Quantitative determination of fatty acid content in Sclerocarya birrea A.Rich.Hochst (Marula) seed oil using MIR calibration models

The quality control of seed oils is an important aspect to consider. Natural seed oils have received much attention as cosmetic ingredients, due to the purported folkloric benefits to the skin. Marula oil is a cold-pressed light-nutty oil included in cosmetics due to the abundance of fatty acids. The commercialisation of Marula seed oil as a natural ingredient in cosmetic products necessitates the need for quality control procedures to ensure the supply of good efficacious oil. There are currently no standards available for the quality control of Marula seed oils. Hence, the study was undertaken to provide some insight into the chemical variation and to investigate the feasibility of using mid-infrared (MIR) spectroscopy as a simple and non-destructive technique for the quantification of the major fatty acids in Marula seed oils. A comparative study was conducted using 1D and 2D chromatography as reference methods. Spectra of the oil were acquired using a Bruker^® Alpha-P MIR spectrometer. Partial least squares (PLS) regression models were developed based on MIR data. The calibration models revealed good correlation between the MIR data and 1D-GC values (R² > 0.80). The predictive ability of the models (Q² _cum) was greater than 0.50. In contrast, the correlation between 2D-GC and the MIR data was low, with R² values ranging between 0.17 and 0.30. The predictive ability of the models was low (Q² _cum < 0.50). In this study, MIR spectroscopy was identified as a good alternative quality control method, since the technique yielded promising results.