FTIR spectroscopy coupled with chemometrics of multivariate calibration and discriminant analysis for authentication of extra virgin olive oil

Figures & data

Table 1. Fatty acid composition of extra virgin olive oil (EVOO), grape seed oil (GSO), soybean oil (SO), and walnut oil (WO) using gas chromatography-flame ionization detector.

Edible oils	Fatty acid composition (% w/w)
	Palmitic acid (C16:0)		Palmitoleic acid (C16:1)		Stearic acid (C18:0)		Oleic acid (C18:1)		Linoleic acid (C18:2)		Linolenic acid (C18:3)		Arachidic acid (C20:0)
	Exp.	Ref	Exp.	Ref	Exp.	Ref	Exp.	Ref	Exp.	Ref	Exp.	Ref	Exp.	Ref
EVOO	10.24 ± 0.23	7.5 - 20	0.72 ± 0.03	0.3 - 3.5	3.17 ± 0.11	0.5 - 5.0	72.36 ± 0.45	55.0 - 83.0	6.87 ± 0.14	3.5 - 21.0	0.30 ± 0.02	< 1.5	0.55 ± 0.00	<0.8
GSO	7.05 ± 0.02	5.5 - 11.0	0.03 ± 0.00	nd - 1.2	3.65 ± 0.15	3.0 - 6.5	23.40 ± 0.10	12.0 - 28.0	64.08 ± 0.22	58.0 - 78.0	0.79 ± 0.05	nd - 1.0	0.24 ± 0.02	nd–1.0
SO	11.27 ± 0.10	8.0 - 13.5	0.09 ± 0.00	nd - 0.2	4.67 ± 0.12	2.0 - 5.4	22.76± 0.87	17 - 30	53.45± 0.17	48.0 - 59.0	6.88 ± 0.17	4.5 - 11.0	0.35 ± 0.03	0.1 - 0.6
WO	7.01 ± 0.09	6.1–7.4	0.08 ± 0.01	0.11–0.23	2.98 ± 0.11	1.5–2.75	17.23 ± 1.06	14.8–19.7	60.32± 1.54	59.5–64.7	12.98 ± 0.48	11.1–15.6	0.28 ± 0.01	-

Exp.= Results obtained from the experiment study; Ref = taken from references Codex Allimentarius. nd = not detected, with detection limit of 0.01%.

Figure 1. FTIR spectra of extra virgin olive oil (EVOO), grape seed oil (GSO), soybean oil (SO), and walnut oil (WO) scanned at the mid-infrared region (4000–650 cm⁻¹).

Figure 2. The Cooman plot for the classification of extra virgin olive oil (EVOO) and adulterated EVOO with other vegetable oils. (□) EVOO; (Δ) EVOO containing adulterants of grape seed oil (A); soybean oil (B); and walnut oil (C).

Table 2. Functional groups and vibration modes of peaks and shoulders of the FTIR spectra of extra virgin olive oil (EVOO) and other vegetable oils ^[13].

Assignment	Wavenumbers (cm^−1)	Functional group
(a)	3008	cis double-bond stretching
(b)	2954	Asymmetrical stretching vibration of CH3 (methyl group)
(c)	2925	Asymmetrical stretching vibration of CH2- (methylene group)
(d)	2852	Symmetrical stretching vibration of CH2- (methylene group)
(e)	1743	Ester carbonyl functional group of the triglycerides
(f)	1654	C=C stretching
(g)	1465	Bending vibrations of the CH2 and CH3 aliphatic groups
(h)	1417	Rocking vibrations of CH bonds of cis-disubstituted olefins
(i)	1377	Bending vibrations of CH2 groups
(j) and (k)	1236 and 1160	C-O stretching
(l) and (m)	1117 and 1098	Stretching vibration of the C-O ester group
(n)	1030	C-O stretching
(o)	962	Bending vibration of CH functional groups of isolated trans-olefin
(p)	850	=CH2 wagging
(q)	721	Overlapping of the methylene (-CH2) rocking vibration and to the out-of-plane vibration of cis-disubstituted olefins

Table 3. Multivariate calibration of partial least square (PLS) and principle component regression (PCR) for quantitative analysis of grape seed oil, soybean oil, and walnut oil as adulterants in extra virgin olive oil (EVOO)*.

Adulterant	Wavenumbers (cm^−1)	Multivariate Calib-ration	Spectra	Fac tor	Equation		R^2		RM SEC(% v/v)	RM SEP(% v/v)
					Calibration	Prediction	Calib- ration	Prediction
Grape seed oil	3018–3002 and 1200–1000	PLS	Normal	6	y = 0.999x - 0.003	y = 0.960x + 0.604	0.999	0.994	0.308	1.32
			1^st der	6	y = 0.999x + 0.008	y = 0.935x + 1.594	0.999	0.977	0.300	1.87
			2^nd der	9	y = 1.000x - 0.001	y = 0.891x – 0.843	0.999	0.829	0.039	6.43
		PCR	Normal	9	y = 0.998x + 0.023	y = 0.937x + 1.451	0.998	0.991	0.492	1.31
			1^st der	9	y = 0.997x + 0.054	y = 0.936x + 1.494	0.997	0.980	0.721	1.76
			2^nd der	9	y = 0.990x + 0.200	y = 0.906x – 0.916	0.990	0.858	1.39	5.53
Soybean oil	1200 – 1000, and 3018 - 3000	PLS	Normal	4	Y = 0.997x + 0.040	Y = 0.991x + 0.823	0.997	0.991	0.658	1.49
		PCR	1^st der	4	Y = 0.999x + 0.016	Y = 1.009x + 0.724	0.999	0.991	0.428	1.57
			2^nd der	5	Y = 0.999x + 0.003	Y = 0.949x + 1.281	0.999	0.958	0.226	2.28
			Normal	10	Y = 0.997x + 0.034	Y = 1.007x + 0.971	0.998	0.990	0.612	1.72
			1^st der	10	Y = 0.998x + 0.034	Y = 1.013x + 0.765	0.998	0.991	0.596	1.66
			2^nd der	10	Y = 0.995x + 0.070	Y = 0.955x + 1.159	0.995	0.949	0.886	3.10
Walnut oil	1125 – 667 and 3029–2954	PLS	Normal	8	y = 0.999x - 0.003	y = 1.044x - 0.427	0.999	0.998	0.101	0.934
			1^st der	8	y = 0.999x - 0.002	y = 0.961x + 1.148	0.999	0.987	0.006	1.86
			2^nd der	7	y = 1.000x - 0.004	y = 0.432x + 8.819	0.999	0.608	0.006	9.94
		PCR	Normal	9	y = 0.999x + 0.001	y = 1.042x - 0.428	1.000	0.998	0.100	0.908
			1^st der	10	y = 0.999x + 0.031	y = 0.954x + 1.123	0.999	0.991	0.567	1.51
			2^nd der	10	y = 1.000x + 001	y = 0.435x + 8.710	0.999	0.618	0.312	9.88

*Spectral treatments and multivariate calibrations chosen for the analysis of adulterants are italicized.

Lerma-García, M.J.; Ramis-Ramos, G.; Herrero-Martínez, J.M.; Simó-Alfonso, E.F. Authentication of Extra Virgin Olive Oils by Fourier-Transform Infrared Spectroscopy. Food Chemistry 2010, 118, 78–83.

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