Quality Changes and Tocopherols and γ-Orizanol Concentrations in Rice Bran Oil During the Refining Process

The quality changes and the concentrations of tocopherols and gamma-oryzanol, during successive steps of rice bran oil refining (RBO), were studied. For this purpose, samples of crude, degummed, neutralized, bleached, dewaxed and deodorized RBO were taken from an industrial plant and analyzed. The moisture, pH, acidity, peroxide value and unsaponifiable matter, were determined. The fatty acid composition was evaluated by GC, and the concentrations of tocopherols and gamma-oryzanol were determined using HPLC with fluorescence and UV-Vis detection, respectively. To identify gamma-oryzanol components, fractions of the HPLC eluant were collected and analyzed using mass spectrometry. Oil refining reduced the peroxide value and acidity to 1 and 3% of the values obtained in crude RBO, respectively. The fatty acid composition were not significantly altered during refining. The concentrations of the tocopherols in RBO followed the order alpha > (beta + gamma) > delta. The total concentration of tocopherols was 26 mg/100 g, and remained practically unaltered during refining. Up to nine components were distinguished in gamma-oryzanol. After collecting the elution fractions, up to six components were identified by electrospray mass spectrometry. Refining reduced the total concentration of gamma-oryzanol to 2% of its initial value.