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.
