Research Article
Removal of di-2-ethylhexyl phthalate (DEHP) and mineral oil from crude hazelnut skin oil using molecular distillation – multiobjective optimization for DEHP and tocopherol
Beyza Gelmez1, Onur Ketenoglu2, Huseyin Yavuz3and Aziz Tekin2
1KOSGEB, Ankara, Turkey
2Department of Food Engineering, Ankara University, Ankara, Turkey
3Ana Gıda_Ihtiyac Mad. San. ve Tic. A.S S., BalS ıkesir, Turkey
Different distillation conditions of DEHP were investigated to decrease concentration in hazelnut skin oil. In a short-path distillation column, different absolute pressures (1–3 mbar) and evaporator temperatures (200–230°C) were used. When distilled at 230°C under 1 mbar of absolute pressure, a reduction of 98.95% of initial DEHP concentration was achieved. At this condition, DEHP concentration was found 0.32 mg/kg. Tocopherols were also removed by molecular distillation inevitably. At 220°C temperature and 3 mbar absolute pressure, total tocopherols were reduced from initial concentration of 780.63–419.24 mg/kg. Since tocopherols were desired to remain in hazelnut skin oil, a multiobjective optimization process was performed. When upper DEHP boundary was set to 1.5 mg/kg, 15 different alternative paths were reached while maximizing total tocopherol amount within pressure-temperature boundaries. After each molecular distillation, mineral oil content was reduced nearly by sixfold from an initial concentration of 64 mg/kg. Even when distillation temperature was set to 200°C, mineral oil content was drastically reduced to approximately 10 mg/kg level.
Practical applications:DEHP is a common contaminant in oil materials packed with plastic packages.
Removal of DEHP is of great importance due to negative health impacts. Since tocopherol loss should be kept minimum while processing oil for removal of DEHP, process conditions should be carefully selected. This study reveals optimum molecular distillation conditions for this purpose. These conditions could be evaluated in industrial plants for producing best quality products with maximum tocopherol content as possible.
Keywords:DEHP / Mineral oil / Molecular distillation / Multiobjective optimization / Tocopherol
Received: January 4, 2016 / Revised: February 19, 2016 / Accepted: March 31, 2016 DOI: 10.1002/ejlt.201600001
1 Introduction
DEHP [syn: Diethylhexyl phthalate, di-2-ethylhexyl phthal- ate, bis(2-ethylhexyl) phthalate] (PubChem CID: 8343) is a high molecular weight, odourless, oil-soluble, and water-insoluble phthalate with the chemical formula C8H4(C8H17COO)2. Guillaumeve and Ravetti [1] reported
a partial solubility of DEHP in water. As a plasticizer, DEHP is used in polyvinyl chloride (PVC) materials [2].
The most common contamination source of DEHP is the migration from plastic packages to food materials. Moreover, plastic parts of packages such as sewing ropes of bags may also be responsible for DEHP migration due to direct contact with food material. Institute for Agriculture and Trade Policy advises not to heat food material in plastic containers or not to use old or scratched packages in order to avoid from plastic contamination [3]. DEHP can migrate to food material during production, packaging, and storage. Breakfast cereals, bread, biscuits, cakes, and oils are mostly in contact with packages Correspondence:Prof. Aziz Tekin, Department of Food Engineering,
Ankara University, Ankara, Turkey E-mail:[email protected] Fax:0090-312-3178711
Abbreviations: DEHP, di-2-ethylhexyl phthalate; MOAH, mineral oil aromatic hydrocarbons;MOSH,mineral oil saturated hydrocarbons
Compliance with ethics requirements: This article does not contain any studies with human or animals.
containing plastics which are made by using DEHP [4]. It is reported that some factors like heat, pressure, presence of solvents, and radiation could increase migration of DEHP [5].
Ways of exposure to DEHP are not limited to food products but also inhalation and dermal exposure ways are possible [6].
Like other plastic materials, many negative effects of DEHP on human health have been reported. It is reported that DEHP has toxic effect on neural system, increases risk of cancer, and decreases fertility [7]. Also, researchers reported the linkage between obesity and DEHP recently [8].
Since there has been no strict regulation of DEHP limits in oil products, very low concentrations are in practice across global trade. For example, China’s upper limit for DEHP in food stuff is 1.5 mg/kg [9]. European Union’s tolerable daily intake (TDI) value of DEHP is reported as 37mg/kg of body weight/day [10].
There are some research about contamination of DEHP to oil and oil products. Serrano et al. [2] reported that they determined various concentrations of DEHP between 404 and 5591.7mg/kg in different oil products such as butter, margarine, and lard. In a recent research concerning the contamination of plasticizers to vegetable oils sold in US retail markets, researchers investigated 15 plasticizers in 21 oil products and detected DEHP in all products [11].
Mineral oil hydrocarbons (MOH) are hydrocarbons con- sisted of 10–50 carbon atoms. They could be divided into two main groups: Mineral oil aromatic hydrocarbons (MOAH) and mineral oil saturated hydrocarbons (MOSH) and latter could be present in most food products [12]. Besides, some materials like lubricating oil or solvents used in extraction of oil could be potential sources of MOSH. Fiselier and Grob [13]
reported that average MOSH concentration of analyzed commercial refined sunflower oils was found 11.2 mg/kg.
The aim of this study was to reduce DEHP concentration in crude hazelnut skin oil while protecting tocopherols by molecular distillation. For this purpose, multiobjective optimization was used to determine optimum molecular distillation conditions of DEHP and tocopherols. Also, removal of mineral oil content was aimed within this scope.
2 Material and methods
2.1 Material
Crude hazelnut skin oil which was produced by using pre- pressing solvent extraction method was kindly donated by S
C iftc iler Oil Company (Afyonkarahisar, Turkey).S 2.2 Methods
2.2.1 Molecular distillation equipment
Crude hazelnut skin oil was distilled using a KDL5 laboratory scale short-path distillation unit (UiC GmbH, Alzenau, Germany) with following parameters:
Ranges of absolute pressure (1–3 mbar) and evaporation temperature (200–230°C) were similar to the deodorization conditions of vegetable oil.
(1) Feed rate: 3 mL/min
(2) Evaporation surface area: 0.05 m2 (3) Wiper rotational speed: 240 rpm (4) Condensation temperature: 20°C
All distilled samples were stored at18°C until analyzed.
2.2.2 Determination of DEHP
DEHP was determined using a method according to Wu et al. [7]. A Shimadzu GC-2010 (Kyoto, Japan) gas chromatograph equipped with flame ionization detector (FID) and HP-5 capillary column (30 m0.32 mm id 0.25mmfilm thickness)(Agilent J&W, CA, USA) was used.
Injector and detector temperatures were 260 and 300°C, respectively. Columnflow had a rate of 8 mL/min in splitless mode. Oven temperature program was 60°C for 1 min, ramp to 220°C with 20°C/min rate, ramp to 290°C with 5°C/min rate, hold at 290°C for 2 min. Helium was used as carrier gas.
Detection limit was 0.1 mg/kg.
2.2.3 Determination of tocopherols
Tocopherol analyis was performed according to AOCS Ce 8–89 Official Method [14]. A Shimadzu SCL-10A HPLC system (Kyoto, Japan) equipped with a Hichrom Lichrosorb column (Reading, UK) with 5mm particle size was used. Column temperature was set to 25°C and hexane-isopropyl alcohol (99:1) was used as mobile phase with 1 mL/minflow rate.
2.2.4 Determination of mineral oil content
Mineral oil saturated hydrocarbons (MOSH) were first purified in a silver nitrate-impregnated silica column and then analyzed according to method described by Moret et al. [15]. A Shimadzu GC-2010 gas chromatograph equipped withflame ionization detector (FID) and HP-5 capillary column (30 m 0.32 mm id0.25mmfilm thickness)(Agilent J&W) was used.
Injector and detector temperatures were 320 and 350°C, respectively. Columnflow had a rate of 8 mL/min in splitless mode. Oven temperature program was 80°C for 2 min, ramp to 280°C with 12°C/min rate, ramp to 340°C with 7°C/min rate, hold at 340°C for 8 min. Helium was used as carrier gas.
Detection limit was 0.1 mg/kg.
2.2.5 Multiobjective optimization (MOO) of DEHP and tocopherols
Results for DEHP and tocopherol analysis were plotted on a 3D surface graph to show the effect of temperature and pressure on dependent variables. Quadratic model was
applied by using Statistica v10 (Statsoft, Tulsa, OK).
Multiobjective optimization (MOO) on these quadratic models was performed by an interactive MOO method called NIMBUS [16]. Maximizing tocopherols and mini- mizing DEHP concentration simultaneously were chosen as two objective functions which are dependent on pressure and temperature. Optimization of these functions used genetic algorithm within NIMBUS method. Objective functions, boundaries, and variables can be summarized as following:
0<MaxðTocopherolÞ ¼fTocopherolðP;tÞ<þinf inity ð1Þ
inf inity<MinðDEHPÞ ¼fDEHPðP;tÞ<1:5mg=kg ð2Þ where boundaries for P,t are: 1P3 in mbar; 200t 230 in degrees Celsius.
3 Results and discussion
Hazelnut skin oil was subjected to distillation using a molecular distillation unit at 1–3 mbar and 200–230°C in order to remove some contaminants as di-2-ethylhexyl phthalate (DEHP) and mineral oil of saturated hydrocarbons (MOSH). The effects of molecular distillation conditions on the tocopherols were also determined.
3.1 Removal of contaminants
Figure 1 shows the effects of absolute pressure and evaporation temperature during molecular distillation pro- cess on the DEHP concentration in hazelnut skin oil.
The results revealed that molecular distillation conditions
had positive effects on removal of DEHP from hazelnut skin oil. Initial concentration of DEHP in the oil was 30.41 mg/kg, while it was reduced to 0.32 mg/kg after distillation at 230°C evaporation temperature and 1 mbar absolute pres- sure. This removal corresponds to 98.95% of initial amount.
Increasing temperature at constant pressure caused decrease in DEHP concentration for all groups. Likewise, increasing vacuum or reducing absolute pressure at constant tempera- ture resulted in similar effect. It can also be seen from Fig. 2 that higher temperature and vacuum result in lower DEHP concentrations. Minimum values were placed on darker green regions, however distillation at such higher temper- atures like 230–235°C would undoubtedly have a negative effect on other quality properties of oil.
Adverse effects of DEHP on human health have been reported in many studies [7, 8] and some countries apply upper limit for DEHP in food stuff as 1.5 mg/kg. Figures 1 and 2 indicate that DEHP concentration could be reduced below 1.5 mg/kg by molecular distillation. The lowest temperature used in this study to reduce DEHP concentration below 1.5 mg/kg is 210°C when absolute pressure is 1 mbar. Higher pressures at 210°C did not result in lower DEHP concentration in the oil than targeted value. All distillationsperformed at 220 and 230°C could achieve to decrease DEHP concentration less than 1.5 mg/kg.
Crude vegetable oils may contain various amounts of mineral oils which can easily migrate to the oils by containers or solvents used in extraction. According to EFSA, the highest mean occurence values of MOSH in vegetable oils were between 41 and 45 mg/kg [12].
Figure 3 shows that molecular distillation achieved to drastically reduce initial mineral oil content of crude hazelnut skin oil. An initial MOSH concentration of 64 mg/kg could be reduced by nearly sixfold with distillation. After distillation, highest amount of MOSH was measured as 13.38 mg/kg at 210°C evaporator temperature and 2 mbar absolute pressure.
Figure 1. Comparison of DEHP concentrations in samples after molecular distillation.
The lowest MOSH content was measured as 5.58 mg/kg under 220°C–1mbar distillation conditions (Table 1). How- ever, it is almost impossible to get a regular trend in decreasing mineral oil by increasing temperature and reducing absolute pressure since it is a hard challenge to avoid contaminations of mineral oils during analysis.
Therefore, the deviations recorded between the results
may frequently occur. Chain-length distributions of MOSH fractions given in Table 1 showed that total MOSH amount mainly included three fractions with different ranges of carbon chain lengths such as: C(0)–C(15), C(16)–C(24), and longer than C(25). In crude oil, fractions having C(25) and longer carbon chains had the highest amount with 45.95 mg/kg. This fraction was significantly reduced lower Figure 2. Three-axis surface graph of DEHP versus P-T.
Figure 3. Total MOSH changes in crude hazelnut skin oil during distillation.
than 10 mg/kg during all distillation treatments, which corresponded to more than sevenfold of initial value. At 220°C–1mbar, C(16)–C(24) concentration was found the lowest among all treatments with a value of 1.45 mg/kg.
3.2 Protection of tocopherols
Tocopherols, known as antioxidants and have vitamin E activity, naturally exist in vegetable oils. It is desired to keep
them in the oils during refining but their concentrations always reduce in different proportions depending on the refining conditions. It was reported that crude hazelnut oil contains considerable amounts of tocopherols but 10% of them was removed from the oil during refining [17].
In this study, reductions in total tocopherol concen- trations were measured during molecular distillation of crude hazelnut skin oil which had a total tocopherol content of 780.63 mg/kg consisting of 461.76 mg/kg a-tocopherol, 15.25 mg/kgb-tocopherol, and 303.62 mg/kgg-tocopherol.
While removing DEHP and mineral oils from hazelnut skin oils by distillation, removal of tocopherols was also observed. As in Figs. 4 and 5, higher temperature and lower absolute pressure resulted in more losses in the oil. In other ways, higher absolute pressures and lower temper- atures tended to protect tocopherols better. However, DEHP and mineral oil concentrations are higher in these conditions. The results obtained in this study were then analyzed in order tofind the optimum conditions to protect tocopherols in the oils as much as possible by taking into account the conditions for reducing of DEHP under its targeted upper limits.
As previously mentioned that MOSH can be removed from the oil at all molecular distillation conditions. However, distillation temperature for removal of DEHP should be at least 210°C with 1 mbar of absolute pressure. The higher temper- atures with all applied pressures were suitable for removal of both DEHP and MOSH. When Fig. 4 is analyzed, it can be stated that the highest total tocopherol concentration above 210°C and 1 mbar was obtained about 400 mg/kg (exactly 419.23 mg/kg) at 220°C evaporation temperature and 3 mbar absolute pressure. These parameters can be considered as Table 1. Chain length distribution of MOSH in the samples
MOSH fractions, mg/kg C(0)–
C(15)
C(16)–
C(24) >C(25) Total
Crude hazelnut skin oil 4.1 13.95 45.95 64 Temp.
(oC)
Pressure (mbar)
200 1 0.86 3.09 7.24 11.19
2 1.53 3.83 3.49 8.85
3 0.66 3.11 3.16 6.93
210 1 0.72 4.15 7.41 12.28
2 1.35 5.36 6.67 13.38
3 1.16 3.93 3.18 8.27
220 1 0.34 1.45 3.79 5.58
2 0.97 5.83 5.81 12.61
3 0.41 3.65 2.24 6.30
230 1 0.20 4.28 4.95 9.43
2 0.72 4.80 5.60 11.12
3 1.10 2.96 3.61 7.67
Figure 4. Total tocopherol changes in crude hazelnut skin oil during distillations.
suitable conditions for distillation of crude hazelnut skin oil to remove the contaminants such as DEHP and MOSH.
Unlike DEHP, tocopherol measurements created a convex graph surface (Fig. 5). In red and darker red regions, tocopherols were observed to remain in material. As explained above, our suitable point representing 220°C evaporation temperature and 3 mbar absolute pressure was placed inside the limits of red region, where DEHP concentration was reduced below 1.5 mg/kg. According to Fig. 5, a low temperature-high pressure region seems to be more preferable without taking DEHP concentration into account. Although this figure itself could give satisfactory ideas about only one function (i.e., maximizing tocopherol content), evaluating this function while leaving the other objective function alone might lead to misleading results.
Results of optimization for functions inside boundaries are summarized in Table 2. For each case, an optimumP-t variable binary was generated for keeping DEHP mini- mum while maximizing tocopherol content. In order to reach the targets using NIMBUS system, 15 optimum alternatives were generated. In Pareto optimality, im- proved results for one of the objective functions could be obtained only by impairment of other function(s). Thus, priority was given to Function (2) to decrease DEHP below 1.5 mg/kg while compromising on maximizing Function (1). MOSH concentration was not defined as a function in multiobjective optimization, because its concentration could be reduced nearly sixfold in each distillation as stated above.
After 15 approaches, tocopherol content could be maximized up to 479.596 mg/kg while DEHP concentra- tion reached to its boundary level. Optimized pressure was found 2.340 mbar and optimized temperature was found 207.168°C at 15th generated alternative. All 15 paths that Figure 5. Three-axis surface graph of total tocopherols versus P-T.
Table 2. Generated alternatives for optimized variables and functions
Optimized variables
Alternatives
DEHP, f(min), mg/kg
Tocopherols, f(max), mg/kg
Pressure, mbar
Temperature,
oC
1 0.662 411.561 2.210 213.792
2 0.713 416.658 2.221 213.331
3 0.765 421.719 2.232 212.868
4 0.819 426.743 2.242 212.402
5 0.874 431.730 2.252 211.934
6 0.931 436.681 2.262 211.464
7 0.988 441.596 2.271 210.992
8 1.048 446.474 2.280 210.519
9 1.108 451.315 2.290 210.044
10 1.170 456.120 2.298 209.567
11 1.233 460.888 2.307 209.090
12 1.298 465.620 2.316 208.611
13 1.364 470.315 2.324 208.131
14 1.431 474.974 2.332 207.650
15 1.500 479.596 2.340 207.168
leaded us to our objective functions were then visualized to show the differences between them (Fig. 6).
According to Fig. 6, it can be stated that all these optimized paths seem feasible considering the limits of molecular distillation unit. In order to avoid the risk of high temperature, alternatives in the range of 9–15 could be suitable for studying at a maximum of 210°C or lower.
4 Conclusions
Initial DEHP concentration in crude hazelnut skin oil which was 30.41 mg/kg could be lowered below the limit values using molecular distillation. Application of both heat and vacuum helped for the reductions. Same effects could be observed when evaluating tocopherol amounts. An initial total tocopherol concentration of 780.63 mg/kg was reduced to 419.24 mg/kg after distillation at 220°C temperature and 3 mbar absolute pressure. However, excessive removal of tocopherols was not desired due to their antioxidative properties. Therefore, a multi objective optimization process was performed by using NIM- BUS method. Two objective functions were defined. One of them aimed to minimize DEHP concentration while other aimed to maximize tocopherol content. Aiming to keep our functions in our desired boundaries, 15 different paths were generated.
Mineral oil amount could also be reduced by molecular distillation. Even when distillation temperature was kept minimum at 200°C, total MOSH amount was reduced nearly sixfold. Therefore, this analysis was not processed within optimization procedure.
Authors thank to C iftS ciler Oil Company (Afyonkarahisar,S Turkey) for their kind donation of material for this study.
The authors have declared no conflict of interest.
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Figure 6. Value paths of alternatives aiming objective functions.