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Food Additives & Contaminants Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfac19
Migration testing of plastics and microwave‐active materials for high‐temperature food‐use applications a
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L. Castle , S. M. Jickells , J. Gilbert & N. Harrison
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Food Safety Directorate, Food Science Laboratory , Ministry of Agriculture, Fisheries and Food , Colney Lane, Norwich, NR4 7UQ, UK b
Food Science Division I , Ergon House, 17 Smith Square, London, SW1P 3JR, UK Published online: 10 Jan 2009.
To cite this article: L. Castle , S. M. Jickells , J. Gilbert & N. Harrison (1990) Migration testing of plastics and microwave‐active materials for high‐temperature food‐use applications, Food Additives & Contaminants, 7:6, 779-796, DOI: 10.1080/02652039009373940 To link to this article: http://dx.doi.org/10.1080/02652039009373940
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FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, NO. 6, 7 7 9 - 7 9 6
Migration testing of plastics and microwave-active materials for high-temperature food-use applications L. CASTLE†, S. M. JICKELLS†, J. GILBERT† and N. HARRISON‡
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† Ministry of Agriculture, Fisheries and Food, Food Safety Directorate, Food Science Laboratory, Colney Lane, Norwich NR4 7UQ, UK ‡ Food Science Division I, Ergon House, 17 Smith Square, London SW1P 3JR, UK (Received 7 February 1990; revised 3 April 1990; accepted 10 April 1990) Temperatures have been measured using a fluoro-optic probe at the food/container or food/packaging interfaces as appropriate, for a range of foods heated in either a microwave or a conventional oven. Reheating ready-prepared foods packaged in plastics pouches, trays or dishes in the microwave oven, according to the manufacturers' instructions, resulted in temperatures in the range 61-121° C. Microwave-active materials (susceptors) in contact with ready-prepared foods frequently reached local spot temperatures above 200°C. For foods cooked in a microwave oven according to published recipes, temperatures from 91°C to 200°C were recorded, whilst similar temperatures (92-194°C) were attained in a conventional oven, but over longer periods of time. These measurements form the basis for proposing high-temperature test conditions to be used in statutory methods for examining compliance with specific and overall migration limits for plastics materials. The testing conditions proposed depend on the intended use of the plastic—for microwave oven use for aqueous foods, for all lidding materials, and for reheating of foods, testing would only be required with aqueous simulants for 1 h at 100°C; for unspecified microwave oven use, testing with olive oil would be required for 30 min at 150 C; and for unspecified use in a conventional oven testing with olive oil would be required for 2 h at 175 °C. For microwave-active materials, it is proposed that testing is carried out in the microwave oven using a novel semi-solid simulant comprising olive oil and water absorbed onto an inert support of diatomaceous earth. The testing in this instance is carried out with the simulant instead of food in a package and heating in the microwave oven at 600 W for 4 min for every 100 g of simulant employed. There is an option in every case to test for migration using real foods rather than simulants if it can be demonstrated that results using simulants are unrepresentative of those for foods. The proposed testing conditions were validated as being realistic by measurement of the specific migration of various components from different plastics into foods under actual conditions of use and comparing with migration into simulants. Migration of plasticizers from PVC and VC/VDC copolymer films was monitored for both microwave reheating and cooking of foods. Total oligomer concentrations were measured from poly(ethylene terephthalate) (PET) trays, and volatile aromatics from thermoset polyester trays, using both types of container in microwave and conventional ovens. For microwave-active materials, total PET oligomer concentrations as well as those of an individual oligomer (cyclic trimer) were used as migration indicators into foods and simulants. Keywords: Migration, plastics, susceptors, microwave-active packaging, test conditions, microwave ovens, conventional ovens, high-temperature migration testing, cooking, reheating, semi-solid food simulant.
Introduction Within the European Community there is a slow but progressive move towards the adoption by member states of harmonized standards and testing of food contact © Crown Copyright 1990
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materials. These standards include a limit on the migration of total constituents of food contact plastics (overall migration) of 10 mg/dm2 or 60 mg/kg (EEC 1990) as well as specific migration limits for substances from a positive list of monomers and other starting substances. A list of plastics additives is also in preparation (McGuinness 1986). Test conditions for the determination of overall migration are specified in Directive 82/71 I/EEC (EEC 1982) together with specifications for food simulants, the choice of the appropriate simulant being based on a given classification of foods (EEC 1985). Test conditions are stipulated in Directive 82/71 I/EEC for most situations, depending on the intended temperature of use and contact time. However, for a period of contact of less than 2 h at a temperature exceeding 121 °C the test conditions are allowed to be 'in accordance with national laws' (EEC 1982, Rossi 1988a,b). In this paper we report work that was undertaken to establish the temperatures actually experienced at the food contact interface between the food and container when foods are cooked or reheated in either a microwave or a conventional oven. These data are then used as the basis for proposing temperature and exposure times for testing materials and articles to check for compliance with overall and specific migration limits. Food contact materials can be used at elevated temperatures in the home either in the form of flexible films for covering foods to prevent drying-out in microwave ovens, or as rigid plastics cookware articles, both mainly being applications using home-prepared foods. In the form of packaging for convenience foods (principally precooked frozen foods), plastics trays and dishes are used for reheating (in microwave or conventional ovens) according to manufacturers' instructions. Additionally, there are microwave-active materials used in applications requiring browning of foods, again mainly being used according to specific instructions, and which are not yet subject to EEC proposals. A wide range of foods and extremes of temperature might be experienced in the home-use situation, compared with the pre-packaged foods where the suitability of the package for the food and the temperature conditions likely to be experienced are established by the manufacturer. Both types of situations must, however, be allowed for in proposing conditions for high temperature testing of food contact materials. Plastics films are widely recommended in cookbooks and oven manufacturers' instructions for use in microwave cookery to cover foods during heating to prevent the surface drying out. They are suggested specifically for use during baking (piercing the film to allow steam to escape), reheating plates of precooked food, wrapping whole large vegetables during cooking and for covering frozen dishes during reheating direct from the freezer. A number of popular cookery books give recipes where foods are cooked in direct contact with film. These foods range from meat, poultry, fish and vegetable dishes to steamed puddings, cakes and biscuits. Testing of PVC film ('cling film') plasticized with di-(2-ethylhexyl)adipate (DEHA) was carried out in the UK in 1986 (Startin et al. 1987a) for a variety of foods which were either cooked or reheated in microwave ovens. An assessment of the DEHA migration from these films in such situations led to the recommendation that this type of film should not in future be used under any circumstances in conventional ovens, nor should it be used for lining of dishes or wrapping of foods in a microwave oven (Ministry of Agriculture, Fisheries and Food 1987). Reheating of foods covered with film was, however, found to be acceptable, as migration was significantly lower in this instance. Appropriate labelling, with instructions for the
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consumer, for use of plasticized films in microwave cooking was subsequently agreed. Work was also undertaken on vinyl chloride/vinylidene chloride (VC/VDC) copolymer film plasticized with acetyltributyl citrate (ATBC), which is sold as being suitable for microwave use. Levels of ATBC plasticizer used in this film were lower than that of DEHA used in PVC film, and the migration into foods was consequently lower (Castle etal. 1988a). Both the use of PVC plasticized film for covering foods during reheating and of the VC/VDC film for use in cooking in a microwave oven need to be covered by any testing regime. Very recently microwave-'active' packaging materials, commonly called susceptors, have been introduced for use in the microwave oven for the browning of foods such as pizzas, potato chips, popcorn and pastries. These materials have a construction consisting of plastic (typically PET food contact layer), aluminium and adhesive on a paperboard substrate. The susceptor functions by absorbing microwave energy and generating high local temperatures (in excess of 200°C). This high temperature can, on occasion, lead to some disruption of the PET (crazing) and charring of the adhesive and paperboard layers with the release of pyrolysis volatiles (Booker and Friese 1989). It was clear that testing of these active materials would have to be undertaken in a microwave oven, and that conventional food simulants would not be suitable. In this paper we address this question and propose a novel simulant specifically for testing of microwave-active materials. It is important that any testing regime, whether for films, susceptors or rigid cookware articles, should be demonstrated to give migration results that are realistic in relation to the migration that would take place under actual conditions of use. Although it can be accepted that testing should be more severe than normal use, testing should nevertheless not be so extreme as to eliminate materials which can be demonstrated to give acceptable migration levels in normal use. Statutory testing of materials will normally measure overall or total migration which cannot easily be measured in real foods. However, if for a number of different species from a number of different plastics it can be demonstrated that migration into the appropriate simulant under the proposed testing conditions gives migration levels broadly equivalent to those into the foods, it can be assumed that the same should apply to levels of overall migration. Therefore, in this paper in support of the proposed testing conditions, we have chosen a number of materials and carried out measurements of specific migration both into food and into the EC-specified simulants. Plasticizer migration has been measured from flexible films; oligomers have been measured from PET rigid articles and susceptors; and benzene, an example of a volatile aromatic species, has been measured from thermoset polyester articles. Finally, in order to gain an appreciation of the likely effect of the introduction of the proposed testing regime, some overall migration measurements have been made for typical plastics materials intended for use in microwave and conventional ovens. Experimental
Materials Cookware articles designated specifically for microwave or conventional oven use were obtained as retail purchases. The PVC film was a representative sample
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of 'Freshcling', which on analysis was established as containing 10% DEHA plasticizer together with polymeric plasticizer and epoxidized soyabean oil. The VC/VDC copolymer film used was a retail sample labelled as being suitable for microwave use which on analysis was found to contain 4·5% ATBC plasticizer. Food samples were either foods sold fresh, which had no prior contact with plastics materials, or were ready-prepared foods prepackaged in plastics with instructions for microwave or conventional oven reheating. Samples of susceptor boards were supplied by Waddingtons Cartons Ltd (Leeds, UK) and the susceptor wrapping film was a retail purchase. Temperature measurements of foods All temperature measurements in foods were made using a fibre-optic probe (ASEA model F100, Takada Electric Mfg Co. Tokyo, Japan) equipped with an FTP-3 sensor capable of recording temperatures over the range 0-200°C. The probe was inserted through a hole drilled in the top of the microwave oven (Sharp Carousel Model R-7400) such that the probe could be placed in the food and temperature monitored whilst the oven turntable was in operation. In the case of flexible films the plastic was punctured so that the tip of the probe could be placed adjacent to the surface of the food at the plastics interface. With rigid plastic cookware articles the probe was taped in position (Scotch electrical tape), as far as possible maintaining the probe tip in the food and at the interface position on the inner surface of the plastic. For measurements using microwave-active materials the probe tip was similarly taped in position on the PET surface, either inserted through the simulant and taped, or taped in place and then subsequently covered with the appropriate food. Temperature profiles during cooking were recorded continuously on a chart recorder. At the end of the cooking/reheating period, plus standing time where appropriate, the temperature probe was removed from the static position and quickly used to test for 'hot spots' at other locations at the food/packaging interface. All temperature measurements were carried out with a minimum of three cooking/reheating experiments with the probe placed at different positions on the interface. Migration into food simulants Migration from plasticized films into aqueous and fatty food simulants was carried out by total immersion of the film in the simulant and also by single-sided contact in a test cell. Results for immersion experiments are calculated for the area of film employed (for example for 10 X 10 cm = 1 dm2) and not for the total area immersed (which in this example would be 2 dm 2 ). For the total immersion experiments the film (1 ·0 dm 2 ) was held on a cruciform support (Rossi 1981) sandwiching the film between pieces of aluminium mesh to ensure complete exposure to the simulant without the film folding back upon itself. The aqueous simulant (100 ml), contained in a 250 ml Pyrex glass boiling tube fitted with a ground-glass stopper, was initially maintained at 100° C in a fan circulating oven, with the plastic attached in place on the holder, suspended above, but not in contact with, the simulant. When both simulant and plastic had attained equilibrium at 100° C the test sample was lowered into the simulant and the glass stopper clipped into position. After 1 h at 100°C the tube was removed from the oven, and the test sample removed quickly from the hot simulant which was retained for subsequent analysis.
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For single-sided contact the film (2Ό dm 2 ) was clamped in position in a PIRA stainless-steel migration test cell (supplied by PIRA, Leatherhead, UK) and was placed to preheat in a fan-circulating oven at 121 °C. The oil simulant (100 ml) contained in a beaker was preheated in the oven, and when both simulant and cell had reached operating temperature the simulant was poured directly through the fill-inlet of the cell for the migration test. After 1 h the cell was removed from the oven and, after allowing the cell to cool, the simulant was poured from the cell for analysis. For testing of the PET trays, preheated olive oil (30 ± 1 g) was poured into the tray which was then held at 150°C for 30 min or 175°C for 2 h as appropriate, before removal of the hot oil by pipette. For testing with 3% acetic acid solution the PET tray containing preheated simulant was placed in a shallow bath of water in a sealed glass container, so that there was no loss by evaporation during testing and the whole system could be maintained at 100°C in a fan-circulating oven. For testing thermoset polyester cookware articles for benzene, small plaques of the material of an accurately known weight (5-7 g) and of known surface area (about 0-3 dm 2 ) were placed in 24 ml glass vials together with olive oil (15 g). The vials were sealed with PTFE-faced septa and heated for 30 min at 150° C or 2 h at 175°C as appropriate. At the end of the migration experiment the vials were cooled at - 20°C for 30 min, the plaques removed and aliquots of the oil (2 g) were placed in 24 ml vials and sealed with PTFE-faced septa. Migration into semi-solid simulant The semi-solid simulant was prepared by mixing overnight, (Tumble-mixer, Pascal Engineering Co. Ltd) Celite 545 (40% w/w), olive oil (25% w/w) and distilled water (35% w/w) to form a friable solid of uniform consistency. Samples (1 -0 g) of the simulant were analysed for water content (weight loss on drying) and oil content (chloroform extraction) to ensure homogeneity. Simulant of weight equal to that of the food it was intended to replace was spread as a compressed uniform layer over a predetermined area of the susceptor. Heating was carried out in the centre of the microwave oven at a power setting of 600 W for times recommended for the respective foods. After carrying out the migration test the simulant was tipped from the susceptor, which was gently tapped. Charred simulant which adhered to the susceptor was not removed for analysis as there was a risk of removing particulate PET which would artificially inflate the migration values. DEHA plasticizer migration The analysis of DEHA plasticizer in foods was carried out using the stable isotope dilution GC/MS method previously described (Startin et al. 1987b). For the analysis of DEHA in aqueous simulant, the simulant (100 ml) contained within the original migration tube (immersion experiments) or in a separating funnel (PIRA single-sided test cell experiments) was extracted with chloroform (2 ml) containing C20 or C24 hydrocarbon as internal standard (25 /*g/ml). The organic layer was directly analysed by GC with flame ionization detection using a Carlo Erba 4160 capillary GC operated isothermally at 220°C in a split mode (50:1). The 25 m x 0-22 mm i.d. fused silica CPSIL 5CB—0-12/xm film thickness, capillary column (Chrompack, London) was operated at a carrier gas (hydrogen) flowrate of 2 ml/min. Quantification was on the basis of the peak area of DEHA relative to that of the internal standard.
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A TBC plasticizer migration The analysis of ATBC plasticizer in foods was carried out using the stable isotope dilution GC/MS procedure previously described (Castle et al. 1988b). For the analysis of the aqueous simulant the extraction and GC method was identical to that described above for DEHA plasticizer. Total PET oligomers migration The analysis of total levels of PET oligomers in foods was carried out by hydrolysis of the oligomers to terephthalic acid, followed by methylation and quantification as dimethyl terephthalate by isotope dilution to GC/MS using a deuterated internal standard as previously described (Castle et al. 1989). The olive oil simulant was similarly analysed for oligomers by taking an aliquot (3 g), adding internal standard (10 μ\ of a 20 mg/ml solution of isophthalic acid in aqueous potassium hydroxide), followed by 0 · 2 Μ methanolic potassium hydroxide (10 ml) and hydrolysing for 4-5 h at 65 °C. Boron trifluoride etherate (2 g) was added and the reaction continued for a further 5 h at 65°C. The reaction mixture was quenched with water (50 ml), partitioned into diethyl ether (40 ml) and washed with a further portion of water (50 ml) followed by half-saturated sodium sulphate solution (50 ml). The organic phase was dried over sodium sulphate, the ether removed and the remaining oily residue was partitioned between acetonitrile (50 ml) and hexane (50 ml). The acetonitrile layer was washed with two further portions of hexane (2 χ 50 ml) and evaporated to around 1 ml. This solution was then analysed by capillary GC using a 25 m χ 0·22 mm i.d. CPSIL 5CB column, temperature programmed from 120°C (held for 1 min), at 3°C /min to 130°C (held for 5 min) and then raising to 200°C to bake out the column. Injections (1 μ\) were in a split mode (25:1) with a hydrogen carrier gas at 2 ml/min. PET oligomers were quantified (as dimethyl terephthalate) using peak area ratios against dimethylisophthalate internal standard. Calibration curves were constructed from the reaction and analysis of isophthalic acid and terephthalic acid standards added to olive oil. Headspace analysis of benzene Benzene was analysed in foods and in olive oil simulant by headspace GC/MS as previously described (Jickells et al. 1990). PET cyclic trimer migration For the semi-solid food simulant a subsample (30 g) was taken for analysis, to which concentrated hydrochloric acid (1 ml) was added together with 1:1 acetone/hexane (150 ml). After homogenization with an Ultra Turrax blender for 5 min, the supernatant was decanted and the solid residue extracted twice with fresh solvent (2 x 150 ml). The extract was dried overnight over sodium sulphate, evaporated to dryness and the weight of the fat residue recorded. A sample of the fat (0-25 g) in hexane (1 ml) was loaded onto a hexane preconditioned Bond-Elut silica cartridge column (500 mg size), which was subsequently eluted with 5% ethyl acetate in hexane (6 ml), followed by 15% ethyl acetate in hexane (3 ml). Elution of the fraction containing the PET cyclic trimer was with 50% ethyl acetate in hexane (3 ml) into a 4 ml glass vial. The extract was evaporated to dryness under a gentle stream of nitrogen, redissolved in 0-50ml of 60% aqueous acetonitrile, centrifuged and transferred to a clean vial. Analysis was by HPLC with UV detection (241 nm) using two 100 mm x 3 mm i.d. ODS 2 cartridge columns in series
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with a 10mmCi8 guard column. The solvent flowrate of 0·3 ml/min was maintained isocratically with 3:1 acetonitrile/water for the analysis and then rapidly programmed to 9:1 acetonitrile/water to flush the column prior to the next analysis. Quantification was based on external standards of trimer spiked into the semi-solid simulant and carried through the method. The primary standard employed for calibration was a recrystallized fraction of a chloroform extract of PET. This standard was confirmed as cyclic trimer by mass spectrometry (chemical ionization mode) and was greater than 90% pure by 'H NMR and Chromatographie analysis. Results and discussion It has been demonstrated in this laboratory (S. Jickells, unpublished results) that, for a number of different plastics and for different chemical species, no quantitative effect on migration could be observed as a result of microwave energy over and above that expected from the heating effect alone. For the purposes of testing of food contact materials and articles it is therefore unnecessary to carry out migration tests in a microwave oven, and it is proposed that testing be carried out using conventional heating. This means that materials intended for microwave and conventional oven use can be tested using the same testing procedures, and this also avoids the particular difficulties associated with establishing reproducible conditions in a microwave oven. Unfortunately, microwave-active materials are a special case where the rapid generation of high local temperatures can only be achieved in a microwave oven, and test conditions for these materials have therefore been considered separately. Two distinct uses of plastics for high-temperature applications were identified: (1) those used in the home which were sold as empty containers or as films, which might be exposed to a range of conditions and could be subjected to extremes of use in terms of temperatures, times of cooking and food type; (2) those used as packaging of, for example, oven-ready foods where the designated application was well-defined, both in terms of the type of food and the conditions of use. It was clear that it would be unreasonable to have a single test condition covering both situations as this would be unnecessarily severe for prepackaged food applications. It was also clear that if different levels of testing, dependent on usage, were proposed, these would need to be intrinsically linked to requirements of labelling of the articles for their intended application. For testing, it is therefore proposed that for articles sold containing foods, the temperature of the test would depend on the temperature actually reached during cooking, when the article was used according to the manufacturers' instructions. Home-use ovenable materials and cookware Temperature measurements. Temperatures measured at the food/plastics contact interface for foods prepared in the home using microwavable materials and articles are shown in table 1. Most foods are predominantly aqueous and final temperatures achieved did not generally exceed 100°C. These observations are consistent with other reports (Ahvenainen et al. 1989). There were, however, notable cases of foods with high fat or high sugar content where temperatures of the order of 150°C were attained and, in exceptional instances such as well-cooked bacon, where the hot fat exposed the cookware to temperatures above 200°C.
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L. Castle et al. Table 1. Temperatures of foods during cooking in a microwave oven.
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Food type Sweetcorn cob Brussel sprouts Spinach Lasagne sauce Lasagne complete Stuffed peppers Onions (fried) Fruit sauce Butterscotch Cheesecake base Cheesecake complete Pâté Chicken (ca 1-3 kg) Bacon (one rasher) Meringue Peanut brittle Marmalade
Cooking conditions Wrapped in film Wrapped in film Wrapped in film Cooked in open bowl Cooked in serving dish Stood on buttered dish Cooked in open bowl Cooked in open bowl Cooked in jug Cooked in dish Cooked in dish Cooked in shallow dish Roasted uncovered on dish Cooked on open grid Cooked to browning Cooked in open bowl Cooked in open bowl Cooked in open bowl
Time (min)
Power
4 4 4 5 10 12 3 5 5 2 15 40
600 600 600 600 600 600 600 600 600 600 600 600 450 600 600 600 600 600
37 2 3-4 20 24 70
(W)
Max temp. (°C) 102 100 100 91 101 96 106 101 123 121 106 100 106 155
200 + 150 150 116
Proposed test conditions. Based on these observations, materials that are not expected to contact food intimately, but which may be exposed to aqueous condensate, should be tested according to conditions set by the EC for materials not expected to exceed 121 °C in use. These conditions are also applicable where contact with aqueous foods only is prescribed by labelling. For purposes of testing materials and articles for suitability for unrestricted use in a microwave oven, an upper temperature of 150°C was selected from the data in table 1 as being a more severe temperature than was generally experienced by plastics cookware, but not so severe as to be an unreasonable test temperature. A time of 30 min was selected as the period for testing at 150°C, again this time being seen as a more severe test than for most normal applications (which were in the range 4-12 min), but not unreasonable in view of identified examples of uses where contact times from 40 to 70 min were required (for example in the cooking of pâté and marmalade, respectively). Testing would be with olive oil. For unrestricted use in both microwave and conventional ovens testing using olive oil at 175°C for 2 h is proposed. These conditions are stringent, but were chosen to align with regulations already in existence elsewhere (Anon 1976) and thus to avoid the necessity for separate testing regimes for the UK. Migration results. It is of interest to assess how plastics materials and articles that are used currently, perform under the test conditions proposed here, and how well the test migration results correlate with migration levels in real foods. This section examines these aspects. The comparison of test results with results for real foods has not employed the reduction factors available in Directive 85/572/EEC (EEC 1985) which allows for the aggressive nature of simulants compared with real foods. Migration from plasticized films PVC films for sale in the UK should be labelled as being unsuitable for use in
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Table 2. Results comparing migration from plastics into foods under actual conditions of use with those for simulants under proposed or specified (EEC, 1982) testing conditions. (β) DEHA plasticizer from PVC 'Freshcling' film Migration
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Food Pizza Curry Pasty Potato Meal
Conditions Reheat-microwave Reheat-microwave Reheat-microwave Reheat-microwave Reheat-microwave
mg/kg 27-0 0-9 7-0 2-6 0-6
Migration 2
mg/dm
Simulant
1-35 0-08 0-47 0-22 0-06
Water Water Water Water Water
2
Conditions
mg/kg
mg/dm
100°C-60 min 100°C-60 min 100°C-60 min 100°C-60 min 100°C-60 min
0-5 0-5 0-5 0-5 0-5
0-05 0-05 0-05 0-05 0-05
(b) A TBC plasticizer from VCj VDC copolymer film Migration Food Soup Pizza Meal Bread Cakes Biscuits
Conditions Cover-microwave Reheat-microwave Reheat-microwave Direct-microwave Direct-microwave Direct-microwave
mg/kg
Migration
mg/dm2
Simulant
Conditions
mg/kg
mg/dm2
0-1 4-9 0-6 0-6 1-7 5-1
Water Water Water Olive oil Olive oil Olive oil
100 C-60min 100°C-60 min lQ0°C-60 min 121°C-30min 121°C-30min 121°C-30min
1-4 1-4 1-4
0-15 0-15 0-15 6-2 6-2 6-2
0-4 35-0 29-9 22-0 22-3 79-8
(c) Total PET oligomers from PET cookware Migration
Migration Food Lasagne Sausage Apple Cherries Lasagne Curry
Conditions 204 C-80 min 204°C-60 min 204°C-40 min 204°C-40 min Microwave, 3 min Microwave, 3 min
mg/kg 1-1 0-4 0-2 0-1 0-1 0-1
mg/dm2 0-3 0-1
Food Additives & Contaminants Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tfac19
Migration testing of plastics and microwave‐active materials for high‐temperature food‐use applications a
a
a
L. Castle , S. M. Jickells , J. Gilbert & N. Harrison
b
a
Food Safety Directorate, Food Science Laboratory , Ministry of Agriculture, Fisheries and Food , Colney Lane, Norwich, NR4 7UQ, UK b
Food Science Division I , Ergon House, 17 Smith Square, London, SW1P 3JR, UK Published online: 10 Jan 2009.
To cite this article: L. Castle , S. M. Jickells , J. Gilbert & N. Harrison (1990) Migration testing of plastics and microwave‐active materials for high‐temperature food‐use applications, Food Additives & Contaminants, 7:6, 779-796, DOI: 10.1080/02652039009373940 To link to this article: http://dx.doi.org/10.1080/02652039009373940
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FOOD ADDITIVES AND CONTAMINANTS, 1990, VOL. 7, NO. 6, 7 7 9 - 7 9 6
Migration testing of plastics and microwave-active materials for high-temperature food-use applications L. CASTLE†, S. M. JICKELLS†, J. GILBERT† and N. HARRISON‡
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† Ministry of Agriculture, Fisheries and Food, Food Safety Directorate, Food Science Laboratory, Colney Lane, Norwich NR4 7UQ, UK ‡ Food Science Division I, Ergon House, 17 Smith Square, London SW1P 3JR, UK (Received 7 February 1990; revised 3 April 1990; accepted 10 April 1990) Temperatures have been measured using a fluoro-optic probe at the food/container or food/packaging interfaces as appropriate, for a range of foods heated in either a microwave or a conventional oven. Reheating ready-prepared foods packaged in plastics pouches, trays or dishes in the microwave oven, according to the manufacturers' instructions, resulted in temperatures in the range 61-121° C. Microwave-active materials (susceptors) in contact with ready-prepared foods frequently reached local spot temperatures above 200°C. For foods cooked in a microwave oven according to published recipes, temperatures from 91°C to 200°C were recorded, whilst similar temperatures (92-194°C) were attained in a conventional oven, but over longer periods of time. These measurements form the basis for proposing high-temperature test conditions to be used in statutory methods for examining compliance with specific and overall migration limits for plastics materials. The testing conditions proposed depend on the intended use of the plastic—for microwave oven use for aqueous foods, for all lidding materials, and for reheating of foods, testing would only be required with aqueous simulants for 1 h at 100°C; for unspecified microwave oven use, testing with olive oil would be required for 30 min at 150 C; and for unspecified use in a conventional oven testing with olive oil would be required for 2 h at 175 °C. For microwave-active materials, it is proposed that testing is carried out in the microwave oven using a novel semi-solid simulant comprising olive oil and water absorbed onto an inert support of diatomaceous earth. The testing in this instance is carried out with the simulant instead of food in a package and heating in the microwave oven at 600 W for 4 min for every 100 g of simulant employed. There is an option in every case to test for migration using real foods rather than simulants if it can be demonstrated that results using simulants are unrepresentative of those for foods. The proposed testing conditions were validated as being realistic by measurement of the specific migration of various components from different plastics into foods under actual conditions of use and comparing with migration into simulants. Migration of plasticizers from PVC and VC/VDC copolymer films was monitored for both microwave reheating and cooking of foods. Total oligomer concentrations were measured from poly(ethylene terephthalate) (PET) trays, and volatile aromatics from thermoset polyester trays, using both types of container in microwave and conventional ovens. For microwave-active materials, total PET oligomer concentrations as well as those of an individual oligomer (cyclic trimer) were used as migration indicators into foods and simulants. Keywords: Migration, plastics, susceptors, microwave-active packaging, test conditions, microwave ovens, conventional ovens, high-temperature migration testing, cooking, reheating, semi-solid food simulant.
Introduction Within the European Community there is a slow but progressive move towards the adoption by member states of harmonized standards and testing of food contact © Crown Copyright 1990
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materials. These standards include a limit on the migration of total constituents of food contact plastics (overall migration) of 10 mg/dm2 or 60 mg/kg (EEC 1990) as well as specific migration limits for substances from a positive list of monomers and other starting substances. A list of plastics additives is also in preparation (McGuinness 1986). Test conditions for the determination of overall migration are specified in Directive 82/71 I/EEC (EEC 1982) together with specifications for food simulants, the choice of the appropriate simulant being based on a given classification of foods (EEC 1985). Test conditions are stipulated in Directive 82/71 I/EEC for most situations, depending on the intended temperature of use and contact time. However, for a period of contact of less than 2 h at a temperature exceeding 121 °C the test conditions are allowed to be 'in accordance with national laws' (EEC 1982, Rossi 1988a,b). In this paper we report work that was undertaken to establish the temperatures actually experienced at the food contact interface between the food and container when foods are cooked or reheated in either a microwave or a conventional oven. These data are then used as the basis for proposing temperature and exposure times for testing materials and articles to check for compliance with overall and specific migration limits. Food contact materials can be used at elevated temperatures in the home either in the form of flexible films for covering foods to prevent drying-out in microwave ovens, or as rigid plastics cookware articles, both mainly being applications using home-prepared foods. In the form of packaging for convenience foods (principally precooked frozen foods), plastics trays and dishes are used for reheating (in microwave or conventional ovens) according to manufacturers' instructions. Additionally, there are microwave-active materials used in applications requiring browning of foods, again mainly being used according to specific instructions, and which are not yet subject to EEC proposals. A wide range of foods and extremes of temperature might be experienced in the home-use situation, compared with the pre-packaged foods where the suitability of the package for the food and the temperature conditions likely to be experienced are established by the manufacturer. Both types of situations must, however, be allowed for in proposing conditions for high temperature testing of food contact materials. Plastics films are widely recommended in cookbooks and oven manufacturers' instructions for use in microwave cookery to cover foods during heating to prevent the surface drying out. They are suggested specifically for use during baking (piercing the film to allow steam to escape), reheating plates of precooked food, wrapping whole large vegetables during cooking and for covering frozen dishes during reheating direct from the freezer. A number of popular cookery books give recipes where foods are cooked in direct contact with film. These foods range from meat, poultry, fish and vegetable dishes to steamed puddings, cakes and biscuits. Testing of PVC film ('cling film') plasticized with di-(2-ethylhexyl)adipate (DEHA) was carried out in the UK in 1986 (Startin et al. 1987a) for a variety of foods which were either cooked or reheated in microwave ovens. An assessment of the DEHA migration from these films in such situations led to the recommendation that this type of film should not in future be used under any circumstances in conventional ovens, nor should it be used for lining of dishes or wrapping of foods in a microwave oven (Ministry of Agriculture, Fisheries and Food 1987). Reheating of foods covered with film was, however, found to be acceptable, as migration was significantly lower in this instance. Appropriate labelling, with instructions for the
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consumer, for use of plasticized films in microwave cooking was subsequently agreed. Work was also undertaken on vinyl chloride/vinylidene chloride (VC/VDC) copolymer film plasticized with acetyltributyl citrate (ATBC), which is sold as being suitable for microwave use. Levels of ATBC plasticizer used in this film were lower than that of DEHA used in PVC film, and the migration into foods was consequently lower (Castle etal. 1988a). Both the use of PVC plasticized film for covering foods during reheating and of the VC/VDC film for use in cooking in a microwave oven need to be covered by any testing regime. Very recently microwave-'active' packaging materials, commonly called susceptors, have been introduced for use in the microwave oven for the browning of foods such as pizzas, potato chips, popcorn and pastries. These materials have a construction consisting of plastic (typically PET food contact layer), aluminium and adhesive on a paperboard substrate. The susceptor functions by absorbing microwave energy and generating high local temperatures (in excess of 200°C). This high temperature can, on occasion, lead to some disruption of the PET (crazing) and charring of the adhesive and paperboard layers with the release of pyrolysis volatiles (Booker and Friese 1989). It was clear that testing of these active materials would have to be undertaken in a microwave oven, and that conventional food simulants would not be suitable. In this paper we address this question and propose a novel simulant specifically for testing of microwave-active materials. It is important that any testing regime, whether for films, susceptors or rigid cookware articles, should be demonstrated to give migration results that are realistic in relation to the migration that would take place under actual conditions of use. Although it can be accepted that testing should be more severe than normal use, testing should nevertheless not be so extreme as to eliminate materials which can be demonstrated to give acceptable migration levels in normal use. Statutory testing of materials will normally measure overall or total migration which cannot easily be measured in real foods. However, if for a number of different species from a number of different plastics it can be demonstrated that migration into the appropriate simulant under the proposed testing conditions gives migration levels broadly equivalent to those into the foods, it can be assumed that the same should apply to levels of overall migration. Therefore, in this paper in support of the proposed testing conditions, we have chosen a number of materials and carried out measurements of specific migration both into food and into the EC-specified simulants. Plasticizer migration has been measured from flexible films; oligomers have been measured from PET rigid articles and susceptors; and benzene, an example of a volatile aromatic species, has been measured from thermoset polyester articles. Finally, in order to gain an appreciation of the likely effect of the introduction of the proposed testing regime, some overall migration measurements have been made for typical plastics materials intended for use in microwave and conventional ovens. Experimental
Materials Cookware articles designated specifically for microwave or conventional oven use were obtained as retail purchases. The PVC film was a representative sample
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of 'Freshcling', which on analysis was established as containing 10% DEHA plasticizer together with polymeric plasticizer and epoxidized soyabean oil. The VC/VDC copolymer film used was a retail sample labelled as being suitable for microwave use which on analysis was found to contain 4·5% ATBC plasticizer. Food samples were either foods sold fresh, which had no prior contact with plastics materials, or were ready-prepared foods prepackaged in plastics with instructions for microwave or conventional oven reheating. Samples of susceptor boards were supplied by Waddingtons Cartons Ltd (Leeds, UK) and the susceptor wrapping film was a retail purchase. Temperature measurements of foods All temperature measurements in foods were made using a fibre-optic probe (ASEA model F100, Takada Electric Mfg Co. Tokyo, Japan) equipped with an FTP-3 sensor capable of recording temperatures over the range 0-200°C. The probe was inserted through a hole drilled in the top of the microwave oven (Sharp Carousel Model R-7400) such that the probe could be placed in the food and temperature monitored whilst the oven turntable was in operation. In the case of flexible films the plastic was punctured so that the tip of the probe could be placed adjacent to the surface of the food at the plastics interface. With rigid plastic cookware articles the probe was taped in position (Scotch electrical tape), as far as possible maintaining the probe tip in the food and at the interface position on the inner surface of the plastic. For measurements using microwave-active materials the probe tip was similarly taped in position on the PET surface, either inserted through the simulant and taped, or taped in place and then subsequently covered with the appropriate food. Temperature profiles during cooking were recorded continuously on a chart recorder. At the end of the cooking/reheating period, plus standing time where appropriate, the temperature probe was removed from the static position and quickly used to test for 'hot spots' at other locations at the food/packaging interface. All temperature measurements were carried out with a minimum of three cooking/reheating experiments with the probe placed at different positions on the interface. Migration into food simulants Migration from plasticized films into aqueous and fatty food simulants was carried out by total immersion of the film in the simulant and also by single-sided contact in a test cell. Results for immersion experiments are calculated for the area of film employed (for example for 10 X 10 cm = 1 dm2) and not for the total area immersed (which in this example would be 2 dm 2 ). For the total immersion experiments the film (1 ·0 dm 2 ) was held on a cruciform support (Rossi 1981) sandwiching the film between pieces of aluminium mesh to ensure complete exposure to the simulant without the film folding back upon itself. The aqueous simulant (100 ml), contained in a 250 ml Pyrex glass boiling tube fitted with a ground-glass stopper, was initially maintained at 100° C in a fan circulating oven, with the plastic attached in place on the holder, suspended above, but not in contact with, the simulant. When both simulant and plastic had attained equilibrium at 100° C the test sample was lowered into the simulant and the glass stopper clipped into position. After 1 h at 100°C the tube was removed from the oven, and the test sample removed quickly from the hot simulant which was retained for subsequent analysis.
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For single-sided contact the film (2Ό dm 2 ) was clamped in position in a PIRA stainless-steel migration test cell (supplied by PIRA, Leatherhead, UK) and was placed to preheat in a fan-circulating oven at 121 °C. The oil simulant (100 ml) contained in a beaker was preheated in the oven, and when both simulant and cell had reached operating temperature the simulant was poured directly through the fill-inlet of the cell for the migration test. After 1 h the cell was removed from the oven and, after allowing the cell to cool, the simulant was poured from the cell for analysis. For testing of the PET trays, preheated olive oil (30 ± 1 g) was poured into the tray which was then held at 150°C for 30 min or 175°C for 2 h as appropriate, before removal of the hot oil by pipette. For testing with 3% acetic acid solution the PET tray containing preheated simulant was placed in a shallow bath of water in a sealed glass container, so that there was no loss by evaporation during testing and the whole system could be maintained at 100°C in a fan-circulating oven. For testing thermoset polyester cookware articles for benzene, small plaques of the material of an accurately known weight (5-7 g) and of known surface area (about 0-3 dm 2 ) were placed in 24 ml glass vials together with olive oil (15 g). The vials were sealed with PTFE-faced septa and heated for 30 min at 150° C or 2 h at 175°C as appropriate. At the end of the migration experiment the vials were cooled at - 20°C for 30 min, the plaques removed and aliquots of the oil (2 g) were placed in 24 ml vials and sealed with PTFE-faced septa. Migration into semi-solid simulant The semi-solid simulant was prepared by mixing overnight, (Tumble-mixer, Pascal Engineering Co. Ltd) Celite 545 (40% w/w), olive oil (25% w/w) and distilled water (35% w/w) to form a friable solid of uniform consistency. Samples (1 -0 g) of the simulant were analysed for water content (weight loss on drying) and oil content (chloroform extraction) to ensure homogeneity. Simulant of weight equal to that of the food it was intended to replace was spread as a compressed uniform layer over a predetermined area of the susceptor. Heating was carried out in the centre of the microwave oven at a power setting of 600 W for times recommended for the respective foods. After carrying out the migration test the simulant was tipped from the susceptor, which was gently tapped. Charred simulant which adhered to the susceptor was not removed for analysis as there was a risk of removing particulate PET which would artificially inflate the migration values. DEHA plasticizer migration The analysis of DEHA plasticizer in foods was carried out using the stable isotope dilution GC/MS method previously described (Startin et al. 1987b). For the analysis of DEHA in aqueous simulant, the simulant (100 ml) contained within the original migration tube (immersion experiments) or in a separating funnel (PIRA single-sided test cell experiments) was extracted with chloroform (2 ml) containing C20 or C24 hydrocarbon as internal standard (25 /*g/ml). The organic layer was directly analysed by GC with flame ionization detection using a Carlo Erba 4160 capillary GC operated isothermally at 220°C in a split mode (50:1). The 25 m x 0-22 mm i.d. fused silica CPSIL 5CB—0-12/xm film thickness, capillary column (Chrompack, London) was operated at a carrier gas (hydrogen) flowrate of 2 ml/min. Quantification was on the basis of the peak area of DEHA relative to that of the internal standard.
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A TBC plasticizer migration The analysis of ATBC plasticizer in foods was carried out using the stable isotope dilution GC/MS procedure previously described (Castle et al. 1988b). For the analysis of the aqueous simulant the extraction and GC method was identical to that described above for DEHA plasticizer. Total PET oligomers migration The analysis of total levels of PET oligomers in foods was carried out by hydrolysis of the oligomers to terephthalic acid, followed by methylation and quantification as dimethyl terephthalate by isotope dilution to GC/MS using a deuterated internal standard as previously described (Castle et al. 1989). The olive oil simulant was similarly analysed for oligomers by taking an aliquot (3 g), adding internal standard (10 μ\ of a 20 mg/ml solution of isophthalic acid in aqueous potassium hydroxide), followed by 0 · 2 Μ methanolic potassium hydroxide (10 ml) and hydrolysing for 4-5 h at 65 °C. Boron trifluoride etherate (2 g) was added and the reaction continued for a further 5 h at 65°C. The reaction mixture was quenched with water (50 ml), partitioned into diethyl ether (40 ml) and washed with a further portion of water (50 ml) followed by half-saturated sodium sulphate solution (50 ml). The organic phase was dried over sodium sulphate, the ether removed and the remaining oily residue was partitioned between acetonitrile (50 ml) and hexane (50 ml). The acetonitrile layer was washed with two further portions of hexane (2 χ 50 ml) and evaporated to around 1 ml. This solution was then analysed by capillary GC using a 25 m χ 0·22 mm i.d. CPSIL 5CB column, temperature programmed from 120°C (held for 1 min), at 3°C /min to 130°C (held for 5 min) and then raising to 200°C to bake out the column. Injections (1 μ\) were in a split mode (25:1) with a hydrogen carrier gas at 2 ml/min. PET oligomers were quantified (as dimethyl terephthalate) using peak area ratios against dimethylisophthalate internal standard. Calibration curves were constructed from the reaction and analysis of isophthalic acid and terephthalic acid standards added to olive oil. Headspace analysis of benzene Benzene was analysed in foods and in olive oil simulant by headspace GC/MS as previously described (Jickells et al. 1990). PET cyclic trimer migration For the semi-solid food simulant a subsample (30 g) was taken for analysis, to which concentrated hydrochloric acid (1 ml) was added together with 1:1 acetone/hexane (150 ml). After homogenization with an Ultra Turrax blender for 5 min, the supernatant was decanted and the solid residue extracted twice with fresh solvent (2 x 150 ml). The extract was dried overnight over sodium sulphate, evaporated to dryness and the weight of the fat residue recorded. A sample of the fat (0-25 g) in hexane (1 ml) was loaded onto a hexane preconditioned Bond-Elut silica cartridge column (500 mg size), which was subsequently eluted with 5% ethyl acetate in hexane (6 ml), followed by 15% ethyl acetate in hexane (3 ml). Elution of the fraction containing the PET cyclic trimer was with 50% ethyl acetate in hexane (3 ml) into a 4 ml glass vial. The extract was evaporated to dryness under a gentle stream of nitrogen, redissolved in 0-50ml of 60% aqueous acetonitrile, centrifuged and transferred to a clean vial. Analysis was by HPLC with UV detection (241 nm) using two 100 mm x 3 mm i.d. ODS 2 cartridge columns in series
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with a 10mmCi8 guard column. The solvent flowrate of 0·3 ml/min was maintained isocratically with 3:1 acetonitrile/water for the analysis and then rapidly programmed to 9:1 acetonitrile/water to flush the column prior to the next analysis. Quantification was based on external standards of trimer spiked into the semi-solid simulant and carried through the method. The primary standard employed for calibration was a recrystallized fraction of a chloroform extract of PET. This standard was confirmed as cyclic trimer by mass spectrometry (chemical ionization mode) and was greater than 90% pure by 'H NMR and Chromatographie analysis. Results and discussion It has been demonstrated in this laboratory (S. Jickells, unpublished results) that, for a number of different plastics and for different chemical species, no quantitative effect on migration could be observed as a result of microwave energy over and above that expected from the heating effect alone. For the purposes of testing of food contact materials and articles it is therefore unnecessary to carry out migration tests in a microwave oven, and it is proposed that testing be carried out using conventional heating. This means that materials intended for microwave and conventional oven use can be tested using the same testing procedures, and this also avoids the particular difficulties associated with establishing reproducible conditions in a microwave oven. Unfortunately, microwave-active materials are a special case where the rapid generation of high local temperatures can only be achieved in a microwave oven, and test conditions for these materials have therefore been considered separately. Two distinct uses of plastics for high-temperature applications were identified: (1) those used in the home which were sold as empty containers or as films, which might be exposed to a range of conditions and could be subjected to extremes of use in terms of temperatures, times of cooking and food type; (2) those used as packaging of, for example, oven-ready foods where the designated application was well-defined, both in terms of the type of food and the conditions of use. It was clear that it would be unreasonable to have a single test condition covering both situations as this would be unnecessarily severe for prepackaged food applications. It was also clear that if different levels of testing, dependent on usage, were proposed, these would need to be intrinsically linked to requirements of labelling of the articles for their intended application. For testing, it is therefore proposed that for articles sold containing foods, the temperature of the test would depend on the temperature actually reached during cooking, when the article was used according to the manufacturers' instructions. Home-use ovenable materials and cookware Temperature measurements. Temperatures measured at the food/plastics contact interface for foods prepared in the home using microwavable materials and articles are shown in table 1. Most foods are predominantly aqueous and final temperatures achieved did not generally exceed 100°C. These observations are consistent with other reports (Ahvenainen et al. 1989). There were, however, notable cases of foods with high fat or high sugar content where temperatures of the order of 150°C were attained and, in exceptional instances such as well-cooked bacon, where the hot fat exposed the cookware to temperatures above 200°C.
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Food type Sweetcorn cob Brussel sprouts Spinach Lasagne sauce Lasagne complete Stuffed peppers Onions (fried) Fruit sauce Butterscotch Cheesecake base Cheesecake complete Pâté Chicken (ca 1-3 kg) Bacon (one rasher) Meringue Peanut brittle Marmalade
Cooking conditions Wrapped in film Wrapped in film Wrapped in film Cooked in open bowl Cooked in serving dish Stood on buttered dish Cooked in open bowl Cooked in open bowl Cooked in jug Cooked in dish Cooked in dish Cooked in shallow dish Roasted uncovered on dish Cooked on open grid Cooked to browning Cooked in open bowl Cooked in open bowl Cooked in open bowl
Time (min)
Power
4 4 4 5 10 12 3 5 5 2 15 40
600 600 600 600 600 600 600 600 600 600 600 600 450 600 600 600 600 600
37 2 3-4 20 24 70
(W)
Max temp. (°C) 102 100 100 91 101 96 106 101 123 121 106 100 106 155
200 + 150 150 116
Proposed test conditions. Based on these observations, materials that are not expected to contact food intimately, but which may be exposed to aqueous condensate, should be tested according to conditions set by the EC for materials not expected to exceed 121 °C in use. These conditions are also applicable where contact with aqueous foods only is prescribed by labelling. For purposes of testing materials and articles for suitability for unrestricted use in a microwave oven, an upper temperature of 150°C was selected from the data in table 1 as being a more severe temperature than was generally experienced by plastics cookware, but not so severe as to be an unreasonable test temperature. A time of 30 min was selected as the period for testing at 150°C, again this time being seen as a more severe test than for most normal applications (which were in the range 4-12 min), but not unreasonable in view of identified examples of uses where contact times from 40 to 70 min were required (for example in the cooking of pâté and marmalade, respectively). Testing would be with olive oil. For unrestricted use in both microwave and conventional ovens testing using olive oil at 175°C for 2 h is proposed. These conditions are stringent, but were chosen to align with regulations already in existence elsewhere (Anon 1976) and thus to avoid the necessity for separate testing regimes for the UK. Migration results. It is of interest to assess how plastics materials and articles that are used currently, perform under the test conditions proposed here, and how well the test migration results correlate with migration levels in real foods. This section examines these aspects. The comparison of test results with results for real foods has not employed the reduction factors available in Directive 85/572/EEC (EEC 1985) which allows for the aggressive nature of simulants compared with real foods. Migration from plasticized films PVC films for sale in the UK should be labelled as being unsuitable for use in
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Table 2. Results comparing migration from plastics into foods under actual conditions of use with those for simulants under proposed or specified (EEC, 1982) testing conditions. (β) DEHA plasticizer from PVC 'Freshcling' film Migration
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Food Pizza Curry Pasty Potato Meal
Conditions Reheat-microwave Reheat-microwave Reheat-microwave Reheat-microwave Reheat-microwave
mg/kg 27-0 0-9 7-0 2-6 0-6
Migration 2
mg/dm
Simulant
1-35 0-08 0-47 0-22 0-06
Water Water Water Water Water
2
Conditions
mg/kg
mg/dm
100°C-60 min 100°C-60 min 100°C-60 min 100°C-60 min 100°C-60 min
0-5 0-5 0-5 0-5 0-5
0-05 0-05 0-05 0-05 0-05
(b) A TBC plasticizer from VCj VDC copolymer film Migration Food Soup Pizza Meal Bread Cakes Biscuits
Conditions Cover-microwave Reheat-microwave Reheat-microwave Direct-microwave Direct-microwave Direct-microwave
mg/kg
Migration
mg/dm2
Simulant
Conditions
mg/kg
mg/dm2
0-1 4-9 0-6 0-6 1-7 5-1
Water Water Water Olive oil Olive oil Olive oil
100 C-60min 100°C-60 min lQ0°C-60 min 121°C-30min 121°C-30min 121°C-30min
1-4 1-4 1-4
0-15 0-15 0-15 6-2 6-2 6-2
0-4 35-0 29-9 22-0 22-3 79-8
(c) Total PET oligomers from PET cookware Migration
Migration Food Lasagne Sausage Apple Cherries Lasagne Curry
Conditions 204 C-80 min 204°C-60 min 204°C-40 min 204°C-40 min Microwave, 3 min Microwave, 3 min
mg/kg 1-1 0-4 0-2 0-1 0-1 0-1
mg/dm2 0-3 0-1
