Quantitative determination of the iodine values of unsaturated plant oils using infrared and Raman spectroscopy methods

Figures & data

Table 1. Chemical characterization of the studied oils.

Fatty acids composition (%)	Oil
	Sunflower	Avocado	Hemp	High-linolenic flax	Safflower	Walnut	Roasted sesame	Rice	Corn	Rapeseed	Pumpkin seed	Low-linolenic flax	Hazel
C-14:0 Lauric acid	—	—	—	—	—	—	—	—	0.02	—	0.01	—	—
C-14:0 Myristic acid	0.08	—	—	—	0.11	—	0.03	0.34	0.04	0.05	0.11	—	—
C-16:0 Palmitic acid	3.58	17.33	5.99	5.91	6.93	7.27	10.11	20.05	10.15	4.39	12.3	6.23	6.13
C-16:1 Palmitooleic acid	0.11	6.62	—	—	0.07	—	0.21	0.17	0.11	0.19	—	—	—
C-18:0 Stearic acid	2.32	0.66	2.57	2.83	2.72	2.57	4.28	1.8	2.2	1.52	5.69	3.85	2.98
C-18:1 Oleic acid	86.24	59.62	11.88	11.27	11.33	17.08	41.58	42.7	31.98	58.38	35.34	16.27	77.62
C-18:2 Linoleic acid	5.23	9.06	56.49	15.68	77.22	60.12	41.51	31.83	53.91	18.4	44.51	70.98	10.65
C-18:3 Linolenic acid	0.41	0.68	20.97	63.13	0.19	11.22	0.58	1.04	0.75	8.83	0.26	1.65	—
C-20:0 Arachidic acid	0.15	0.04	—	—	0.34	—	0.33	0.59	0.27	0.37	—	—	—
C-20:1 Gadoleic acid	0.24	—	—	—	0.13	—	0.1	—	0.16	1.05	—	—	—
C-22:0 Behenic acid	0.5	—	—	—	0.11	—	—	—	—	0.09	—	—	—

Table 2. The fatty values determined in the present work.

Oil	IV (g/100 g fat)	AV (mg KOH/g fat)	PV (mw O2/1000 g fat)	SV (mg KOH/g fat)
Sunflower	84.6	3.27	1.46	188.17
Avocado	89.47	0.22	6.32	201.65
Hemp	173.43	1.45	4.64	194.25
High-linolenic flax	212.1	2.21	1.92	191.88
Safflower	161.34	1.11	6.53	202.66
Walnut	160.53	3.12	4.64	194.25
Roasted sesame	120.76	2.01	0.92	194.68
Rice	105.96	0.22	3.87	182.54
Corn	129.8	2.02	1.9	191.44
Rapeseed	113.04	0.63	3.72	189.09
Pumpkin seed	122.2	1.02	3.67	195.65
Low-linolenic flax	188.7	0.66	0.67	187.7
Hazel	84.6	0.34	0.59	183.03

IV: iodine value; AV: acidic value; PV: peroxide value; SV: soaping value.

Table 3. Wavenumbers observed in the IR and Raman spectra of the walnut oil.

Number	IR	Raman	Assignment^[Citation3,Citation22,Citation27,Citation30,Citation76]
1.	3005 m	3005 m	νas(= C-H) trans
2.	2952 msh	2954 msh	νas(CH3)
3.	2922 vs	2925 s	νas(CH2)
4.		2895 s	νas(CH2)
5.		2873 s	νs(CH3)
6.	2852 s	2853 vs	νs(CH2)
7.		2726 w	combination
8.	1742 s	1748 w	ν(C = O)
9.	1648 w	1655 m	ν(C = C)
10.	1463 m	1455 msh	δas(CH3) + δas(CH2)
11.		1438 m	δas(CH3) + δas(CH2)
12.	1418 vw		ρ(= C-H)
13.	1378 w		δs(CH3)
14.	1359 w	1362 vw	δs(CH2)
15.	1346 w		ω(CH2)
16.	1318 w		ω(CH2)
17.	1297 w	1303 m	τ(CH2)
18.	1279 w	1268 m	ω(CH2) + ν(C-O)
19.	1237 w		ν(C-O)
20.	1161 m		ν(C-O)
21.	1119 w	1117 vw	ν(C-C)
22.	1095 w		ν(C-C)
23.		1082 w	ν(C-C)
24.	1061 vw	1065 w	ν(C-C)
25.	1031 vw	1022 w	ν(C-C)
26.		971 vw	γ(= CH2)
27.	964 vw		δ(C-C = C)
28.	906 vw		γ(CH2)
29.		869 vw	γ(CH2)
30.	856 vw		γ(CH2)
31.		839 vw	γ(CH2)
32.	767 vw		γ(CH2)
33.	723 w	720 vw	γ(C-C-C)
34.	692 wsh		ρ(CH2) + γ(C-C-C)
35.	588 vw		ρ(CH2) + γ(C-C-C)

Table 4. The wavenumbers (ν) and integral intensity (A) of some selected bands from the IR and Raman spectra of the studied oils.

Oil	ν(CH2)				ν(C = C)
	IR		Raman		IR		Raman
	ν	A	ν	A	ν	A	ν	A
Hazel	2852	18.35	2853	28.67	1655	0.52	1655	1.79
Sunflower	2852	17.68	2852	20.81	1655	0.51	1655	1.32
Avocado	2852	16.95	2853	18.51	1655	0.50	1656	1.23
Rice	2852	20.77	2853	27.33	1656	0.81	1656	1.91
Rapeseed	2852	19.35	2853	20.66	1655	1.15	1655	1.58
Roasted sesame	2852	20.65	2854	23.99	1656	1.22	1655	1.62
Pumpkin seed	2852	16.13	2852	21.35	1656	0.93	1656	2.04
Corn	2853	15.80	2854	17.98	1655	0.98	1657	1.81
Walnut	2852	15.22	2854	21.00	1655	1.20	1655	2.41
Safflower	2852	17.64	2853	18.75	1655	1.56	1657	2.19
Hemp	2853	17.62	2852	18.14	1655	1.73	1657	2.35
Low-linolenic flax	2853	16.66	2852	12.46	1655	1.65	1657	2.00
High-linolenic flax	2852	18.48	2852	14.41	1655	2.37	1655	2.71

Figure 1. ATR/FT-IR spectra of oils A: Sunflower; B: Corn; C: Low-linolenic flax; D: High-linolenic flax; E: Walnut; F: Hazel; and G: Rapeseed.

Figure 2. ATR/FT-IR spectra of oils H: Roasted sesame; I: Avocado; J: Hemp; K: Safflower; L: Pumpkin seed; M: Rice.

Figure 3. Raman spectra of oils A: Sunflower; B: Corn; C: Low-linolenic flax; D: High-linolenic flax; E: Walnut; F: Hazel; G: Rapeseed.

Figure 4. Raman spectra of oils H: roasted sesame; I: avocado; J: hemp; K: safflower; L: pumpkin seed; and M: rice.

Figure 5. The relationship between the iodine value and integral intensity ratio of IR bands at about 1655/2852 cm⁻¹ of oils: A: hazel; B: sunflower; C: avocado; D: rice; E: rapeseed; F: roasted sesame; G: pumpkin seed; H: corn; I: walnut; J: safflower; K: hemp; L: low-linolenic flax; and M: high-linolenic flax.

Figure 6. The relationship between the iodine value and integral intensity ratio of Raman bands at about 1655/2850 cm⁻¹ of oils: A: hazel; B: sunflower; C: avocado; D: rice; E: rapeseed; F: roasted sesame; G: pumpkin seed; H: corn; I: walnut; J: safflower; K: hemp; L: low-linolenic flax; and M: high-linolenic flax.

Figure 7. The results of the PCA analysis. A: Loading from the first (PC-1) and second (PC-2) principal components of ATR-FTIR obtained for the studied oils; B: Explained variance from the PCs model.

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