REFINING OF HIGH FREE FATTY ACID RICE BRAN OIL AND ITS QUALITY CHARACTERISTICS

ABSTRACT

Commercial rice bran contains 15–20% of oil and also an endogenous lipase which degrades the oil and produces free fatty acids (FFAs). This study was undertaken to examine the quality of refined oil prepared from crude oil after the action of endogenous lipase in bran. The oil which was degraded by lipase to low, medium and high FFAs, upon extraction in the rice bran oil industry were obtained and were refined in the laboratory, and quality of the oils was studied. The crude oils had FFA of 6.5, 36.0 and 87.0%; oryzanol content of 1.52, 1.55 and 1.65%; color of 32.0, 65.0 and 65.0, lovibond units; unsaponifiable matter of 3.2, 4.2 and 4.9%; phytosterol content of 4,600, 4,000 and 1,900 ppm; and sum of tocopherols and tocotrienols of 962, 56 and 96 ppm, respectively. After refining these three crude oils (6.5, 36.0 and 87.0% FFA) were refined; the resultant oils had an FFA content of 0.4, 2.4 and 4.8%; oryzanol content of 1.13, 2.5 and 6.35%; color of 20.0, 55.0 and 50.0 lovibond units; unsaponifiable matter of 3.5, 6.5 and 33.4%, phytosterol content of 4,900, 6,100 and 13,800 ppm, and the sum of tocopherols and tocotrienols of 1,050, 880 and 740 ppm, respectively. The refined oils produced from high FFA crude oil had high amounts of unsaponifiable matter, oryzanol, phytosterols and sum of tocopherols and tocotrienols than the permitted level for refined rice bran oil. The refined rice bran oil obtained from fresh rice bran (without lipase action) contained about 90% of triacylglycerols whereas, the refined oil from that of high FFA bran oil showed about 10% triacylglycerols. Hence the latter cannot be used as an edible oil, but instead can be used at low levels as a nutraceutical in foods.

PRACTICAL APPICATIONS

The suitability of refined rice bran oils from crude oils obtained from lipase-acted brans for use as edible oil was investigated. For this purpose, the lipase-acted bran oils were subjected to physicochemical analysis along with their refined oils. The refined oils had high amounts of phytosterols as well as tocopherols and tocotrienols when compared with their respective crude oils. Fatty acid and triacylglycerol composition of the refined oils prepared from low free fatty acid (FFA) crude oil or the high FFA crude oil were almost similar with little changes. As the refined oils obtained from high FFA crude oils had very low levels of triacylglycerols and a high unsaponifiable matter, it cannot be used as refined rice bran oil. However, it can be used as a nutraceutical of rice bran oil in small amounts to provide health benefits.