Antioxidant Activity of a Oryzanols Concentrate by Differential Scanning Calorimetry

Oryzanols are natural antioxidants that are found in appreciable amounts in rice bran oil. However, by chemically refining the crude rice bran oil they are lost during the chemical neutralization step leaving the oil refined with very little oryzanols. The chemical neutralization leaves a residue called "soapstocks" where most of these antioxidants are found. From the soapstocks and by relatively simple procedures it is possible to obtain a oryzanols concentrate which may contain 33% of them. However, its antioxidant power has been little studied in oils compared to other natural antioxidants. Therefore, the present work gives information about the antioxidant power of a concentrate of oryzanols compared to natural antioxidants such as tocopherol and synthetic antioxidants such as butylhydroxytoluene (BHT) added in oils with different degrees of unsaturation and without antioxidants. The results determined by the differential scanning calorimetry method show that the antioxidant power was variable according to the method used. The tocopherol protected the oils from the oxidation at 130°C (soybean and high oleic sunflower) better than the oryzanols concentrate by the isothermal method. When the non-isothermal method was used it was found that the-tocopherol protected soybean oil better than oleic high sunflower oil compared to the oryzanols concentrate. However, when comparing BHT with oryzanols concentrate, BHT generally had a lower protection in both oils and both methods. These results show that the oryzanols concentrate has a protective effect of the oxidation of the studied oils, however, this could depend on the degree of the oil unsaturation.