Quantitative determination of olive oil adulteration with cheap oils using ATR-FTIR spectroscopy

Extra virgin olive oil (EVOO0) is renowned for its nutritional benefits, quality and flavor, which contribute to its higher market value and make it susceptible to adulteration with cheaper vegetable oils like corn, sunflower, and soybean. This study utilized Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy as a rapid, cost effective, and direct technique to assess the purity of olive oil samples by measuring their absorbance across the 5000-500 cm^-1 wavenumber range. Fifty fresh EVOO samples from Palestinian farmers in the West Bank were analyzed, with one sample blended with varying proportions of other vegetable oils to create calibration curves for quantifying adulteration levels. The method identified specific absorbance ratios at certain wavenumbers characteristic of pure EVOO; for instance, the ratio at 583.9/2922.2 cm^-1 remained consistent across all samples, averaging 0.1136 ± 0.0012. Equations were derived to quantify the extent of adulteration, such as: wt% corn oil = -779.92 R + 776.71 (R² = 0.997, P = 1.6E-11), where R is the absorbance ratio at 2853.6/1160.6 cm^-1; wt% sunflower oil = 567.31 R - 610.16 (R² = 0.997, P = 2.1E-11), with R at 722.3/1463.2 cm^-1; and wt% soybean oil = 1641.8 R - 576.64 (R² = 0.998, P = 2.0E-11), with R at 1232.0/2922.2 cm^-1. The method has been validated and results showed that this method for determination of adulated oil is accurate, precise, linear and selective. These findings underscore the efficacy of ATR-FTIR spectroscopy as a reliable tool for detecting and quantifying the adulteration of EVOO with cheap oils.