The effects of UV radiation and X-ray on the oxidative stability of soybean oil were investigated. Also, rose oil was incorporated into soybean oil and its antioxidant activity was compared with that of α-tocopherol during accelerated storage. Treating the samples with radiation (UV and X-ray) stimulated the oxidation process in soybean oil in comparison with samples that did not receive radiation. X-rayed samples had significantly higher amounts of oxidation products than UV irradiated samples. The X-ray caused more oxidation in the samples due to its higher energy content. Also, the antioxidant activity of rose oil was comparable with that of α-tocopherol.
Irradiation involves the process of exposing raw and processed foods to ionizing and non-ionizing radiation. X-rays, gamma rays and electron beams are ionizing types of radiation, whereas UV, visible light, infrared, and microwave are non-ionizing types (Alothman
According to FAOSTAT, the worldwide production of SBO was 45.70 million tons in 2014. SBO is used in various foods including margarine, cooking and salad oils, mayonnaise and salad dressings. SBO is known for its low stability due to its high unsaturation content (Hammond
To the best of our knowledge, there are no reports on the effects of UV radiation and X-ray on the oxidative stability of SBO incorporated with rose oil. Given the varied impacts of ionizing and non-ionizing types of radiation on the process of oxidation in oils, the objective of the present study was to evaluate the oxidative stability of SBO by applying UV radiation and X-rays to the oil samples. Also, the antioxidant capacity of rose oil was compared with that of α-tocopherol.
All experimental chemicals were of analytical grade and were purchased from Merck Company (Darmstadt, Germany) and Sigma-Aldrich Company (St. Louis, MO). The SBO was refined, bleached and deodorized, while it did not contain any added antioxidants. The SBO was provided by Narges Shiraz Oil Company and the rose oil was provided by the Manely Company.
A gas chromatography (GC) (7890A, Agilent Technologies, Santa Clara, CA) was equipped with a HP-5MS capillary column (5% Phenyl Poly silphenylene-siloxane; 30 m length × 0.25 mm internal diameter; 0.25 μm film thickness) and was used accordingly. A mass spectrometer detector (5975C, Agilent Technologies, Santa Clara, CA) was operated at 70 eV electron ionization energy, in the electronic ionization mode, 0.5 s/scan, and a mass range of 50–480 atomic mass units. One μL of rose oil was injected into the GC/MS. Helium was used as the carrier gas at a flow rate of 1 mL/min. The injector was in split mode (at a ratio of 1:50) and its temperature was 280 °C. The oven temperature was programmed to increase from 60 °C to 210 °C at a rate of 3 °C/min. The temperature was finally increased to 240 °C at the rate of 20 °C/min and held at this temperature for 8.5 min. The total running time was 60 min. The interface line temperature was 280 °C. The MSD ChemStation Software (G1701EA, E.02.01.1177, Agilent Technologies, and Santa Clara, CA) was applied to analyze mass spectra and chromatograms. The compounds were identified by comparing their mass spectral fragmentation patterns with those in the data bank (Wiley/NBS). A quantitative analysis of EO compounds was made under the same chromatographic conditions using a GC coupled with a flame ionization detector (FID). The relative data in percentages were compiled from the electronic integration of the chromatogram peak areas.
DPPHº (2,2-diphenyl-1-picrylhydrazyl radical) scavenging activity of rose oil was evaluated according to the method described by Eblaghi
The IC50 value was calculated as a rose oil concentration that could provide 50% inhibition of the DPPHº activity. This is obtained from the graph plotting of the inhibition percentage against the concentration of rose oil.
The peroxide value (PV) and the anisidine value (AnV) were calculated according to the AOCS (American Oil Chemists’ Society) Official Methods Cd 8-53 and Cd 18-90, respectively (AOCS,
To determine the fatty acid composition, fatty acid methyl esters (FAMEs) of SBO were prepared according to the method described by Golmakani
SBO was divided into 3 groups of samples prepared separately: the control, rose oil (1000 mg/kg), and α-tocopherol (100 mg/kg). Each sample was divided into three equal portions, i.e. (a) non-irradiated samples, (b) X-rayed samples (exposed to 1 KGy and 140 kVp, radiography X-ray machine, radiography system, Gilardoni, Italy), and (c) UV irradiated samples (exposed to 31.40 KGy UVC, energy content of 8 eV, TUV30W G30T8, Philips lightening, Amsterdam, Netherland). Samples were then stored in an oven with a temperature that remained at 65 ± 1 °C under dark conditions for 21 days. The indicators of lipid oxidation were namely PV, AnV, and TV. These indicators were measured weekly. The K232 and K268 of SBO samples were determined at the end of storage.
The effectiveness of all the tested antioxidants was expressed as the Fvalue according to
where IPs is the induction period (IP) of the SBO containing antioxidants (rose oil and α-tocopherol) and IPc is the IP of the control, i.e. the SBO without any antioxidants. A PV higher than 20 indicates the poor flavor of SBO (O’Brien,
Antioxidant activity (AA) is a function of an antioxidant’s concentration and was calculated according to the following equation:
where [AH] is the antioxidant concentration in proper units (Antolovich
All tests were carried out in triplicate and mean values were calculated. SAS (Statistical Analysis Software, version 9.1; SAS Institute Inc. Cary, NC) was used for statistical analysis and significant differences were calculated using Duncan’s multiple range test (
Chemical composition of rose oil
No. | Chemical compound | Retention index | Relative peak area (%) |
---|---|---|---|
1 | Citronellol | 1226 | 36.68 ± 4.67 |
2 | n-Nonadecane | 1905 | 19.30 ± 1.36 |
3 | n-Heneicosane | 2103 | 9.39 ± 0.40 |
4 | 1-Nonadecene | 1872 | 7.19 ± 0.81 |
5 | Geraniol | 1255 | 4.52 ± 0.13 |
6 | n-Heptadecane | 1700 | 3.84 ± 0.49 |
7 | n-Eicosane | 2005 | 2.41 ± 0.03 |
8 | Phenyl ethyl alcohol | 1108 | 2.28 ± 0.13 |
9 | Methyl eugenol | 1405 | 2.26 ± 0.19 |
10 | n-Tricosane | 2301 | 1.73 ± 0.24 |
11 | Eugenol | 1358 | 1.54 ± 0.20 |
12 | n-Pentadecane | 1497 | 0.69 ± 0.05 |
13 | Germacrene D | 1478 | 0.60 ± 0.03 |
14 | n-Octadecane | 1797 | 0.49 ± 0.06 |
15 | trans-Rose oxide | 1125 | 0.46 ± 0.01 |
16 | Citronellyl acetate | 1353 | 0.45 ± 0.06 |
17 | n-Pentacosane | 2502 | 0.43 ± 0.03 |
18 | Linalool | 1098 | 0.42 ± 0.02 |
19 | 10-Heneicosene | 2091 | 0.37 ± 0.03 |
20 | 1-Eicosene | 1973 | 0.36 ± 0.05 |
21 | 1-Tricosene | 2289 | 0.31 ± 0.04 |
22 | Geranyl acetate | 1382 | 0.30 ± 0.02 |
23 | n-Docosane | 2199 | 0.27 ± 0.01 |
24 | α-Guaiene | 1436 | 0.26 ± 0.03 |
25 | Limonene | 1026 | 0.26 ± 0.01 |
26 | (E)-Caryophyllene | 1416 | 0.25 ± 0.03 |
27 | (Z,Z)-Farnesol | 1719 | 0.23 ± 0.00 |
28 | Phenyl ethyl octanoate | 1847 | 0.23 ± 0.01 |
29 | α-Humulene | 1451 | 0.22 ± 0.02 |
30 | α-Bulnesene | 1503 | 0.29 ± 0.04 |
31 | n-Hexadecane | 1597 | 0.21 ± 0.03 |
32 | Terpinen-4-ol | 1174 | 0.19 ± 0.01 |
33 | Heptanal | 901 | 0.19 ± 0.01 |
34 | Neryl acetate | 1364 | 0.18 ± 0.02 |
35 | n-Tetracosane | 2401 | 0.15 ± 0.00 |
36 | (E)-7-Octadecene | 1772 | 0.15 ± 0.02 |
37 | Methyl geranate | 1323 | 0.14 ± 0.00 |
38 | α-Pinene | 931 | 0.14 ± 0.01 |
39 | Benzyl benzoate | 1760 | 0.13 ± 0.01 |
40 | α-Terpineol | 1188 | 0.12 ± 0.02 |
41 | β-Elemene | 1390 | 0.10 ± 0.01 |
42 | Nerol oxide | 1151 | 0.10 ± 0.01 |
43 | n-Nonanal | 1102 | 0.10 ± 0.00 |
Mean ± standard deviation; Number of replicates: 2; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; Degree of significance:
The IC50 value of rose oil was 4.10 ± 0.70 mg/mL. Accordingly, rose oil can scavenge free radicals. The antioxidant properties of rose oil can be attributed to its chemical components such as citronellol, which present high antioxidant capacity (Wei and Shibamoto,
The PV was 1.99 meq O2/kg (
Initial characteristics of soybean oil
Characteristic | Amount |
---|---|
Peroxide value (meq O2/kg) | 1.99±0.22 |
Anisidine value (mg/kg) | 2.17±0.13 |
Totox value | 6.15±0.17 |
K232 | 0.10±0.00 |
K268 | 0.16±0.00 |
Fatty acid composition (%) | |
Palmitic acid; C16:0 | 11.05 |
Stearic acid, C18:0 | 4.99 |
Oleic acid; C18:1 (ω-9) | 24.53 |
Linoleic acid; C18:2 (ω-6) | 52.53 |
α-Linolenic acid; C18:3 (ω-3) | 6.43 |
Σ Saturated fatty acids | 16.04 |
Σ Monounsaturated fatty acids | 24.53 |
ΣPolyunsaturated fatty acids | 58.96 |
Mean ± standard deviation; Number of replicates for each analysis: 3; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; Degree of significance:
Changes in peroxide values of (a) non-irradiated, (b) UV irradiated, and (c) X-rayed soybean oil samples during accelerated storage (Mean ± standard deviation; Number of replicates for each analysis: 3; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; Degree of significance:
Except for X-rayed samples, the PVs of all other SBO samples were significantly increased during storage. Although the PVs of X-rayed samples showed an increasing trend until day 14 of storage, they decreased thereafter until the end of storage. The higher energy content of X-ray (Fan,
Rose oil and α-tocopherol had significantly lower PVs than the control. However, there were no significant differences between the PVs of rose oil and α-tocopherol.
Effects of UV radiation and X-ray on induction period (IP), Fvalue, and antioxidant activity (AA) of soybean oil
Sample | IP (day) | Fvalue | AA | K232 | K268 |
---|---|---|---|---|---|
Non-radiation | |||||
Control | 4.76 ± 0.11b |
1.00 ± 0.00b | 0.00 ± 0.00b | 13.91 ± 1.60b | 1.76 ± 0.29b |
Rose oil | 6.48 ± 0.20a | 1.36 ± 0.04a | 3.62 ± 0.42b | 14.61 ± 0.98b | 1.54 ± 0.20b |
α-Tocopherol | 5.96 ± 0.30a | 1.26 ± 0.06a | 25.11 ± 6.34a | 14.40 ± 1.79b | 1.45 ± 0.25b |
UV radiation | |||||
Control | 2.71 ± 0.47d | 1.00 ± 0.00d | 0.00 ± 0.00b | 13.08 ± 0.01b | 1.07 ± 0.68b |
Rose oil | 3.73 ± 0.63c | 1.38 ± 0.23c | 3.75 ± 2.33b | 17.74 ± 0.08b | 2.21 ± 0.13b |
α-Tocopherol | 3.47 ± 0.25c | 1.28 ± 0.10c | 28.05 ± 9.40a | 17.96 ± 0.10b | 2.25 ± 0.15b |
X-ray | |||||
Control | 0.97 ± 0.38e | 1.00 ± 0.00f | 0.00 ± 0.00d | 20.91 ± 2.69a | 6.27 ± 0.38a |
Rose oil | 1.10 ± 0.07e | 1.14 ± 0.08e | 1.34 ± 0.74d | 19.48 ± 0.40a | 5.62 ± 0.00a |
α-Tocopherol | 1.06 ± 0.06e | 1.09 ± 0.06e | 8.76 ± 6.56c | 18.76 ± 0.68a | 6.15 ± 0.08a |
Mean ± standard deviation; Number of replicates for each analysis: 3; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; In each column, means with different letters are significantly different (
The Fvalues of irradiated samples were lower than those of non-irradiated samples. The Fvalue of rose oil was significantly higher than that of the control. Therefore, rose oil can be regarded as an effective antioxidant in this context because of its ability to improve the oxidative stability of SBO. In this respect, significant differences were not observed between the Fvalues of rose oil and α-tocopherol.
X-rayed samples had lower AAs compared to non-irradiated samples. Although there were no significant differences between the AAs of rose oil and the control, α-tocopherol caused a significantly higher AA. Since AA depends on the concentration of antioxidants, the AA of α-tocopherol was used at a lower concentration and therefore became significantly higher than rose oil.
The AnVs of the SBO samples during accelerated storage are illustrated in
Changes in anisidine values of (a) non-irradiated, (b) UV irradiated, and (c) X-rayed soybean oil samples during accelerated storage (Mean ± standard deviation; Number of replicates for each analysis: 3; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; Degree of significance:
The AnVs of the samples increased significantly with a longer storage time. Although there were no significant differences between the AnVs of rose oil and α-tocopherol, the AnVs of both rose oil and α-tocopherol were significantly lower than that of the control. Keramat
Changes in Totox values of (a) non-irradiated, (b) UV irradiated, and (c) X-rayed soybean oil samples during accelerated storage (Mean ± standard deviation; Number of replicates for each analysis: 3; Statistical test: ANOVA and multiple comparison of means using Duncan’s test; Degree of significance:
The K268 values of the X-rayed samples were significantly higher than those found in non-irradiated and UV irradiated samples. The K268 values of the control, rose oil, and α-tocopherol were not significantly different.
Effects of UV radiation and X-ray were evaluated on the oxidative stability of SBO incorporated with rose oil. Radiation induced higher levels of oxidation processes in the SBO samples. Furthermore, the exposure of samples to X-ray caused significantly higher amounts of oxidation products compared to samples exposed to UV irradiation. The higher intensity of oxidation that occurred in the X-rayed samples can be attributed to the higher energy content of X-rays. Generally, the antioxidant capacity of rose oil was comparable with that of α-tocopherol. Therefore, rose oil can enhance the oxidative stability of irradiated SBO.
The authors gratefully acknowledge the financial support of the Research Affairs Office at Shiraz University. We would like to thank Narges Shiraz Oil Company for providing the SBO. The authors would like to thank Dr. Mehdi Zehtabian. In addition, we thank the language editor Mohsen Hamedpour-Darabi for editing the paper.