Detection of green coffee oil adulteration using time-domain nuclear magnetic resonance relaxometry and infrared spectroscopies

Green coffee oil (GCO) is a high-value product widely used in the food, cosmetic, and pharmaceutical industries, being susceptible to adulteration with low-cost vegetable oils. This study aimed to develop rapid and non-destructive methods based on time-domain nuclear magnetic resonance (TD-NMR) relaxometry and Fourier transform infrared (FTIR) spectroscopy to detect adulteration of GCO with sunflower oil (SO). Calibration samples containing different proportions of GCO and SO (0-100%) were analyzed using low-field 1 H TD-NMR relaxometry, FTIR spectroscopy, and high-resolution 1 H NMR as a reference method. TD-NMR measurements were performed using CPMG pulse sequence, and relaxation parameters were evaluated through inverse Laplace transform (ILT) and three-exponential fitting approaches. Among the relaxation components, T 2(3) showed the highest sensitivity to compositional changes, presenting a linear correlation with GCO concentration (R 2 = 0.9839). FTIR univariate models based on the band at 1670 cm -1 , associated with unsaturation-related vibrational modes, and the band at 3008 cm -1 , attributed to cis =C–H stretching of unsaturated lipid chains, also demonstrated good performance, achieving correlation coefficients of 0.9649 and 0.8866, respectively. Commercial samples analyzed by TD-NMR and FTIR revealed spectral and relaxation profiles inconsistent with authentic GCO in two products, which was further confirmed by high-resolution 1 H NMR through the absence of cafestol and kahweol markers. The results demonstrate that TD-NMR and FTIR provide rapid, simple, and accessible screening approaches for detecting adulteration in green coffee oil, with potential applications in routine quality control and food fraud detection.