A facile NMR method for the quantification of total, free and esterified sterols in virgin olive oil

This study describes a simple analytical technique based on NMR spectroscopy for the determination of free and esterified sterols in olive oil. Free sterols were determined by 31P NMR upon derivatization of free sterols with a phosphorous reagent, whereas total (free + esterified) sterols were obtained from 1H NMR. The present NMR method was validated by performing a comparison study with the reference method of gas chromatography. The agreement between NMR and GC methods was evaluated by using the Bland and Altman statistical analysis. The distribution of the data points in the bias plot showed that ∼96% of the measurements of total, free and esterified sterols in 24 extra virgin olive oil samples from various regions of Greece were within the limits of agreement of the two methods.