Rice bran oil (RBO) contains significant amounts of the natural antioxidants γ-oryzanol and tocopherols, which are lost to a large degree during oil refining. This results in a number of industrial residues with high contents of these phytochemicals. With the aim of supporting the development of profitable industrial procedures for γ-oryzanol and tocopherol recovery, the contents of these phytochemicals in all the residues produced during RBO refining were evaluated. The samples included residues from the degumming, soap precipitation, bleaching earth filtering, dewaxing and deodorisation distillation steps. The highest phytochemical concentrations were found in the precipitated soap for γ-oryzanol (14.2 mg g(-1), representing 95.3% of total γ-oryzanol in crude RBO), and in the deodorisation distillate for tocopherols (576 mg 100 g(-1), representing 6.7% of total tocopherols in crude RBO). Therefore, among the residues of RBO processing, the deodorisation distillate was the best source of tocopherols. As the soap is further processed for the recovery of fatty acids, samples taken from every step of this secondary process, including hydrosoluble fraction, hydrolysed soap, distillation residue and purified fatty acid fraction, were also analyzed. The distillation residue left after fatty acid recovery from soap was found to be the best source of γ-oryzanol (43.1 mg g(-1), representing 11.5% of total γ-oryzanol in crude RBO).

The stability of α-, (β+γ)- and δ-tocopherols present in rice bran oil at different heating temperatures has been evaluated. For this purpose, samples of rice bran oil from chemical and physical refining processes in Brazilian industries were studied. The oils were submitted to cabinet drying without air circulation in the absence of light at 100 ºC, 140 ºC and 180 ºC. The samples were taken before heating and after 48, 144, 240, 336, 432, 576, 768, 1008 and 1368h of heating. The analyses of tocopherols were made by high performance liquid chromatography, with a fluorescence detector. It was determined that α-tocopherol was the compound with the fastest degradation rate at the three heating temperatures. The highest degradation rate of tocopherols in both oils occurred at 180 ºC. Among the tocopherols studied, α tocopherol presented the lowest stability, followed by (β+γ)- and δ-tocopherols.

BACKGROUND: Rice bran oil is unique among edible oils owing to its rich source of commercially and nutritionally important phytochemicals, such as oryzanol. γ-Oryzanol performs an important role in the stability of rice bran oil. The crude rice bran oil obtained by solvent extraction is subjected to either chemical or physical refining to meet the specifications of edible-grade vegetable oil. These refining processes can cause the compounds present in rice bran oil to degrade. The aim of this study was to evaluate the stability of γ-oryzanol present in chemically and physically refined rice bran oils, when submitted to temperatures of 100, 140, and 180°C for a period of 1368 h. RESULTS:The chemically refined rice bran oil presented a lower γ-oryzanol content than the physically refined rice bran oil at all heating temperatures. The losses of γ-oryzanol at 100°C, 140°C, and 180°C at the end of the heating periods for the chemically refined oil were 53.47%, 58.48%, and 97.05% respectively, and for the physically refined oil the losses were 38.11%, 53.58%, and 91.11% respectively. CONCLUSION: Based on the results of the time to reduce the oryzanol concentration by 50% and 100%, it is observed that the oil of rice meal refined physically presents greater stability, in the different temperatures studied and over time, than the oil of rice meal refined chemically. Thus, for situations where the oil needs to be subjected to prolonged heating, a temperature of 100°C is indicated. In this condition, the physically refined oil is better for maintaining a higher concentration of γ-oryzanol.

SummaryThe aim of this work was to develop an extraction method to recover γ‐oryzanol and tocopherols from the distillation residue of the fatty acids generated during the neutralisation step of the rice bran oil refining process. The phytochemicals extraction was performed with different solvents (chloroform, methanol, methyl ethyl ketone and acetone) at a ratio of 10:1 v/w (solvent: sample), by agitating the mixture for 10 min at room temperature (20 °C ± 2 °C), then stored at −18 °C for 15 h. The γ‐oryzanol and tocopherol content in the extracted fractions were concentrated and quantified using reverse phase high‐performance liquid chromatography coupled with UV–vis and fluorescence detector, respectively. It was observed that only one step of extraction with methanol resulted in an increased concentration of tocopherols for about six times, with a recovery of 51.50%. However, using two stages of extraction, the mixture of methanol and methyl ethyl ketone (1:1, v/v) allowed the recovery of 92.15% of tocopherols and 84.12% of γ‐oryzanol, increasing the initial concentration of these phytochemicals in about three times. These results show that there is a great possibility of these phytochemicals recovery from the distillation residue from fatty acid recovery.

No abstract