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E. T. Contis et al. (Editors) Food Flavors: Formation, Analysis and Packaging Influences © 1998 Elsevier Science B.V. All rights reserved

759

Effect of microwave heating on the migration of dioctyladipate and acetyltributylcitrate plasticizers from food-grade PVC and PVDC/PVC films into ground meat. A.B. Badeka and M.G. Kontominas

Laboratory of Food Chemistry and Technology, Department of Chemistry, University of loannina, GR-45110, Greece.

Abstract Migration of dioctyladipate (DOA) and acetyltributylcitrate (ATBC) plasticizers from plasticized polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC/PVC) (Saran) films into ground meat of varying fat content (3%, 12%, 30% and 55%) has been studied. Meat samples were wrapped in PVC or Saran film and cooked for 0.5, 1, 1.5, 2, 2.5, 3, 4 min in a microwave oven on full power (~700W). The plasticizer migrating into meat was determined using an indirect GC method after saponification of the ester-type plasticizer (DOA or ATBC) and subsequent collection of the alcohol component of the ester, namely, 2-ethyl-lhexanol and 1-butanol, respectively. Migration was dependent on heating time, meat fat content and initial concentration of plasticizer in the film. The migration of plasticizer into meat did not reach equilibrium after heating for 4 min even in high fat content (55%) meat samples. Migration values of DOA and ATBC into 55% fat content meat samples after heating for 4 min was 846.0 mg/kg (14.7mg/dm2) and 95.1 mg/kg (2.5 mg/dm^) respectively.

1. INTRODUCTION

Microwaving is becoming an increasingly used process for the heating of foodstuffs in both the industrial and home sectors in Europe. The microwave oven is used for a variety of purposes such as cooking, baking, frying, defrosting, reheating, drying, enzyme inactivation, pasteurization, sterilization etc. [1-3]. Microwave processing offers several advantages over conventional heating methods. These advantages include speed of operation, energy savings, precise process control and faster start-up and shut-down times [1-3].

760 A variety of foods have been developed and modified over the past few years for the microwave market. Many of these food products are cooked with the packaging material (container or wrapping film) in the microwave oven. Such microwavable materials include plastics, paperboard and composites [4-8]. However, during cooking due to a significant increase in temperature, a variety of plastics additives contained in most packaging materials, i.e. plasticizers, antioxidants, stabilizers, residual monomers etc. may migrate from the packaging material into the food. This may result in the deterioration of food quality i.e. off-flavor and/or safety problems [9-12]. The migration of low molecular weight compounds from a polymeric material into a food-contacting phase is dependent on: the nature and thickness of the packaging material, the nature of the food in contact, initial concentration of the additive in the polymer, compatibility of the additive/polymer system, temperature, time of contact etc. [13-15] Polyvinylchloride (PVC) and polyvinyhdene chloride (PVCD)/PVC (Saran), films have found wide applications in the packaging of a large variety of foodstuffs. Also for covering foods during cooking in the microwave oven in order to prevent the drying out of the food surface and when baking dishes, reheating precooked meals and covering frozen dishes during reheating from the freezer. The most commonly used plasticizer for PVC is dioctyladipate (DOA) added at levels up to 40% (w/w), and for Saran it is acetyltributylcitrate (ATBC) added at levels up to 5% (w/w). There are several published studies dealing with the migration of plasticizers into different foods and/or food simulants during microwave heating [9, 11, 12, 15, 16-19]. All of them report equilibrium migration values. The present work involves a kinetic study of the migration of DOA and ATBC plasticizers from food grade PVC and PVDC/PVC (Saran) films respectively, into ground meat of varying fat content.

2. MATERIALS AND METHODS

2.1. Materials The PVC film used was MX-B LM, 15|im in thickness, containing 28.3% DOA (w/w) supplied by Borden, Chemical Division, N.Andover, Mass., USA. The Saran film used was 12|im in thickness containing 4.9% ATBC (w/w) supplied by Dow, Indianapolis, Ind., USA. Analytical grade DOA was purchased from Fluka (Buchs, Switzerland). Analytical grade ATBC was purchased from Unitex, Greensboro, N.C., USA. Analytical grade 2-ethyl-l-hexanol was purchased from Merck, Darmstadt, Germany. Analytical grade 1-butanol was purchased from Mallinckrodt, St. Louis, Mo., USA. Beef meat and fat were purchased locally.

761 2.2. Migration experiments Ground meat of 3% fat content was uniformly mixed with fat in a meat chopper so as to achieve meat samples of fat content 12%, 30% and 55%. Fat content was determined according to AOAC Soxhlet method [20]. Ground meat patties, approximately 40g in weight, were wrapped in PVC or Saran film and cooked for 0.5, 1, 1.5, 2, 2.5, 3 and 4 min in a microwave oven on full power (~700W). The total area of the film in contact with meat was 1.45dm2. All experiments were carried out in triplicate. For comparison purposes identical unwrapped samples (controls) were cooked in the microwave oven.

2.3. Analysis of DOA plasticizer The contaminated meat (~40g) was extracted in a Soxhlet apparatus with hexane for 6 h. After evaporation of hexane the residue was saponified with KOH 2N in methanol for 3 h. The volume of KOH 2N in methanol was dependent on meat fat content (8 mL/g fat). Thus DOA was decomposed to adipic acid and 2ethyl-1-hexanol. After saponification, methanol was evaporated in a rotoevaporator, the residue was acidified with HCl solution (1:1 v/v) and subjected to steam distillation until 200 mL of distillate had been collected. The distillate was extracted four times with 50 mL diethyl ether. The combined ether extracts were left overnight with 30 g anhydrous Na2S04. Diethyl ether was evaporated after separation from Na2S04. The residue was redissolved in CS2 and the CS2 solution was used to determine 2-ethyl-l-hexanol by GC using an appropriate standard curve. The recovery factor of the above method was obtained by addition of known amounts of DOA to ground meat samples and determination of the plasticizer content using the same procedure as for unknown samples.

2.4. Analysis of ATBC plasticizer The contaminated meat (~40g) was extracted in a Soxhlet apparatus with hexane for 6 h. After evaporation of hexane the residue was saponified with solid KOH for 7 min. The quantity of KOH was dependent on meat fat content (Ig/g fat). Thus ATBC was decomposed to citric acid and 1-butanol. After the saponification stage, the procedure followed was the same as that described above for DOA analysis. The recovery factor of the above method was obtained by addition of known amounts of ATBC to ground meat samples and determination of the plasticizer content using the same procedure as for unknown samples.

2.5. GC operational conditions The alcohol component of DOA, namely, 2-ethyl-l-hexanol, was determined under the following conditions: The GC unit was a Varian model 3700 GC equipped with a dual flame ionization detector. The column was of aluminum (1.90m long, 6.35mm o.d.) packed with 10% SE-30 stationary phase on Anachrom

762 ABS 60/80 Mesh. The temperatures used were: column, 165°C; injection port, 220°C; detector, 220°C. The alcohol component of ATBC, namely, 1-butanol, was determined under the following conditions: The GC unit was the same as that described above, the column was of stainless steel (Im long, 3.17mm o.d.) packed with 10% Carbowax 20 M on Supelcoport 80/100 Mesh. The temperatures used were: column, 65°C; injection port, 200°C; detector, 220°C.

3. RESULTS AND DISCUSSION

3.1. Migration of DOA Recovery factors of 74.5%, 74%, 84% and 82.3% for DOA into ground meat of 3%, 12%, 30% and 55% fat content were obtained respectively. The amounts of DOA migrated from PVC film into ground meat of varying fat content during microwave heating on full power (~700W) as a function of time are given in Figure 1. As shown in Figure 1 DOA migration into meat is time and fat content dependent. Migration of DOA into ground meat did not reach equilibrium after heating for 4 min even in high fat content (55%) meat samples (845.96 mg/kg or 23.5 mg/dm2). This value represents a 46.0% loss of the DOA plasticizer migrated from the PVC film into the ground meat sample.

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Time (min) Figure 1. Migration of DOA from PVC film into ground meat of fat content a) (A) 3%, b) (•) 12%, c) (•) 30% and d) (•)55% during microwave heating on full power.

763 DOA was not detected in unwrapped (control) meat samples. The migration amount of DOA into ground meat of fat content 3%, 12%, 30% and 55% after heating for 4 min was 195.2 mg/kg (5.42 mg/dm^), 565.1 mg/kg (15.70 mg/dm^), 771.8 mg/kg (21.44 mg/dm2) and 846.0 mg/kg (23.50 mg/dm2) respectively. Bishop and Dye [9] reported an average migration value of 21.2mg DOA/20 mL vegetable oil (1060 mg/1) after 10 min of cooking in the microwave oven. No further details were given on the dimensions and thickness of the film used, power setting of the oven, or the plasticizer content of the film used. Our DOA migration value into meat of 55% fat content after heating for 4 min is comparable to the above mentioned value (1060 mg/1), given the differences in nature of the food product (fat content), time of heating, area of contact between the foodstuff and PVC film, temperature etc. Startin et al [19] studied the migration of DOA into a variety of food products during microwave cooking and reported values of 435 mg/kg for peanut biscuits, 351 mg/kg for pork spare ribs, 191 mg/kg for cakes and 3 mg/kg for carrots. The film contained 17.2% DOA while its thickness, contact area between film and food and the cooking time were not specified. It is clear that as the fat content of the food increases the migration amount of the plasticizer will also increase. Our migration values are generally higher than the above, a fact which can be attributed to differences in experimental conditions, area of the film used, percentage of the plasticizer in PVC film, fat content etc. Harrison [12] reported DOA migration values ranging from 146 to 435 mg/kg for fatty foods such as chicken (152 mg/kg), pork (351 mg/kg), trout (146 mg/kg) and peanut biscuits (435 mg/kg). No further details were given in this work so it is difficult to attempt comparison of these values to ours. Finally, Castle et al [16] studied the migration of DOA into foods during the "reheating" process in a microwave oven and reported values ranging from 27 mg/kg for pizza to 2.6 mg/kg for potatoes. The film used contained 10% DOA along with polymeric plasticizer. It is obvious that the migration amounts under the above mentioned experimental conditions are much lower than our migration values.

3.2. Migration of ATBC Recovery factors of 65.3%, 64.7%, 66.4% and 65% for ATBC into ground meat of fat content 3%, 12%, 30% and 55% were obtained respectively. The amounts of ATBC migrated from Saran film into ground meat of varying fat content during microwave heating on full power (~700W) as a function of time are given in Figure 2. As shown in Figure 2 ATBC migration into meat is time and fat content dependent. Migration of ATBC into ground meat did not reach equilibrium after heating for 4 min even in high fat content (55%) meat samples (95.1 mg/kg or 2.50 mg/dm2). This value represents a 21.5% loss of the ATBC plasticizer which migrated from Saran film into the ground meat sample. ATBC was not detected in control meat samples. Furthermore ATBC was not detected in meat samples of fat content 3%. The migration amount of ATBC into

764 ground meat of fat content 12%, 30% and 55% after heating for 4 min was 40.2 mg/kg (1.06mg/dm2), 72.4 mg/kg (1.91 mg/dm2) and 95.1mg/kg (2.50 mg/dm2) respectively.

Time (min)

Figure 2. Migration of ATBC from Saran film into ground meat of fat content a) (A) 12%, b) (•)30% and c) (•)55% during microwave heating on full power.

Health and Reilly [18] reported that the migration of ATBC into poultry products during microwave cooking was time dependent, reaching equilibrium after 8 min of cooking (0.834 mg butanol/g). This value is much higher than our value 0.05 mg/g for meat of fat content 55% heated for 4 min at full power. This can be attributed to differences in time of heating and fat content of the foodstuffs used in the two studies. Health and Reilly also showed that an increased fat content of the food resulted in increased migration of the plasticizer. Castle et al [17] studied the migration of ATBC into various foods and reported values ranging from 79.8 mg/kg for peanut biscuits to 0.9 ^glhg for Brussels sprouts. The migration value of 79.8 mg/kg for peanut biscuits coirelates well with our value of approximately 95.1 mg/kg obtained for meat of fat content 55% after 4 min of microwave heating at full power. Finally, Castle et al [16] reported a migration value for ATBC of 79.9 mg/kg for high fat biscuits and 35.0 mg/kg for pizza under reheating conditions in a microwave oven. Both these values are of the same order of magnitude as our values, given the differences in experimental conditions between the two studies. What should be stressed is that under present experimental conditions the DOA migration is higher than the upper limit for global migration (60 mg/kg or

765 10 mg/dm^) set by the E.U. even for meat samples of low fat content. The ATBC migration is higher than the upper limit for global migration only for meat samples of high fat content. The present results indicate that PVC film should not be used in direct contact with foodstuffs in the microwave oven while Saran film may be used with appropriate caution in the microwave oven avoiding direct contact of high fat foodstuffs with the film. Further study on migration of the two plasticizers (DOA, ATBC) from cling films (PVC, Saran) into solid foodstuffs (pizza, sausage etc.) is in progress.

4. REFERENCES

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