Rapid FTIR determination of water, phenolics and antioxidant activity of olive oil

Abstract

A rapid Fourier transformed infrared (FTIR) attenuated total reflectance (ATR) spectroscopic method was applied to the determination of water content (WC), total phenol amount (TP) and antioxidant activity (ABTS.p) of virgin olive oils (VOO) and olive oils. Calibration models were constructed using partial least squares regression. Oil samples with WC ranging from 289 to 1402 mg water/kg oil, with TP from 46 to 877 mg gallic acid/kg oil and with ABTS .+ from 0 to 5.7 mmol Trolox/kg oil were considered for chemometric analysis. Better results were obtained when selecting suitable spectral ranges; in particular, from 2260 to 1008 cm 1 for WC, from 3610 to 816 cm 1 for TP and from 3707 to 1105 cm 1 for ABTS.p. Satisfactory LOD values by the FTIR-chemometric methods were achieved: 9.4 (mg/kg oil) forWC; 12.5 (mg gallic acid/kg oil) for TP, and 0.76 (mmol Trolox/kg oil) for ABTS .+ The evaluation of the applicability of these analytical approaches was tested by use of validation sample sets (n = 16 forWC, n = 11 for TP and n = 14 for ABTS) with nearly quantitative recovery rates (99-114%). The FTIR-ATR method provided results that were comparable to conventional procedures. Practical applications: The presented method is based on ATR-FTIR in combination with multivariate calibration methodologies and permits a simultaneous evaluation of important quality parameters of VOO (WC, TP and ABTS.p). This approach represents an easy and convenient means for monitoring olive oil quality with the advantage of ease of operation, speed, no sample pretreatment and no consumption of solvents. The data obtained with this method are comparable to those obtained using the official reference method. Therefore, the technique is highly plausible as an alternative to the standard procedure for routine analysis or control at-line of production processes.