Quantitative Detection of Virgin Olive Oil Adulteration With Olive-Derived Oils by Near- and Mid-Infrared Spectroscopy

Abstract

The main purpose of this study was to quantify adulteration of virgin olive oil (VOO) with lower priced olive-derived oils, namely, olive pomace oil (OPO) and refined olive oil–virgin olive oil blends (ROO), using infrared (IR) spectroscopy combined with chemometrics. Five samples from each group (VOO, OPO, and ROO) were purchased and analyzed for common physicochemical parameters, including free fatty acids, peroxide value, conjugated dienes/trienes, chlorophylls, and carotenoids. Significant differences were observed among VOO, OPO, and ROO across quality attributes: VOO and OPO differed in all properties, VOO and ROO in all except K₂₃₂ values, and ROO and OPO only in conjugated dienes and carotenoids. To evaluate adulteration, equally pooled oils from each group were blended, yielding 120 OPO–VOO and 120 ROO–VOO mixtures with adulterant levels from 0.05% to 100% (w/w). Spectra were collected using benchtop FT-MIR, benchtop FT-NIR, and handheld NIR spectrometers. All developed partial least squares regression models showed high predictive performance for quantifying OPO and ROO in VOO. For OPO quantification, benchtop FT-NIR with a 6-mm transflectance accessory gave the best results (residual predictive deviation [RPD] = 28.0), followed by FT-MIR with ATR (RPD = 13.8). For ROO prediction, FT-MIR performed slightly better (RPD = 21.8) than FT-NIR (RPD = 20.4). Pathlength effects in NIR applications (1 vs. 6 mm) strongly influenced model performance, with 6 mm yielding superior outcomes. Handheld NIR, although less accurate (RPD = 5.69–8.59), still provided reliable estimates, offering rapid and on-site screening for fraud prevention in the olive oil sector.