Application of Fourier Transform Infrared Spectroscopy in Quantitation of Trierucin in High-Erucic-Acid Rapeseed Oils

Development of varieties of high-erucic-acid (HEAR) rapeseed with high levels of erucic acid (C22:1) would be valuable for use in oleochemical feedstocks. As an aid to this breeding effort, a rapid method to detect trierucin (C22:1 triacylglycerol), an indicator that erucic acid is being incorporated in all three positions of the triacylglycerol, would be useful. Fingerprint (1850-600 cm-1) Fourier transform infrared (FT-IR) spectra of HEAR oil extracted from Brassica napus L. cv. Mercury, trierucin, and varying amounts of trierucin spiked in this oil were recorded. The regions of 1790-1690 cm-1 and 1485-990 cm-1 were subjected to a partial least-squares (PLS) procedure to obtain a calibration equation [R2 = 0.992 and root-mean-squared deviation (RMSD) = 2.78]. The established calibration was then tested on the spectra of mixtures of another HEAR oil from B. napus cv. Turret and trierucin. The predicted values differ from the actual values with an RMSD of 1.6%. The calibration was also tested on high-erucic-acid oils from crambe (Crambe abyssinica) and nasturtium (Tropaeolum majus L.) seeds. For crambe, the value found (0.4%) was close to that reported in the literature, while the value of 75% for nasturtium oil was close to the value for total triacylglycerols with erucic acid in the 2-position as reported in the literature. FT-IR spectra of triolein (C18: 1 triacylglycerol), trieicosenoin (C20:1 triacylglycerol), and trinervonin (C24:1 triacylglycerol) compared with the FT-IR spectrum of trierucin revealed the uniqueness of IR spectrum of trierucin that forms the basis of PLS analysis of trierucin in HEAR oils.