One-step rapid extraction of phytosterols from vegetable oils

The conditions for the extraction of phytosterols (campesterol, stigmasterol and β-sitosterol) from vegetal oils were optimized by means of response surface methodology (RSM). A 2⁴ central composite rotatable design (CCRD) was used to investigate the effects of four independent variables: sample weight (g), saponification temperature (°C), saponification time (h) and number of extractions (n). The CCRD was carried out in 27 trials, including eight axial and three central points; and the response variables were the contents of campesterol, stigmasterol, β-sitosterol and total phytosterols. The optimized conditions established by the RSM were 0.3 g of sample, saponification for 3 h at 50 °C and 4 extractions with n-hexane. Satisfactory values for linearity, recovery, repeatability, accuracy, precision, limits of detection (2.0-2.3 mg/100 g) and quantification (6.5-7.7 mg/100 g) were achieved. The optimized method was also validated by comparison with the official AOCS method, and the contents of stigmasterol and β-sitosterol did not show significant differences (p > 0.05) when determined by both methods. However, low values (p < 0.05) for campesterol were found when the samples were analyzed by the AOCS method. The method optimized and validated in the present work is easy to carry out, fast and accurate. The method was successfully applied to sunflower, canola, corn, soybean and olive oils, and the lowest contents of total phytosterols were found in olive oil while and the highest amounts, in corn oil.