Solubility study of shea oil and its compound classes in supercritical carbon dioxide with dynamic low flow supercritical fluid extraction

Abstract

Introduction:
Extractability of shea oil depends on its solubility and so the feasibility of upscaling the extraction method for industrial purposes can be understood by studying sample solubility.
Background:
Supercritical fluid extraction (SFE) is a greener technique than the current hexane extraction method but has not been utilized in shea oil yet and its solubility in supercritical carbon dioxide (sc-CO2) is unknown.
Aims:
This work aims to answer the following research questions:
-How does equilibrium attainment vary with flow rate for shea oil in press cake and as crude?
-How does oil solubility shift in different sample matrix and when modifying sc-CO2 properties?
-How much does solubility of the oil compound classes depend on shifts in sc-CO2 properties?
Methods:
Crude shea oil and shea press cake were subjected to SFE in dynamic mode followed by gravimetric determination. A Central Composite Face Centered (CCF) Design of Experiment (DoE) at varying sc-CO2 density and temperature was performed, and the crude shea extracts were analyzed with supercritical fluid chromatography (SFC) coupled to a charged aerosol detector (CAD) and a trapped ion mobility spectrometer/quadrupole/time of flight mass spectrometer (TIMS/TOF).
Results:
Equilibrium was established at lower flow rates for shea press cake than for crude shea. Solubility increased with sc-CO2 density and temperature for both sample but press cake yielded higher values under all conditions. SFC/CAD/TIMS/TOF identified some of the expected tri, di, mono-acylglycerides (TG,DG,MG) but couldn’t reliably identify the common free fatty acids (FFA). Finally, it was indicated that the solubility of TG was favored by higher density, DG and MG were unaffected while for FFA it was reduced.
Conclusion:
Matrix interference restricted equilibrium establishment at low flow rates while simultaneously facilitating mass transfer increasing the obtained solubility. So did, elevated density and temperature of sc-CO2. Finally, it was implied that elevated density, facilitates solubility increase as polarity of oil’s compound classes decreased.

Popular Abstract

Shea oil is derived from the seeds of the shea tree, it is rich in useful fats in confectionery industry, and it includes vitamin E which is utilized in cosmetics and pharmaceuticals. Industrially, it is extracted with hexane, a toxic and flammable solvent, exposing the operators to severe danger. Supercritical fluid extraction (SFE) is a technique that utilizes supercritical carbon dioxide (sc-CO2), a good alternative to hexane because it dissolves the same lipids but is non-toxic and abundant in the atmosphere. Carbon dioxide becomes supercritical when heated and pressurized. Altering these parameters, allows to modify sc-CO2 density. Solubility is measured when equilibrium conditions exist, in which case partitioning of analytes in the solvent is constant and maximum. The aim of this study was to develop a low flow SFE method for solubility determination of shea oil and its components in sc-CO2. Equilibrium and solubility was determined by applying SFE at multiple sc-CO2 low flow rates in crude shea oil and shea press cake. The solubilized amounts were collected and weighed. At equilibrium conditions a series of experiments were performed with sc-CO2 having different density and temperature. The collected extracts were analyzed with supercritical fluid chromatography (SFC) coupled to a high-resolution mass spectrometer (HRMS) and a charged aerosol detector (CAD). These analytical techniques led to separation of the oil’s ingredients according to their chemical class and polarity. These peaks were detected by CAD, and their area corresponded to each class concentration while their structure was identified in HRMS by their mass. Equilibrium was established at lower flows for shea press cake than for crude and also higher solubility was yielded. Furthermore, elevated sc-CO2 density and temperature increased the solubility of both samples. The SFC/CAD/HRMS method identified some of the expected fats but not all of them. The concentration trend showed that at higher density, solubility increased for some fats while decreased for others. From these results, it was concluded that proper flow was critical for equilibrium establishment and solubility determination. Press cake affected positively solubility of shea oil because of wider oil distribution in it but required strictly low flows for equilibrium. Elevated density and temperature of sc-CO2 facilitated oil solubility as a mixture and its classes separately, with possibly the non-polar classes being favored more than the polar ones.

• author: Synefakis, Evangelos
• supervisor: Azemina Bajramova
• organization: Department of Chemistry
• course: KEMR30 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Analytical Chemistry, Solubility, Shea oil, Supercritical fluid chromatography, Supercritical fluid extraction, TIMS/TOF.
• language: English
• id: 9243166
• date added to LUP: 2026-06-24 09:29:21
• date last changed: 2026-06-24 09:29:21