Extraction of phytosterols and tocopherols from rapeseed oil waste by supercritical CO2 plus co-solvent: A comparison with conventional solvent extraction

Abstract

In the present study, modified extraction methods using supercritical CO₂ were investigated in order to obtain high-added value compounds from rapeseed oil deodorizer distillate and comparisons were done with modified Soxhlet extraction (solvent extraction + silica). For supercritical fluid extraction (SFE), the optimal extraction parameters were temperature of 40 °C, pressure of 350 bar (for phytosterols), 400 bar (for tocopherol), 5 wt% ethanol as co-solvent, and saponification pretreatment. The optimized SFE procedure led to the recovery of three main phytosterols (50 wt % β-sitosterol, 23.91 wt % Brassicasterol, and 36.25 wt % Campesterol) and only α-tocopherol. Moreover, there was no synergistic effect with saponification pretreatment + co-solvent and the efficiency and concentration of target compounds were less than supercritical CO₂ + co-solvent. Also, comparative Data showed that the efficiency of phytosterols and tocopherols was approximately three times higher (p < 0.05) in SFE relative to modified Soxhlet extraction. Furthermore, the use of ethanol (5 wt %) as co-solvent, improved phytosterols and tocopherol efficiency and purity. The SFE technique offers various advantages over the modified Soxhlet extraction technique, including increasing the solubility of tocopherols and sterols by using CO₂+ co-solvent, minimized usage of toxic organic solvents and increased purity of extracted products.

Keywords: Food science; Food technology; Solvent extraction; Sterols; Supercritical fluid extraction; Tocopherol.

Figure 1

Schematic flow diagram of the SFE modular system: (C) cooler; (D) temperature equilibration coil; (E) extraction vessel; (H) oven; (S₁, S₂) sample collection vessel; (F) volumetric flow meter; (M) manometer; (T) thermometer.

Figure 2

Supercritical fluid extraction of a,b) phytosterols and c,d) tocopherols using different compositions of ethanol co-solvent. Experimental conditions: 60 min extraction at 40 °C; 5 mL/min CO₂ flow. (CO₂- E: CO₂ without ethanol, E: ethanol).

Figure 3

Efficiency (Y) and percentage (C) of a) sterols and b) tocopherols extracted from the saponified rapeseed oil deodorizer distillate with 5% (wt.%) ethanol as co-solvent over 1 h at 40 °C and 5 mL/min CO₂ flow. (The drawn bars on each point in the linear graph represent the standard deviation).

Figure 4

GC-MS chromatogram of extracted A) phytosterols and B) tocopherols using SFE with mixed fluid (95% CO₂ and 5% ethanol; 40 °C; and 350–400 bar); C) GC-MS chromatogram of extracted rapeseed by-product after modified soxhlet extraction at 60 °C.