Evaluation of Hexane Content in Edible Vegetable Oils Consumed in Iran

Milli-Q apparatus was utilized to supply deionized water (Billerica, MA, USA).The SPME apparatus with Carboxen (CAR)/PDMS–thickness 75 lm) coating fibers was supplied from Supelco(Bellefonte, PA, USA). The precondition of SPME fibers was done at 200°C for 10 min.

Analytical grade of hexane and chemical materials were supplied from Merck (Darmstadt, Germany).

In total, 40 oil samples (consisting of sunflower (n=6), corn (n=5), canola (n=2), frying (n=14) and blended oils (n=13)) of 24 brands were collected from Iranian market (Tehran, summer 2014). All the samples were stored at the dark room (25°C), in their original packages (Polyethylene terephthalate (PET)). The analysis all were performed in triplicate.

The solid phase microextraction Agilent Technologies 7890A GC system (SPME)-GC-(FID) (Palo Alto, CA, USA) which was coupled to a flame-ionization detector (FID)were used to determine residual hexane according to the Ligor and Buszewski (2008), Briefly, 50 mL of oil samples were placed in the HS vials (120 mL). Isolation step was carried out at 40 ± 1°C for 30 min without stirring. After that desorption was done for 5 min by the fiber in the injection port in where the temperature was adjusted 200°C (injector position –splitless). Then the oven temperature program was started (position–split). Separation was performed using The Stabilwax (Restek) column (30 m× 0.25 mm × 0.25 µm). The oven temperature program consisted of 3 min isothermal period at 40°C, then raised at 4°C/min increase to 100°C (held for 0 min), followed by increasing the temperature by 15°C/min to 190°C/min (held 4 min). Helium (99.999% purity) was utilized as a carrier gas with a pressure of 100 kPa. The temperature of split – splitless injector and the FID detector were adjusted 200°C ¹³.

Hexane is one of the most commonly used solvents not only in the edible oil industry but also in the process of herbal medicine and bioactive components production ^{14, 15}. So, hexane may be present in trace amounts in these kinds of products. A study has previously shown that 2,5-hexanedione which is derived from the metabolism of hexane is neurotoxic ¹⁶. Therefore, various maximum residual limit (MRL) has been determined for residual solvent in these products in order to reduce or eliminate chronic toxic effects of the solvents. So, in this study the hexane residue in 40 collected edible oil samples from of Iran market was evaluated. The limit of detection (LOD) and the limit of quantification (LOQ) were 3 µg/kg and 5µg/kg, respectively. The high correlation coefficients (0.981) indicated that there is a good linear behavior in the tested range (5-100 µg/kg). In this study, analysis of 40 oil samples described that 36 of them had hexane residue and its concentration ranged from < LOD to 42.6 µ/kg (Table 1). The results showed that 35% of the samples had hexane residue ranging from 5-42.6 µg/kg, while 10% of the samples were free of hexane and any hexane residue was detected in these 4 samples. The 55% of remaining samples had hexane residue, but it value was lower that LOQ.and LOD. As can be seen in Table 1 the highest hexane content as observed in canola oil. Based on the maximum residue limit of 1 mg/kg of hexane in the vegetable oils which is set by the European Union, none of the analyzed samples exceed the limit ⁸. There are only a few studies about the hexane residue in vegetable oils. Commercial orujo oil samples with various percentages of virgin olive oil (5–10%) were analyzed by Peña et al. (2003) for the presence of residual hexane and the results showed that almost all the samples were negative in term of hexane residue (lower than LOD) and just two samples had hexane at concentration of 2 and 3 mg/kg ³. The presence of solvent residue, including hexane, benzene, and toluene has been investigated by Michulec et al. (2004) in the different brands of primrose oil using HS- GC-FID. The value of 0.004, 0.009 and 0.017 mg/kg were achieved as limits of detection (LOD) for hexane, benzene, and toluene, respectively. They found that in all the primrose oils, the content of benzene was lower than LOD. Hexane residue in the most of the samples was lower than LOD, and only three samples had the value of 0.13, 0.16 and 0.70 mg/kg for hexane content ¹². Similarly, the content of toluene was lower than LOD in the most oil samples. Oh et al. (2005) found that hexane residue varied from trace amounts to 2.8 mg/kg in 87 commercial vegetable oils ⁹. Additionally, Ito et al. (2012) evaluated 23 annatto extract products for hexane residue by applying HS-GC/FID, and nearly 91% of the samples were free of hexane and only two samples containing hexane in the value of 0.6 and 0.7 mg/kg ¹¹. Ligor and Buszewski (2008) investigated the presence of some solvents including acetone, n-hexane, benzene, and toluene in various edible oils using SPME-GC-FID and SHS-GC-FID methods. A value of 0.003 and 0.002 mg/kg were obtained for a limit of detection by SPME-GC-FID and SHS-GC-FID methods, respectively. Their results showed that the residual amount of hexane in various vegetable oils was between 0.005 –0.460 mg/kg, which was below the permitted value of Polish norm (1000 mg/kg) ¹³. Jeong et al. (2017) developed HS-GC/MS method to evaluate hexane residue in health functional food products. They claimed that by applying this approach, it is likely to determine hexane residue in various kinds of these commodities. Their results showed that the average content of hexane in γ-Linolenic acid, omega-3 fatty acid, and conjugated linoleic acid was 0.39, 0.45 and 0.74 mg/kg, respectively. Furthermore, they achieved the value of 0.56 and 0.76 mg/kg as the mean content of hexane residue in lecithin and phosphatidylserine, respectively ¹⁴. Based on our study and similar research that evaluated the presence of hexane in the vegetable oils, bixin-based products, and some commercial functional food products, it seems that there is no concern about hexane residue in these commodities.