Quantitative determination of free fatty acids in extra virgin olive oils by multivariate methods and Fourier transform infrared spectroscopy considering different absorption modes

Figures & data

Figure 1. The average Fourier transform infrared spectroscopy spectra of 10 extra virgin olive oil samples in (a) reflection and (b) transmission modes in view of the full scale.

Figure 2. Normal Fourier transform infrared spectroscopy spectra of the 15 calibration standards in the one of selected spectral regions between 1724 and 1646 cm⁻¹ in the transmission mode.

Figure 3. First derivative Fourier transform infrared spectroscopy spectra of the 15 calibration standards in one of the selected spectral regions between 1724 and 1646 cm⁻¹ in the transmission mode.

Figure 4. The best partial least squares calibration model for the determination of free fatty acids in extra virgin olive oils by Fourier transform infrared spectroscopy.

Table 1. Equation values of the developed partial least squares calibration models for the determination of free fatty acids in extra virgin olive oils using Fourier transform infrared spectroscopy.

Absorption Mode	Region Type	Range, cm^−Citation1	R2	RMSEC	RMSECV	Factors
Reflection	Normal	1724–1646	0.99034	0.0298	0.0450	3
		3324–3023	0.94075	0.0729	0.1830	2
		1724–1646 + 3324–3023	0.98211	0.0405	0.0677	3
	First Derivative	1724–1646	0.97565	0.0472	0.0674	2
		3324–3023	0.74103	0.1440	0.1910	1
		1724–1646 + 3324–3023	0.98789	0.0334	0.0817	3
Transmission	Normal	1724–1646	0.99862	0.0113	0.0156	3
		3324–3023	0.99957	0.00632	0.0134	5
		1724–1646 + 3324–3023	0.99979	0.00441	0.0107	7
	First Derivative	1724–1646	0.99896	0.00980	0.0147	4
		3324–3023	0.99649	0.0180	0.0207	1
		1724–1646 + 3324–3023	0.99867	0.0111	0.0145	2

R²: coefficient of determination; RMSEC: root mean square error of calibration; RMSECV: root mean square error of cross-validation.

Table 2. Results of triplicate analysis of free fatty acids in extra virgin olive oils by American Oil Chemists’ Society and the proposed transmission-based Fourier transform infrared spectroscopy methods.

EVOO Samples	AOCS-1	AOCS-2	AOCS-3	Mean	SD	FTIR-1	FTIR-2	FTIR-3	Mean	SD
EVOO1	0.20	0.22	0.18	0.21	0.02	0.22	0.22	0.23	0.22	0.02
EVOO2	0.20	0.20	0.21	0.20	0.01	0.19	0.20	0.20	0.20	0.01
EVOO3	0.26	0.28	0.27	0.27	0.01	0.28	0.27	0.28	0.28	0.01
EVOO4	0.54	0.49	0.50	0.50	0.03	0.49	0.49	0.49	0.49	0.00
EVOO5	0.97	0.99	0.99	0.98	0.01	0.98	0.98	0.99	0.98	0.01
EVOO6	0.42	0.41	0.41	0.41	0.01	0.39	0.40	0.40	0.40	0.01
EVOO7	0.79	0.80	0.80	0.80	0.01	0.80	0.80	0.80	0.80	0.00
EVOO8	0.53	0.53	0.54	0.54	0.01	0.53	0.53	0.53	0.53	0.00
EVOO9	0.91	0.90	0.90	0.90	0.01	0.91	0.90	0.90	0.90	0.01
EVOO10	0.89	0.90	0.90	0.89	0.01	0.87	0.88	0.88	0.88	0.01

Boskou, D. Olive Oil: Chemistry and Technology; 2nd ed.; AOCS Press: Champaign, IL, 2006; 113.

 Google Scholar

Di Vaio, C.; Nocerino, S.; Paduano, A.; Sacchi, R. Influence of Some Environmental Factors on Drupe Maturation and Olive Oil Composition. Journal of the Science of Food and Agriculture 2013, 93, 1134–1139.

 PubMed Web of Science ®Google Scholar