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Chapter 8
Food Contact Materials: Characterization of Migrants Rafael Paseiro-Cerrato,*,1,2 Lowri DeJager,1 and Timothy H. Begley1 1U.S.
FDA, Center for Food Safety and Applied Nutrition, 5001 Campus Drive, College Park, Maryland 20740, United States 2Joint Institute for Food Safety and Applied Nutrition (JIFSAN), University of Maryland, College Park, Maryland 20742, United States *E-mail:
[email protected] Food contact materials (FCMs) may contain substances that can migrate into food. To help ensure consumers’ safety, analysis of these substances (migrants) should be performed, including characterization of possible migrants in the FCMs, food, and/or food simulants. An introduction to the world of FCMs and analytical techniques used to analyze them will be briefly described in this chapter. The reader will become familiarized with FCMs and the science behind their analysis.
© 2019 American Chemical Society Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
Introduction Food contact materials (FCMs) have become a part of daily life for millions of consumers. They can be seen almost everywhere in society: grocery stores, at home, movie theatres, restaurants, etc. They may be manufactured from paper, plastics, ceramics, as well as other materials and have various shapes and functions. Food packaging is usually used to protect food from environmental agents, such as air and light, and increase shelf life.
Migration from FCMs When FCMs are placed in contact with food, there is a process of mass transfer, commonly called migration, that cannot be completely avoided. Most FCMs are polymeric materials, formed from the chemical reactions of starting substances commonly called monomers. Additives are also used to protect and impart certain properties to FCMs. In addition, other contaminants may be present or created during the manufacturing process and become part of the FCMs. Some of these chemicals may migrate into food and, if not controlled, may pose a potential food safety issue. Therefore, several countries have regulations on FCMs to protect consumer health. Regulatory Background In the United States, FCMs are regulated under the Federal Food and Drug and Cosmetic Act, which requires U.S. Food and Drug Administration (FDA) approval of any food additives, including food contact substances used in the manufacturing of FCMs, before being placed on the market. There are three processes for receiving approval from the FDA for the use of an FCM: the food additive petition process (FAP), the food contact notification process (FCNP), and the threshold of regulation (TOR) exemption request. The FAP results in a listing in the Code of Federal Regulations (CFR) Title 21, Parts 170–199 (1), which contains several parts for FCMs. Some examples of these parts include: -
Part 175: Adhesives and general components of coatings; Part 176: Paper and paperboard components; and Part 177: Polymers.
In the CFR, important definitions pertaining to FCMs can be found, such as definitions of a food additive and the principle of general recognition of safety. Some parts of the CFR provide technical information regarding to material specifications as well as specifications for substances that are authorized for the manufacturing of FCMs. Some FCMs have use limitations and end tests requirements that they must comply with prior to introduction into the market. End test requirements (specifications/limitations) are intended to ensure that the material manufactured is consistent with the material that was evaluated under the 124 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
food additive petition. If the regulations in the CFR are followed, the material(s) or food contact substances can be marketed in the United States. Another process for marketing FCMs was established in 1997 when the FDA Modernization Act created the FCNP (1), which has two main differences from the FAP in the CFR: it is a faster procedure (maximum of 120 days) and the authorization is specific to the filer of the notification. In an FCNP, the notifier files a food contact notification consisting of administrative, environmental, toxicology, and chemistry information supporting the safety of the FCMs under its intended use conditions. Once the FDA has reviewed the food contact notification and determined they do not object to the use of FCMs, the FCMs can be placed in the market. In the TOR exemption request, it may be used if a food additive results in a dietary concentration at or below 0.5 ppb and the substance has not been shown to be a carcinogen. For more specific information on the TOR exemption, see 21 CFR 170.39 (1). Under the European legislation, the legislation frame for FCMs is Regulation (EC) 1935/2004 (2). A crucial part of this regulation for FCMs is article 3. Briefly, this article states that materials or articles in contact with food shall comply with good manufacturing practices (see Commission Regulation (EC) 2023/2006 (3)) and will not transfer constituents in quantities which could endanger human health or make unacceptable changes in food composition or deterioration of organoleptic characteristics. On the other hand, in the EU there are specific measures for the following materials: -
Plastic materials (Commission Regulation (EU) 10/2011 (4)); Recycled plastic materials; Active and intelligent materials; Ceramics; and Regenerated cellulose film.
One of the most relevant EU regulations for FCMs is Commission Regulation (EU) 10/2011 (4), in which positive lists of substances that can be used in the manufacturing of plastic FCMs are included. In addition, this legislation sets specific migration limits based on toxicological studies. Food Simulants and Contact Time-Temperature Conditions In order to accurately determine mass transfer between FCMs and the food, the exact amount of migrant that is present in the food must be measured. Analyzing food for FCMs or other analytes is complex and challenging. Food is extremely diverse and is often a complex mixture of fats, carbohydrates, and protein. Analysis of trace concentrations of analytes in foods generally requires expensive instrumentation that, in many cases, is not sensitive or selective enough for migration testing. As a result, most legislation allows the use of food simulants as a model to predict migration. Food simulants are supposed to represent the physical and chemical properties of foods, and they can be used to simulate migration of a substance from FCMs to food while simplifying the analysis of the resulting matrix. The choice of food simulant is based on chemical properties of 125 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
the food of interest. For example, 50% ethanol may be used as food simulant to model migration into milk. Presented in Table 1 are examples of food simulants. The time and temperatures used for migration experiments should be based on the extreme storage times and temperature conditions that the FCMs would be exposed to. In the United States, the most commonly used conditions are 40 °C for 10 days. Some examples of time-temperature protocols based on FDA guidance for industry are (5): -
High temperature, heat sterilized, or retorted: 121 °C for 2 h + 10 days at 40 °C; Boiling water sterilized: 100 °C for 2 h + 10 days at 40 °C; Hot filled or pasteurized above 66 °C: 100 °C for 30 min + 10 days at 40 °C; Hot filled or pasteurized below 66 °C: 66 °C for 30 min + 10 days at 40 °C; Room temperature filled and stored: 24, 48, 120, and 240 h (10 days) at 40 °C; Frozen or refrigerated storage; ready-prepared foods intended to be reheated in container at time of use: 100 °C for 2 h; and Irradiation: No protocols. Consult.
Table 1. Food Simulants under Commission Regulation (EU) 10/2011. Source: Data from ref (4)
Analysis of FCMs, Food, and Food Simulants The goal of the migration test is to determine the concentration of migrants transferred from the FCMs into the food. When producing the FCMs, manufacturers use monomers and additives. Most of these substances are known and consequently relatively “easy” to analyze as long as analytical standards are available. However, during the manufacturing process, side reactions may occur and non-intentionally added substances (NIAS) may be present in the final material. As the name indicates, these substances are not intentionally added to 126 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
the FCMs, but they may be present and migrate into food. These substances also need to be evaluated to ensure consumer safety and regulatory compliance. We will discuss strategies for characterization, including identification of unknown compounds as well as the techniques used for known migrant determination from FCMs into food. Identification of Possible Migrants To identify the potential migrants in FCMs, it is important to know the type of material being analyzed. For that purpose, infrared spectroscopic techniques, with the support of libraries, are very useful analytical tools to obtain reliable identification of the type of polymeric FCMs. The most likely migrants are based on the synthetic scheme for a given FCM. For example, polyethylene terephthalate) would be expected to contain terephthalic acid, and epoxy resins would likely have bisphenol A. To verify the presence of the compounds, an extraction of the materials should be performed. The analytical techniques should be able to separate and detect most of the potential migrants, from very polar to non-polar compounds. The most employed analytical techniques are likely gas chromatography (GC) and liquid chromatography (LC) (6–10). It is important to ensure that experimental conditions capable of determining these compounds are used, and they should be selected before starting the analysis. In GC, the type of column coating is very important in order to ensure that the compounds of interest are retained. The GC oven should be programmed to start at a low oven temperature and increase temperature until the column maximum is reached. The highest temperature should be equal to or greater than the injection port temperature. The injecting port temperature is very important to ensure that the temperature is sufficiently high enough to volatilize the substances yet not hot enough to degrade the compounds of interest. A temperature program is recommended for the proper identification of compounds. In LC, the most common column used in the analysis of FCMs is the C18. It is frequently used because it can retain most analytes with the exception of very polar compounds, which can be retained using normal phase LC or a hydrophilic interaction liquid chromatography (HILIC) column. The rate of the solvent gradient of the mobile phase should be low enough to separate the compounds, and in the case of a C18, the chromatographic run should start with a mobile phase with a high percentage of aqueous solvent and end with 100% organic solvent. Temperature is another relevant parameter that must be also controlled. Numerous detectors can be used in conjunction with chromatographic separations. Mass spectrometry (MS) can give information about the molecular masses of the analytes as well as fragmentation data, which can be used for structure elucidation. In order to collect maximum data, it is important that the detectors are set to cover a wide mass range. Typically, polymeric compounds found in FCMs with molecular weights greater than 1000 Da are not considered to pose a health concern because they generally not absorbed by the intestinal track. In most cases, compounds with high molecular weights are nonvolatile and not amendable to GC analysis. Therefore, setting the mass range to a maximum 127 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
of m/z 550 would be more than sufficient to detect most of volatile compounds in GC–MS analyses. Choosing the ionization source is also extremely important for analyte identification. In LC–MS analyses, electrospray ionization is a soft ionization technique and is appropriate for compound identification since it produces high intensity molecular ion peaks and little to no fragmentation products. The polarity of ionization (+ or -) is also an important parameter to consider as some analytes will only fragment in one setting. The high-resolution mass spectrometry (HRMS) is very useful because it provides accurate masses of the eluting compounds. Databases populated with the accurate masses of potential migrants should be used to match the accurate mass of unknowns in the extract. Other types of detectors, such as diode-array detector (DAD), fluorescence detector (FLD), charged aerosol detection (CAD), flame ionization detector (FID), and evaporative light scattering detector (ELSD), can be utilized to provide complementary data. Spectrophotometric techniques collecting data over a wide spectral range provide data that can be interpreted to identify unknowns. Universal detectors such as FID, CAD, and ELSD can be used to analyze substances not detected by other instruments. When there are no analytical standards available, the identification of unknowns is complicated. It is important to use known standards to validate the chromatographic methods and calibrate the elution axis in both GC and LC. A way to gain confidence that the analytical methods will detect your compounds of interest is to use analytical standards in the same class of compounds as the suspected migrants and/or have a wide range of volatility and chemical properties. In Figure 1, an example of GC–MS chromatograms used in the analysis of an adhesive extract can be seen. On the top chromatogram, it can be observed that all the peaks corresponding to Grob’s mix were successfully detected. The middle chromatogram is a mix of standards commonly used in manufacturing adhesives, which were analyzed using the same analytical conditions. In the bottom figure, a chromatogram from the analysis of the extract of an adhesive shows the presence of several peaks that do not correspond to the peaks in the standards. One advantage of GC–MS is that there are large spectral libraries that can be used to identify unknowns in the extract with high confidence. In the presented case, several compounds were tentatively identified in the extract. However, to confirm the identity, analysis of analytical standards was required to demonstrate retention time and spectral matches. For the case example of Figure 1, several analytical standards were purchased in an effort to confirm peak identity, but only one matched with the retention time and mass spectrum; therefore, only one compound was successfully identified in the adhesive extract. The identified compound is listed in 21 CFR Parts 170–199 (1). It is important to note that even when all these conditions are optimized, there is no guarantee that 100% of compounds will be detected and/or identified.
128 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
Figure 1. GC–MS chromatograms of Grob’s mix (top). Standards of adhesives (middle). Adhesive extract (bottom).
When no analytical standards are available, researchers should either synthesize the tentatively identified compounds or isolate the compound from the sample and purify it. To synthetize a new compound, a synthesis pathway should be designed and separation techniques such as liquid–liquid or solid–liquid extraction can be used for compound purification. Gel permeation chromatography is often employed to isolate a compound from an extract. Once the standard(s) is(are) obtained, techniques such as 13C and 1H nuclear magnetic resonance spectroscopy and two-dimensional nuclear magnetic resonance techniques (COSY, TOCSY) can be used for compound characterization. A good example of characterization of a substance related with FCMs is the study performed by Paseiro-Cerrato et al. (11). Based on a previous study (12), the authors observed that the amines employed in the experiment were not stable in fatty foods. They hypothesized that amines could react with components of fatty foods such as triglycerides and/or fatty acids and that, because of this reaction, fatty acid amines (FAAs) could be formed. The synthesis of two FAAs was performed, and a full characterization was conducted obtaining satisfactory results. To prove that FAAs could be formed in real food, a sample of olive oil was spiked with an amine (m-xylylenediamine). Afterwards, extraction of the potential FAAs was conducted obtaining good results when comparing the standard with the spiked food, suggesting that this reaction could occur in real foodstuff.
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Analysis of Target Migrants Once the researcher has analytical standards, method development can be performed. The first step is optimizing extraction from a given matrix or set of matrices. The use of separation techniques (i.e., solid phase extraction) can be used to obtain good results. Because concentrations are sometimes low, extraction techniques should provide both sample clean-up as well as analyte concentration. After separation of the target compounds from the matrix, conventional analytical techniques can be used (LC–DAD, LC–FLD, GC–MS, and GC–FID) to obtain quantitative results. Parameters such as limit of detection, limit of quantitation, recovery, stability, and linearity should be performed with the use of the standards to validate the analytical methods. The use of isotopically labeled internal standards and the standard addition method should also be considered. Once the method has been validated, the concentrations of the migrants in the FCMs, food, and/or food simulants can be determined. In the EU, if the measured concentrations comply with the specific migration limits and with 1935/2004, the sample complies with legislation. In the United States, the levels in food or food simulants are used to estimate consumers’ exposure and perform a safety assessment. The results can also be used to better understand behavior of chemicals in the different food matrices and to study the kinetics of migration. Examples of validated analytical methods using isotopically labeled internal standards and discussion of results are the studies performed by Noonan et al. (13) and Paseiro-Cerrato et al. (14), where analysis of monomers from can coatings were conducted in food and food simulants, respectively.
Analysis of Brominated Flame Retardants: A Case Example Brominated flame retardants (BFRs) are chemicals that can be present in FCMs as contaminants if good manufacturing practices are not properly followed during the recycling process. Recently, studies on the determination of BFRs in FCMs were published (15, 16). To analyze BFRs in FCMs, a GC–MS method was developed (17). The samples were extracted with toluene at 40 °C for 24 h. A GC (Agilent 7890B) coupled to an MS (Agilent 5975C, both Agilent Technologies, Santa Clara, CA) was used. For the extract analysis, an appropriate GC column (Rtx-1614 15 m x 0.25 mm ID, 0.10 μm, Restek, Bellefonte, PA) and settings were selected: carrier gas flow was 1 mL/min, inlet temperature was set at 250 °C, oven temperature program started at 125 °C for 2 min and then increased at 15 °C per min until 315 °C, then held for 5 min using a splitless injection. The method was validated using analytical standards including determination of correlation coefficient, limit of detection, limit of quantitation, and relative standard deviations. The method conditions allowed detection of a large variety of BFRs in FCMs. The study was extended to utilize direct analysis in real time (DART) coupled to an HRMS to identify BFRs in several FCMs without sample preparation. To perform the analyses by this technique, small pieces of the samples were cut and analyzed by DART-HRMS. Several consumer FCMs were purchased at online and retail stores in the United States for analysis for 130 Granvogl and MacMahon; Food-Borne Toxicants: Formation, Analysis, and Toxicology ACS Symposium Series; American Chemical Society: Washington, DC, 2019.
BFRs. In one of these analyzed samples, the characteristic bromine spectra were detected. The spectra were compared with a BFRs standard solution (Figure 2). Results obtained in both analytical techniques were in good agreement. The study’s data obtained from DART-HRMS and GC–MS suggested that only one sample of the 12 analyzed samples was contaminated. The GC–MS analysis confirmed the presence of a BFR contaminant in the sample. This is a good example of a method development that can be used to analyze compounds in FCMs.
Figure 2. Comparison of a DART-HRMS chronogram (top left figure corresponds to the standards, top right figure corresponds to the sample) and spectra of a potential contaminated sample (bottom right) and BFRs standards (bottom left).
Briefly, in this chapter, we have discussed FCMs, the regulations with which they must comply, and the challenges of testing migration. Several analytical strategies for the analysis of migrants were discussed. The determination of the concentration of migrants in food must be evaluated to help protect consumer health.
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13. Noonan, G. O.; Ackerman, L. K.; Begley, T. H. Concentration of bisphenol A in highly consumed canned foods on the U.S. market. J. Agric. Food Chem. 2011, 59, 7178–7185. 14. Paseiro-Cerrato, R.; Noonan, G. O.; Begley, T. H. Evaluation of long-term migration testing from can coatings into food simulants: polyester coatings. J. Agric. Food Chem. 2016, 64, 2377–2385. 15. Puype, F.; Samsonek, J.; Knoop, J.; Egelkraut-Holtus, M.; Ortlieb, M. Evidence of waste electrical and electronic equipment (WEEE) relevant substances in polymeric food-contact articles sold on the European market. Food Addit. Contam., Part A 2015, 32, 410–426. 16. Puype, F.; Samsonek, J.; Vilimkova, V.; Kopeckova, S.; Ratiborska, A.; Knoop, J.; Egelkraut-Holtus, M.; Ortlieb, M.; Oppermann, U. Towards a generic procedure for the detection of relevant contaminants from waste electric and electronic equipment (WEEE) in plastic food-contact materials: a review and selection of key parameters. Food Addit. Contam., Part A 2017, 34, 1767–1783. 17. Paseiro-Cerrato, R.; Ackerman, L.; DeJager, L.; Begley, T. H. Analysis of flame retardants: a survey of food contact materials (poster). 254th ACS National Meeting, Washington, DC, August 20–24, 2017.
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