the unsaponifiable matter of lipids from rice hulls and caryopsis surface disclosed the presence of hydrocarbons, alcohols and sterols in ascending order, the sterols consisting of about 50% of β-sitosterol, 20–40% of campesterol, 10–20% of stigmasterol and 2–3% of cholesterol. On the basis of the above results it was concluded that a preliminary solvent extraction of paddy rice in order to remove the waxy lipids from the hulls and the caryopsis surface would benefit the subsequent milling process and improve the quality of the brown rice and of crude rice bran oil.