Rapid determination of phospholipid content of vegetable oils by FTIR spectroscopy combined with partial least-square regression

A rapid mid-FTIR method was developed to quantitatively determine the total phospholipid (PL) content of vegetable oils. The method simply requires that the oil be diluted 4:1 (w/w) with hexane, its spectrum taken and ratioed against a hexane background. A calibration was devised using partial least squares by adding purified soybean PL at levels of 0.02-2.0% to phospholipid-free oils (soybean, rapeseed, sunflower) using the spectral region encompassing 1357-1000 cm−1 and validated using the AOCS 12-55. Using calibration and leave-one-out cross-validation predictive errors, a 200-20,000 ppm calibration was accurate to within ±362 and 488 ppm, respectively, while for sub-calibrations ranging from 200 to 2000; 2000 to 8000 and 8000 to 20,000 ppm, they were ±72-172, ±119-220, and ± 242-371 ppm, respectively. Although limited to 3 oil types in this study, the calibration is simple to devise and can be broadened to the universe of oil types of interest, the analytical protocol being straightforward and the analysis readily automatable.