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Time-temperature study of the kinetics of migration of diphenylbutadiene from polyethylene films into aqueous foodstuffs
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Food Research International 41 (2008) 138–144 www.elsevier.com/locate/foodres
Time-temperature study of the kinetics of migration of diphenylbutadiene from polyethylene films into aqueous foodstuffs A. Sanches Silva a, J.M. Cruz Freire a, R. Franz b, P. Paseiro Losada a,* a
Department of Analytical Chemistry, Nutrition and Food Science, Faculty of Pharmacy, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain b Fraunhofer Institut fu¨r Verfahrenstechnik and Verpackung, Freising, Germany Received 25 June 2007; accepted 23 October 2007
Abstract The objective of this work is to study the migration of the model migrant 1,4-diphenyl-1,3-butadiene (DPBD) from a low density polyethylene (LDPE) film into two representative aqueous foodstuffs in comparison to EU official food simulants. Orange juice and tomato ketchup samples were put into contact with the additivated plastic inside a migration cell. Then, samples were stored at different time-temperature conditions. The extraction was carried out with hexane and acetonitrile. Extracts were analyzed by HPLC–UV and DPBD was detected at 330 nm. Results showed that migration was not detectable in tomato ketchup and aqueous food simulants A and B (water and 3% acetic acid), whereas DPBD has migrated into orange juice. Acetic acid and water may be appropriate simulants for tomato ketchup but not for orange juice. The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1at 5, 25 and 40 °C, respectively, indicating that the diffusion in orange juice is about 4 orders of magnitude slower in the LDPE films. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Migration; DPBD; Mathematical modelling; Diffusion coefficients; Tomato ketchup; Orange juice; Cloudy beverages
1. Introduction Food packaging has the important role of protecting foodstuffs during storage and distribution. Moreover, it can avoid or at least delay the products spoilage and degradation and therefore, increasing their shelf-life. However, plastics intended for food contact, which are the most used packages by the food industry are not inert (Risch, 2000) and they can interact with the surrounding environment. They are three main food-packaging interactions: sorption, permeation and migration. The sorption of components by the food packaging, has been the most studied interaction *
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0963-9969/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2007.10.007
phenomenon regarding orange juice. It was established that several components like free fatty acids and aroma volatiles could be absorbed by the polymer from the orange juice (Pieper & Petersen, 1995; Pieper, Borgudd, Ackermann, & Fellers, 1992; Willige, Van Linssen, Legger-Huysman, & Voragen, 2003). Permeation of substances through packaging materials can result in both a change in the food flavour and a loss of flavour intensity (Risch, 2000). Migration, which is the transference of components from the packaging into the food product, is the interaction phenomenon that claims more attention in what respects to food safety because chemicals that migrate into food may be potentially dangerous for health. Due to the importance of this matter, the European Union (EU) has established specific
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legislation. According to the Frame Regulation (EC) No. 1935/2004, all materials and articles intended to come in contact with foods should not transfer their constituents into food in quantities which could endanger human health or bring about unacceptable changes in composition or characteristics of foodstuffs. Directive 2002/72 includes a list of authorized substances that may be used in the manufacture of materials intended for food contact. According to the EU directive 85/572/EEC it is prescribed to perform migration tests in defined food simulants. The simulants for non-alcoholic beverages like fruit or vegetable juices are water, distilled or equivalent quality (simulant A). If the food pH value is equal to or less than 4.5, then 3% acetic acid (w/v) (simulant B) is used. The directive 2002/72/EC accepts migration estimation as long as valid models based on scientific evidence can be applied. The prediction of migration can be an excellent tool to support legislating agencies to make regulatory decision and to help food and packaging industries during packaging formulations. This approach saves time, economic and human resources. Many papers have already referred the importance of valid mathematical models to predict chemical migration from packaging into foodstuffs (Begley et al., 2005; Begley, 1997; Brandsch, Mercea, Tosa, & Piringer, 2002; Duffy, Hearty, Mccarthy, & Gibney, 2007; Hamdani, Feigenbaum, & Vergnaud, 1997; Petersen, Trier, & Fabech, 2005; Stoffers et al., 2005) and to estimate exposure to food-packaging migrants (Duffy & Gibney, 2007; Vitrac & Leblanc, 2007; Vitrac, Challe, Leblanc, & Feigenbaum, 2007). Nevertheless there are still scarce data concerning the estimation of migration key parameters (diffusion coefficients and partition coefficients) in real foodstuffs, especially aqueous foodstuffs. We have carried some previous works regarding the prediction of migration in different meat products (Sanches Silva, Cruz Freire, Sendo´n Garcı´a, Franz, & Paseiro Losada, 2007a) and in spread chocolate, chocolate and margarines (Sanches Silva, Cruz Freire, Sendo´n Garcı´a, Franz, & Paseiro Losada, 2007b, in press-c). Regarding the migration studies in orange juice, Rodushkin and Magnusson (2005) have studied the transfer of aluminium from laminated paperboard packages and more recently ITX, a photoinitiator, has also been studied by Sagratini, Man˜es, Giardina´, and Pico (2006) and Sun, Chan, Lu, Lee, and Bloodworth (2007). The aim of this work was to study the migration of the model migrant 1,4-dyphenyl-1,3-butadiene (DPBD) from a packaging film into two aqueous foodstuffs, tomato ketchup and orange juice. Moreover, acetic acid and water were checked for their suitability as aqueous foodstuffs simulants. Parameters that influence migration phenomena were evaluated and the mechanism of the migration of chemicals into these two food items was discussed. Effective diffusion coefficients were calculated according to a proposed mathematical model that allows the migration prediction of DPBD in orange juice.
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2. Experimental 2.1. Chemicals, standards and samples Acetonitrile (ACN), ethanol, acetic acid and hexane were purchased from Merck (Darmstadt, Germany). Ultrapure water was prepared using a Milli-Q filter system (Millipore, Bedford, MA, USA). Diphenylbutadiene (DPBD) had a purity of 98% and it was supplied by Sigma–Aldrich (Steinheim, Germany). A primary stock solution of DPBD was prepared in ethanol (1.0 mg/ml). Intermediate standard solutions of DPBD were prepared, by dilution, (0.1–10.0 lg/ml) for the calibration curve. The calibration curve consisted of a plot of peak area against the concentration of the standard calibration solutions. Solutions were stored in a refrigerator (5 °C). Orange juice and tomato ketchup were kindly supplied by the Foodmigrosure Consortium (EU Foodmigrosure Project, 2003). 2.2. Polymeric films The film used was a candidate certified reference material (CRM) for specific migration testing. It is an LDPE film (thickness 444 lm; density 0.912 g/cm3) spiked with 1,4-diphenyl-1,3-butadiene (DPBD) (CAS No. 538-81-8, MW = 206.3) and was produced by Fraunhofer IVV (Freising, Germany) according to a defined and recognised protocol (Specific Migration EU project, 2000; O’Brien et al., 1997; Stoffers et al., 2004). The initial concentration of the migrant in the polymer (CP,0) was 121.4 mg kg1. This corresponds to an area related maximum migration value of 491.6 lg/dm2. 2.3. Migration tests Samples (tomato ketchup and orange juice) and simulants (water and acetic acid 3%) (10 mL) were put into contact with the plastic containing the DPBD inside a migration cell (one-side contact and 0.1 dm2 of surface). Orange juice was analysed at 3 different temperatures and tomato ketchup at 2 temperatures. Table 1 shows the storage conditions used. A total of 10 samples were prepared for each kinetic curve for each aqueous foodstuff and temperature. Kinetic curves were carried out by duplicate. Samples were prepared previous HPLC analysis as described below. Table 1 Migration tests conditions for orange juice and tomato ketchup Food item
Storage temperature (°C)
Test conditions
Orange juice
5 25 40 25 70
2, 1, 1, 1, 2,
Tomato ketchup
4, 2, 2, 2, 4,
10, 20, 30 d 4, 10, 20 d 4, 6, 10 d 4, 10, 20 d 8, 16, 24 h
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Simulants migration tests were carried out at 40 °C for 10 days, also by duplicate and injected directly in the HPLC–DAD.
Table 3 Results of the tests carried out to understand the mechanism of migration of DPBD from LDPE films into orange juice Test
Description
DPBD concentration (mg/L)
1 2
Whole orange juice Orange juice after centrifugation, it means orange juice without coarse insoluble solids Orange juice centrifuged and filtered by 0.5 lm filter,it means orange juice without practically all insoluble solids Orange juice after hexane extraction, it means without organic substances extractable by hexane Water with benzene (approx. 0.08%) Water with hexane (approx. 0.04%) Solid residue after centrifugation dispersed in water
1.53 0.61
2.4. Samples extraction Orange juice and tomato ketchup samples (10 mL) were extracted with 2 20 mL of hexane and centrifuged at 3000 rpm (1036g) for 5 min. Then, the organic phase was separated by centrifugation and supernatants were pooled and evaporated in a rotary evaporator. The residue was dissolved with 10 mL of ACN. Previous HPLC–DAD analysis, solutions were filtered (Sendo´n, Sanches Silva, & Paseiro, 2004). 2.5. HPLC–UV conditions The HPLC system (Hewlett-Packard, Waldbronn, Germany) was fitted with a HP1100 quaternary pump, a degassing device, an autosampler, a column thermostatting system and a diode array UV detector. The detector was continuously performing a scan in the range 190–400 nm. The wavelengths used for diphenylbutadiene quantification was 330 nm, which corresponds to its highest absorbance peaks in UV scanning. The analysis was performed using acetonitrile (ACN) and water as mobile phase. The solvents gradient is shown in Table 2. The HP ChemStation chromatographic software was used for data acquisition. Chromatographic separation was performed with a Kromasil 100 C18 (15 cm 0.4 cm I.D., 5 lm particle size) (Teknokroma, Barcelona, Spain) at 30 °C. The flow-rate was 1.0 mL/ min and the injection volume was 50 lL. Diphenylbutadiene was identified by comparison of its retention time and UV spectra with those of an injected pure standard using the same HPLC conditions. 2.6. Tests to understand the migration mechanism of DPBD in orange juice These tests were carried out in hermetically closed centrifuge tubes. A small piece of film spiked with DPBD (1 2.5 cm) was immersed in the different matrices for 36 h at 70 °C. After this period, the plastic films were removed and 1 mL of the extract was diluted with 1 mL of acetonitrile. The solutions were then filtered prior to HPLC analysis. The tests conducted were summarized in Table 3.
Table 2 Solvents gradient of HPLC method Time (min)
Acetonitrile (%)
Water (%)
0 2 17 30
65 65 100 100
35 35 0 0
3
4 5 6 7
0.10
0.68 0.02 0.01 0.29
2.7. Mathematical models Eq. (1) (Crank, 1975; Han, Selke, Downes, & Harte, 2003) is commonly used to calculate key parameters of migration (diffusion and partition coefficients). " # 1 X M F;t 2að1 þ aÞ Dq2n t ¼1 exp ð1Þ 1 þ a þ a2 q2n M F;1 L2p n¼1 where MF,t is migrant amount in food at time t (lg); MF,1 is migrant amount in food at equilibrium (lg); a is the mass ratio of migrant in food to that in packaging film at equilibrium; D is the diffusion coefficient (cm2/s); Lp is the thickness of packaging film (cm); qn is the positive roots of the equation tan qn = a qn; t is the migration time (s). In the present work, diffusion coefficients were calculated using the simplest Eq. (2) (Crank, 1975) because Eq. (1) would require a very large number of roots. " # s 1=2 s M F;t 2 ¼ ð1 þ aÞ 1 e a erfc 2 a M F;1 ð2Þ Dt with s ¼ 2 Lp This equation also is recommended by FDA to model the sorption, at a fixed temperature, of any substances in plastic (FDA Guidance for Industry, 2006). In our case, D is an effective diffusion coefficient for the whole polymer-orange juice system. In this way a simplified but pragmatic mathematical model can be applied. Experimental data for orange juice and tomato ketchup were fitted to Eq. (2), by nonlinear regression, with commercial software (Solver of Microsoft Excel 2003). The root of the mean-square error % (RMSE(%)) was calculated using Eq. (3). This measure the fit between experimental and estimated data (Helmroth, Dekker, & Hankemeier, 2002):
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RMSEð%Þ ¼
1 M P;0 rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 XN 2 ððM F;t Þexperimental;i ðM F;t Þpredicted;i Þ i¼1 N 100 ð3Þ
where N is the number of experimental points per migration curve; i is the number of observations; MP,0 is the initial amount of the migrant in the polymer (lg). 3. Results and discussion
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Migration test were also carried out in 3% acetic acid and water at 40 °C for 10 days and results revealed there was no migration of DPBD from the same film. Tomato ketchup results are in agreement with those found for aqueous simulants. These findings can be explained by the high lipophilicity of DPBD which leads to negligible migration which is below the analytical detection limit. On the other hand, DPBD has migrated into orange juice with the highest DPBD concentration at 30 lg/dm2 obtained at 25 °C after 20 days of food/plastic contact. This means acetic acid and water may be appropriate simulants for tomato ketchup but not for orange juice.
3.1. DPBD migration in simulants, orange juice and tomato ketchup
3.2. Tests to understand DPBD migration in orange juice
The extraction procedure has been validated previously for orange juice and the recovery at 1 mg/kg was 85.2% (Sendo´n et al., 2004). Fig. 1 shows a typical chromatogram of an orange juice sample with DPBD as a result of foodstuff-plastic contact. In the present paper, tomato ketchup has been extracted with the same method as orange juice. Recovery has been checked using the standard addition procedure. At 1 mg/kg, the recovery was 86.78%. Migration of DPBD in tomato ketchup was not detected at 25 °C (DL = 3 lg/dm2). Accelerated migration tests were carried out at more severe conditions of temperature (70 °C) in tomato ketchup and migration was also not found.
In order to understand the migration mechanism of DPBD in orange juice (a representative beverage which is typically cloudy and not a clear liquid) we have carried out different rapid accelerated migration experiments at 70 °C for 36 h (Table 3). From tests 1, 2 and 3, we concluded that migration decreases as the quantity of insoluble solids is lowered in orange juice, without coarse insoluble solids migration decreases 60% and when orange juice is filtered through 0.45 lm then the decrease is 93%. This means that the presence of solids in the juice is the main and almost only factor responsible for detectable DPBD migration into orange juice. Because orange juice has a very small ‘‘fat” content (0.2% or less) (USDA database, 2006) and in order to study
Fig. 1. HPLC chromatogram of an orange juice sample after contact with PE-plastic film additivated with DPBD.
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the influence of this parameter in the migration process, three other tests were carried out (test 4, 5 and 6). Test 4 shows that substances extractable by hexane (its equivalent to fat content) play, in principle, an important role in the migration phenomenon, in orange juice without ‘‘fat” migration decreases 56%. However, it is important to stress that when orange juice is extracted with hexane the structure of orange juice is clearly modified, therefore the influence of substances extracted with hexane from orange juice should be target of study in the future. On the other hand, it is known that dissolved organic matter (DOM) in water increases the solubility of hydrophobic organic chemicals (Akkanen, Lyytika¨inen, Tuikka, & Kukkonen, 2005; Hunchak-Kariouk, Schweitzer, & Suffet, 1997). In order to test both the influence of DOM in the migration of DPBD to aqueous solutions and the effect of remaining hexane in orange juice after extraction, both an aliphatic (hexane) and an aromatic (benzene) molecules were added to water and migration test were carried out (tests 5 and 6). Results showed that migration was increased (0.01–0.02 mg/L) against water migration (n.d.), but it is insignificant comparing with the migration into orange juice. Therefore, DOM only is not a key parameter for the explanation of the migration of DPBD in orange juice. It seems that ‘‘fat” content linked with insoluble solids are the main factor to explain the DPBD migration into orange juice. Test 7 has given an interesting results because this kind of ‘‘new aqueous simulant” constitute by coarse insoluble solids separated by centrifugation from orange juice and dispersed in water showed a high migration (0.29 mg/L) against water (n.d.). It seems clear that insoluble solids are the main parameter that influence in the migration of DPBD in orange juice, probably it is powered by the presence of ‘‘fat” substances in the orange juice. Our results are in agreement with the recent work published by Sagratini et al. (2006) on the migration of isopropyl thioxanthone (ITX, photoinitiator) from packaging to foodstuffs. They attributed the migration of lipophilic ITX in milk to the presence of fat. Whereas the migration of ITX in orange juice was caused by the juice fibers which interact with the compound. 3.3. Mathematical models and determination of key parameters The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1 at 5, 25 and 40 °C, respectively. Taking into account that the diffusion coefficients in the polyethylene film for DPBD would be much lower and typically at 40 °C in the range of 1 108 cm2 s1 (Stoffers, 2004) the migration speed limiting step occurs in the orange juice at diffusion rate which is 3–4 order lower than in the polyethylene film. Again this can only be explained when
Fig. 2. Experimental and predicted migration values of DPBD into orange juice at 5, 25 and 40 °C.
solids in the otherwise liquid matrix dominate the migration process. More specifically, the explanation for this remarkable effect of a slowing down of the migration process of DPBD in orange juice can be found in the combination of two mass transport processes: (1) the transport from the plastic film to the aqueous phase and then (2) the adsorption and further absorption of the DPBD from the aqueous medium by insoluble solids which may be the slowest process. Another reason may be due to the direct mass transport of DPBD from the packaging to the insoluble solids may occur but this appears rather unlikely. Low RMSE(%) were found at the three temperatures (0.2, 0.7 and 0.5% at 5, 25 and 40 °C, respectively), showing that there is a good correlation between experimental and estimated migration values (Fig. 2). This indicates that this model can be used to predict DPBD migration into orange juice. 4. Concluding remarks In the present study, the migration of DPBD from PE films was studied in two aqueous foodstuffs, tomato ketchup and orange juice. Results showed that migration was negligible for tomato ketchup but not for orange juice. According to our results, the official EU food simulants A and B for migration tests are not suitable for orange juice and other high fiber products. Leaching of chemicals into cloudy juices and clear beverages should be considered differently. Migration of DPBD into orange juice is due to the presence of insoluble solids that concentrate DPBD from the aqueous phase of orange juice in which DPBD is very low soluble. Effective diffusion coefficients of DPBD into orange juice were calculated using a mathematical modelling based on Fick’s second Law. The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1 at 5, 25 and 40 °C, respectively, about
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3–4 orders of magnitude less than the in LDPE film (Stoffers, 2004). Acknowledgments The study was financially supported by EU Contract No. QLK1-CT2002-2390, Foodmigrosure and the Xunta de Galicia (Project No. PGIDIT05TAL20301PR). The Foodmigrosure Project is financially supported by the European Commission, under the Thematic Programme Quality of life and Management of Living Resources, Key Action 1 on Food, Nutrition and Health. The conclusions are the sole responsibility of the authors and do not represent the opinion of the European Commission. Authors are grateful to the ‘‘Ramo´n y Cajal” Program financed by the Ministry of Education of Spain and to the ‘‘Fundacßa˜o para a Cieˆncia e Tecnologia”, Portugal, for the Postdoctoral fellowship of Ana Sanches Silva. The authors are grateful to Ms. Patricia Blanco Carro and Mr. Gonzalo Hermelo Vidal for their excellent technical assistance. References Akkanen, J., Lyytika¨inen, M., Tuikka, A., & Kukkonen, J. (2005). Dissolved organic matter in pore water of freshwater sediments: Effects of separation procedure on quantity, quality and functionality. Chemosphere, 60(11), 1608–1615. Begley, T., Castle, L., Feigenbaum, A., Franz, R., Hinrichs, K., Lickly, T., et al. (2005). Evaluation of migration models that might be used in support of regulations for food-contact plastics. Food Additives and Contaminants, 22(1), 73–90. Begley, T. H. (1997). Methods and approaches used by FDA to evaluate the safety of packaging. Food Additives and Contaminants, 14(6–7), 545–553. Brandsch, J., Mercea, P., Tosa, V., & Piringer, O. (2002). Migration modeling as a tool for quality assurance of food packaging. Food Additives and Contaminants, 19(Suppl.), 29–41. Crank, J. (1975). The mathematics of diffusion (2nd ed.). Oxford: Clarendon, pp. 44–68. Duffy, E., & Gibney, M. J. (2007). Use of food-consumption database with packaging information to estimate exposure to food-packaging migrants: Expoxidized soybean oil and styrene monomer. Food Additives and Contaminants, 24(2), 216–225. Duffy, E., Hearty, A. P., Mccarthy, S., & Gibney, M. J. (2007). Estimation of exposure to food packaging materials. 3.: Development of consumption factors and food-type distribution factors from data collected on Irish children. Food Additives and Contaminants, 24(1), 63–74. EU directive 85/572/EEC laying down the list of simulants to be used for testing migration of constituents of plastic materials and articles intended to come into contact with foodstuffs. EU Official Journal L372 of 31.12.1985; 14–21. EU directive 2002/72/EC relating to plastics materials and articles intended to come into contact with foodstuffs. EU Official Journal L220 of 15.08.2002; 18–55. EU Project ‘‘Specific Migration” Certified reference materials for specific migration testing of plastics for food packaging needed by industry and enforcement laboratories. Project supported by European Commission under Contract No. (G6RD-CT-2000-00411). EU Project ‘‘Foodmigrosure” (Modelling migration from plastics into foodstuffs as a novel and cost efficient tool for estimation of consumer (plastic-food) for estimation of exposure from food contact materials).
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Time-temperature study of the kinetics of migration of diphenylbutadiene from polyethylene films into aqueous foodstuffs A. Sanches Silva a, J.M. Cruz Freire a, R. Franz b, P. Paseiro Losada a,* a
Department of Analytical Chemistry, Nutrition and Food Science, Faculty of Pharmacy, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain b Fraunhofer Institut fu¨r Verfahrenstechnik and Verpackung, Freising, Germany Received 25 June 2007; accepted 23 October 2007
Abstract The objective of this work is to study the migration of the model migrant 1,4-diphenyl-1,3-butadiene (DPBD) from a low density polyethylene (LDPE) film into two representative aqueous foodstuffs in comparison to EU official food simulants. Orange juice and tomato ketchup samples were put into contact with the additivated plastic inside a migration cell. Then, samples were stored at different time-temperature conditions. The extraction was carried out with hexane and acetonitrile. Extracts were analyzed by HPLC–UV and DPBD was detected at 330 nm. Results showed that migration was not detectable in tomato ketchup and aqueous food simulants A and B (water and 3% acetic acid), whereas DPBD has migrated into orange juice. Acetic acid and water may be appropriate simulants for tomato ketchup but not for orange juice. The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1at 5, 25 and 40 °C, respectively, indicating that the diffusion in orange juice is about 4 orders of magnitude slower in the LDPE films. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Migration; DPBD; Mathematical modelling; Diffusion coefficients; Tomato ketchup; Orange juice; Cloudy beverages
1. Introduction Food packaging has the important role of protecting foodstuffs during storage and distribution. Moreover, it can avoid or at least delay the products spoilage and degradation and therefore, increasing their shelf-life. However, plastics intended for food contact, which are the most used packages by the food industry are not inert (Risch, 2000) and they can interact with the surrounding environment. They are three main food-packaging interactions: sorption, permeation and migration. The sorption of components by the food packaging, has been the most studied interaction *
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0963-9969/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2007.10.007
phenomenon regarding orange juice. It was established that several components like free fatty acids and aroma volatiles could be absorbed by the polymer from the orange juice (Pieper & Petersen, 1995; Pieper, Borgudd, Ackermann, & Fellers, 1992; Willige, Van Linssen, Legger-Huysman, & Voragen, 2003). Permeation of substances through packaging materials can result in both a change in the food flavour and a loss of flavour intensity (Risch, 2000). Migration, which is the transference of components from the packaging into the food product, is the interaction phenomenon that claims more attention in what respects to food safety because chemicals that migrate into food may be potentially dangerous for health. Due to the importance of this matter, the European Union (EU) has established specific
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legislation. According to the Frame Regulation (EC) No. 1935/2004, all materials and articles intended to come in contact with foods should not transfer their constituents into food in quantities which could endanger human health or bring about unacceptable changes in composition or characteristics of foodstuffs. Directive 2002/72 includes a list of authorized substances that may be used in the manufacture of materials intended for food contact. According to the EU directive 85/572/EEC it is prescribed to perform migration tests in defined food simulants. The simulants for non-alcoholic beverages like fruit or vegetable juices are water, distilled or equivalent quality (simulant A). If the food pH value is equal to or less than 4.5, then 3% acetic acid (w/v) (simulant B) is used. The directive 2002/72/EC accepts migration estimation as long as valid models based on scientific evidence can be applied. The prediction of migration can be an excellent tool to support legislating agencies to make regulatory decision and to help food and packaging industries during packaging formulations. This approach saves time, economic and human resources. Many papers have already referred the importance of valid mathematical models to predict chemical migration from packaging into foodstuffs (Begley et al., 2005; Begley, 1997; Brandsch, Mercea, Tosa, & Piringer, 2002; Duffy, Hearty, Mccarthy, & Gibney, 2007; Hamdani, Feigenbaum, & Vergnaud, 1997; Petersen, Trier, & Fabech, 2005; Stoffers et al., 2005) and to estimate exposure to food-packaging migrants (Duffy & Gibney, 2007; Vitrac & Leblanc, 2007; Vitrac, Challe, Leblanc, & Feigenbaum, 2007). Nevertheless there are still scarce data concerning the estimation of migration key parameters (diffusion coefficients and partition coefficients) in real foodstuffs, especially aqueous foodstuffs. We have carried some previous works regarding the prediction of migration in different meat products (Sanches Silva, Cruz Freire, Sendo´n Garcı´a, Franz, & Paseiro Losada, 2007a) and in spread chocolate, chocolate and margarines (Sanches Silva, Cruz Freire, Sendo´n Garcı´a, Franz, & Paseiro Losada, 2007b, in press-c). Regarding the migration studies in orange juice, Rodushkin and Magnusson (2005) have studied the transfer of aluminium from laminated paperboard packages and more recently ITX, a photoinitiator, has also been studied by Sagratini, Man˜es, Giardina´, and Pico (2006) and Sun, Chan, Lu, Lee, and Bloodworth (2007). The aim of this work was to study the migration of the model migrant 1,4-dyphenyl-1,3-butadiene (DPBD) from a packaging film into two aqueous foodstuffs, tomato ketchup and orange juice. Moreover, acetic acid and water were checked for their suitability as aqueous foodstuffs simulants. Parameters that influence migration phenomena were evaluated and the mechanism of the migration of chemicals into these two food items was discussed. Effective diffusion coefficients were calculated according to a proposed mathematical model that allows the migration prediction of DPBD in orange juice.
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2. Experimental 2.1. Chemicals, standards and samples Acetonitrile (ACN), ethanol, acetic acid and hexane were purchased from Merck (Darmstadt, Germany). Ultrapure water was prepared using a Milli-Q filter system (Millipore, Bedford, MA, USA). Diphenylbutadiene (DPBD) had a purity of 98% and it was supplied by Sigma–Aldrich (Steinheim, Germany). A primary stock solution of DPBD was prepared in ethanol (1.0 mg/ml). Intermediate standard solutions of DPBD were prepared, by dilution, (0.1–10.0 lg/ml) for the calibration curve. The calibration curve consisted of a plot of peak area against the concentration of the standard calibration solutions. Solutions were stored in a refrigerator (5 °C). Orange juice and tomato ketchup were kindly supplied by the Foodmigrosure Consortium (EU Foodmigrosure Project, 2003). 2.2. Polymeric films The film used was a candidate certified reference material (CRM) for specific migration testing. It is an LDPE film (thickness 444 lm; density 0.912 g/cm3) spiked with 1,4-diphenyl-1,3-butadiene (DPBD) (CAS No. 538-81-8, MW = 206.3) and was produced by Fraunhofer IVV (Freising, Germany) according to a defined and recognised protocol (Specific Migration EU project, 2000; O’Brien et al., 1997; Stoffers et al., 2004). The initial concentration of the migrant in the polymer (CP,0) was 121.4 mg kg1. This corresponds to an area related maximum migration value of 491.6 lg/dm2. 2.3. Migration tests Samples (tomato ketchup and orange juice) and simulants (water and acetic acid 3%) (10 mL) were put into contact with the plastic containing the DPBD inside a migration cell (one-side contact and 0.1 dm2 of surface). Orange juice was analysed at 3 different temperatures and tomato ketchup at 2 temperatures. Table 1 shows the storage conditions used. A total of 10 samples were prepared for each kinetic curve for each aqueous foodstuff and temperature. Kinetic curves were carried out by duplicate. Samples were prepared previous HPLC analysis as described below. Table 1 Migration tests conditions for orange juice and tomato ketchup Food item
Storage temperature (°C)
Test conditions
Orange juice
5 25 40 25 70
2, 1, 1, 1, 2,
Tomato ketchup
4, 2, 2, 2, 4,
10, 20, 30 d 4, 10, 20 d 4, 6, 10 d 4, 10, 20 d 8, 16, 24 h
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Simulants migration tests were carried out at 40 °C for 10 days, also by duplicate and injected directly in the HPLC–DAD.
Table 3 Results of the tests carried out to understand the mechanism of migration of DPBD from LDPE films into orange juice Test
Description
DPBD concentration (mg/L)
1 2
Whole orange juice Orange juice after centrifugation, it means orange juice without coarse insoluble solids Orange juice centrifuged and filtered by 0.5 lm filter,it means orange juice without practically all insoluble solids Orange juice after hexane extraction, it means without organic substances extractable by hexane Water with benzene (approx. 0.08%) Water with hexane (approx. 0.04%) Solid residue after centrifugation dispersed in water
1.53 0.61
2.4. Samples extraction Orange juice and tomato ketchup samples (10 mL) were extracted with 2 20 mL of hexane and centrifuged at 3000 rpm (1036g) for 5 min. Then, the organic phase was separated by centrifugation and supernatants were pooled and evaporated in a rotary evaporator. The residue was dissolved with 10 mL of ACN. Previous HPLC–DAD analysis, solutions were filtered (Sendo´n, Sanches Silva, & Paseiro, 2004). 2.5. HPLC–UV conditions The HPLC system (Hewlett-Packard, Waldbronn, Germany) was fitted with a HP1100 quaternary pump, a degassing device, an autosampler, a column thermostatting system and a diode array UV detector. The detector was continuously performing a scan in the range 190–400 nm. The wavelengths used for diphenylbutadiene quantification was 330 nm, which corresponds to its highest absorbance peaks in UV scanning. The analysis was performed using acetonitrile (ACN) and water as mobile phase. The solvents gradient is shown in Table 2. The HP ChemStation chromatographic software was used for data acquisition. Chromatographic separation was performed with a Kromasil 100 C18 (15 cm 0.4 cm I.D., 5 lm particle size) (Teknokroma, Barcelona, Spain) at 30 °C. The flow-rate was 1.0 mL/ min and the injection volume was 50 lL. Diphenylbutadiene was identified by comparison of its retention time and UV spectra with those of an injected pure standard using the same HPLC conditions. 2.6. Tests to understand the migration mechanism of DPBD in orange juice These tests were carried out in hermetically closed centrifuge tubes. A small piece of film spiked with DPBD (1 2.5 cm) was immersed in the different matrices for 36 h at 70 °C. After this period, the plastic films were removed and 1 mL of the extract was diluted with 1 mL of acetonitrile. The solutions were then filtered prior to HPLC analysis. The tests conducted were summarized in Table 3.
Table 2 Solvents gradient of HPLC method Time (min)
Acetonitrile (%)
Water (%)
0 2 17 30
65 65 100 100
35 35 0 0
3
4 5 6 7
0.10
0.68 0.02 0.01 0.29
2.7. Mathematical models Eq. (1) (Crank, 1975; Han, Selke, Downes, & Harte, 2003) is commonly used to calculate key parameters of migration (diffusion and partition coefficients). " # 1 X M F;t 2að1 þ aÞ Dq2n t ¼1 exp ð1Þ 1 þ a þ a2 q2n M F;1 L2p n¼1 where MF,t is migrant amount in food at time t (lg); MF,1 is migrant amount in food at equilibrium (lg); a is the mass ratio of migrant in food to that in packaging film at equilibrium; D is the diffusion coefficient (cm2/s); Lp is the thickness of packaging film (cm); qn is the positive roots of the equation tan qn = a qn; t is the migration time (s). In the present work, diffusion coefficients were calculated using the simplest Eq. (2) (Crank, 1975) because Eq. (1) would require a very large number of roots. " # s 1=2 s M F;t 2 ¼ ð1 þ aÞ 1 e a erfc 2 a M F;1 ð2Þ Dt with s ¼ 2 Lp This equation also is recommended by FDA to model the sorption, at a fixed temperature, of any substances in plastic (FDA Guidance for Industry, 2006). In our case, D is an effective diffusion coefficient for the whole polymer-orange juice system. In this way a simplified but pragmatic mathematical model can be applied. Experimental data for orange juice and tomato ketchup were fitted to Eq. (2), by nonlinear regression, with commercial software (Solver of Microsoft Excel 2003). The root of the mean-square error % (RMSE(%)) was calculated using Eq. (3). This measure the fit between experimental and estimated data (Helmroth, Dekker, & Hankemeier, 2002):
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RMSEð%Þ ¼
1 M P;0 rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 XN 2 ððM F;t Þexperimental;i ðM F;t Þpredicted;i Þ i¼1 N 100 ð3Þ
where N is the number of experimental points per migration curve; i is the number of observations; MP,0 is the initial amount of the migrant in the polymer (lg). 3. Results and discussion
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Migration test were also carried out in 3% acetic acid and water at 40 °C for 10 days and results revealed there was no migration of DPBD from the same film. Tomato ketchup results are in agreement with those found for aqueous simulants. These findings can be explained by the high lipophilicity of DPBD which leads to negligible migration which is below the analytical detection limit. On the other hand, DPBD has migrated into orange juice with the highest DPBD concentration at 30 lg/dm2 obtained at 25 °C after 20 days of food/plastic contact. This means acetic acid and water may be appropriate simulants for tomato ketchup but not for orange juice.
3.1. DPBD migration in simulants, orange juice and tomato ketchup
3.2. Tests to understand DPBD migration in orange juice
The extraction procedure has been validated previously for orange juice and the recovery at 1 mg/kg was 85.2% (Sendo´n et al., 2004). Fig. 1 shows a typical chromatogram of an orange juice sample with DPBD as a result of foodstuff-plastic contact. In the present paper, tomato ketchup has been extracted with the same method as orange juice. Recovery has been checked using the standard addition procedure. At 1 mg/kg, the recovery was 86.78%. Migration of DPBD in tomato ketchup was not detected at 25 °C (DL = 3 lg/dm2). Accelerated migration tests were carried out at more severe conditions of temperature (70 °C) in tomato ketchup and migration was also not found.
In order to understand the migration mechanism of DPBD in orange juice (a representative beverage which is typically cloudy and not a clear liquid) we have carried out different rapid accelerated migration experiments at 70 °C for 36 h (Table 3). From tests 1, 2 and 3, we concluded that migration decreases as the quantity of insoluble solids is lowered in orange juice, without coarse insoluble solids migration decreases 60% and when orange juice is filtered through 0.45 lm then the decrease is 93%. This means that the presence of solids in the juice is the main and almost only factor responsible for detectable DPBD migration into orange juice. Because orange juice has a very small ‘‘fat” content (0.2% or less) (USDA database, 2006) and in order to study
Fig. 1. HPLC chromatogram of an orange juice sample after contact with PE-plastic film additivated with DPBD.
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the influence of this parameter in the migration process, three other tests were carried out (test 4, 5 and 6). Test 4 shows that substances extractable by hexane (its equivalent to fat content) play, in principle, an important role in the migration phenomenon, in orange juice without ‘‘fat” migration decreases 56%. However, it is important to stress that when orange juice is extracted with hexane the structure of orange juice is clearly modified, therefore the influence of substances extracted with hexane from orange juice should be target of study in the future. On the other hand, it is known that dissolved organic matter (DOM) in water increases the solubility of hydrophobic organic chemicals (Akkanen, Lyytika¨inen, Tuikka, & Kukkonen, 2005; Hunchak-Kariouk, Schweitzer, & Suffet, 1997). In order to test both the influence of DOM in the migration of DPBD to aqueous solutions and the effect of remaining hexane in orange juice after extraction, both an aliphatic (hexane) and an aromatic (benzene) molecules were added to water and migration test were carried out (tests 5 and 6). Results showed that migration was increased (0.01–0.02 mg/L) against water migration (n.d.), but it is insignificant comparing with the migration into orange juice. Therefore, DOM only is not a key parameter for the explanation of the migration of DPBD in orange juice. It seems that ‘‘fat” content linked with insoluble solids are the main factor to explain the DPBD migration into orange juice. Test 7 has given an interesting results because this kind of ‘‘new aqueous simulant” constitute by coarse insoluble solids separated by centrifugation from orange juice and dispersed in water showed a high migration (0.29 mg/L) against water (n.d.). It seems clear that insoluble solids are the main parameter that influence in the migration of DPBD in orange juice, probably it is powered by the presence of ‘‘fat” substances in the orange juice. Our results are in agreement with the recent work published by Sagratini et al. (2006) on the migration of isopropyl thioxanthone (ITX, photoinitiator) from packaging to foodstuffs. They attributed the migration of lipophilic ITX in milk to the presence of fat. Whereas the migration of ITX in orange juice was caused by the juice fibers which interact with the compound. 3.3. Mathematical models and determination of key parameters The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1 at 5, 25 and 40 °C, respectively. Taking into account that the diffusion coefficients in the polyethylene film for DPBD would be much lower and typically at 40 °C in the range of 1 108 cm2 s1 (Stoffers, 2004) the migration speed limiting step occurs in the orange juice at diffusion rate which is 3–4 order lower than in the polyethylene film. Again this can only be explained when
Fig. 2. Experimental and predicted migration values of DPBD into orange juice at 5, 25 and 40 °C.
solids in the otherwise liquid matrix dominate the migration process. More specifically, the explanation for this remarkable effect of a slowing down of the migration process of DPBD in orange juice can be found in the combination of two mass transport processes: (1) the transport from the plastic film to the aqueous phase and then (2) the adsorption and further absorption of the DPBD from the aqueous medium by insoluble solids which may be the slowest process. Another reason may be due to the direct mass transport of DPBD from the packaging to the insoluble solids may occur but this appears rather unlikely. Low RMSE(%) were found at the three temperatures (0.2, 0.7 and 0.5% at 5, 25 and 40 °C, respectively), showing that there is a good correlation between experimental and estimated migration values (Fig. 2). This indicates that this model can be used to predict DPBD migration into orange juice. 4. Concluding remarks In the present study, the migration of DPBD from PE films was studied in two aqueous foodstuffs, tomato ketchup and orange juice. Results showed that migration was negligible for tomato ketchup but not for orange juice. According to our results, the official EU food simulants A and B for migration tests are not suitable for orange juice and other high fiber products. Leaching of chemicals into cloudy juices and clear beverages should be considered differently. Migration of DPBD into orange juice is due to the presence of insoluble solids that concentrate DPBD from the aqueous phase of orange juice in which DPBD is very low soluble. Effective diffusion coefficients of DPBD into orange juice were calculated using a mathematical modelling based on Fick’s second Law. The effective diffusion coefficients of DPBD determined in the polymer-orange juice system were 2.9 1012, 3.7 1012, and 7.5 1012 cm2 s1 at 5, 25 and 40 °C, respectively, about
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3–4 orders of magnitude less than the in LDPE film (Stoffers, 2004). Acknowledgments The study was financially supported by EU Contract No. QLK1-CT2002-2390, Foodmigrosure and the Xunta de Galicia (Project No. PGIDIT05TAL20301PR). The Foodmigrosure Project is financially supported by the European Commission, under the Thematic Programme Quality of life and Management of Living Resources, Key Action 1 on Food, Nutrition and Health. The conclusions are the sole responsibility of the authors and do not represent the opinion of the European Commission. Authors are grateful to the ‘‘Ramo´n y Cajal” Program financed by the Ministry of Education of Spain and to the ‘‘Fundacßa˜o para a Cieˆncia e Tecnologia”, Portugal, for the Postdoctoral fellowship of Ana Sanches Silva. The authors are grateful to Ms. Patricia Blanco Carro and Mr. Gonzalo Hermelo Vidal for their excellent technical assistance. References Akkanen, J., Lyytika¨inen, M., Tuikka, A., & Kukkonen, J. (2005). Dissolved organic matter in pore water of freshwater sediments: Effects of separation procedure on quantity, quality and functionality. Chemosphere, 60(11), 1608–1615. Begley, T., Castle, L., Feigenbaum, A., Franz, R., Hinrichs, K., Lickly, T., et al. (2005). Evaluation of migration models that might be used in support of regulations for food-contact plastics. Food Additives and Contaminants, 22(1), 73–90. Begley, T. H. (1997). Methods and approaches used by FDA to evaluate the safety of packaging. Food Additives and Contaminants, 14(6–7), 545–553. Brandsch, J., Mercea, P., Tosa, V., & Piringer, O. (2002). Migration modeling as a tool for quality assurance of food packaging. Food Additives and Contaminants, 19(Suppl.), 29–41. Crank, J. (1975). The mathematics of diffusion (2nd ed.). Oxford: Clarendon, pp. 44–68. Duffy, E., & Gibney, M. J. (2007). Use of food-consumption database with packaging information to estimate exposure to food-packaging migrants: Expoxidized soybean oil and styrene monomer. Food Additives and Contaminants, 24(2), 216–225. Duffy, E., Hearty, A. P., Mccarthy, S., & Gibney, M. J. (2007). Estimation of exposure to food packaging materials. 3.: Development of consumption factors and food-type distribution factors from data collected on Irish children. Food Additives and Contaminants, 24(1), 63–74. EU directive 85/572/EEC laying down the list of simulants to be used for testing migration of constituents of plastic materials and articles intended to come into contact with foodstuffs. EU Official Journal L372 of 31.12.1985; 14–21. EU directive 2002/72/EC relating to plastics materials and articles intended to come into contact with foodstuffs. EU Official Journal L220 of 15.08.2002; 18–55. EU Project ‘‘Specific Migration” Certified reference materials for specific migration testing of plastics for food packaging needed by industry and enforcement laboratories. Project supported by European Commission under Contract No. (G6RD-CT-2000-00411). EU Project ‘‘Foodmigrosure” (Modelling migration from plastics into foodstuffs as a novel and cost efficient tool for estimation of consumer (plastic-food) for estimation of exposure from food contact materials).
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