Comparative study on the stability of crude and refined rice bran oil during long-term storage at room temperature

The effect of the full refining process on the stability of rice bran oil during storage at room temperature was studied. Crude and refined rice bran oil were kept in the dark and were exposed to light for 240 days, and every 10 days samples were drawn and analysed. The storage stability of crude and fully refined rice bran oil was determined and compared with respect to fatty acid composition, tocopherols, tocotrienols, sterols and -y-oryzanol content. In addition, the oxidative status was evaluated by determining the concentration of polar compounds and the oil stability index (OSI). A good correlation between the decrease of total tocopherols and the OSI was found. alpha-Tocopherol had the highest correlation coefficient (r(2) = 0.9653) in crude rice bran oil kept in the dark, and, alpha-tocopherol showed the lowest in the refined sample (r(2) = 0.4722). The order of stability of tocopherols and tocotrienols in crude oil was completely different from that in refined oil. In comparison to tocopherols, sterols showed a better stability during the entire storage period. The exposure to daylight heavily affected the composition and the stability of both crude and refined rice bran oil.