Testing Food Product Contact Packaging

September 2005

Testing Food Product Contact Packaging

By Richard Crowley
Contributing Editor

Ever since ancient times, when our ancestors used dried gourds, leaves and crude baskets to gather and store sustenance, packaging has played a crucial role in the freshness, safety and convenience of food products. The evolution of packaging techniques has been key to an unprecedented level of high-quality, safe and healthy food.

As the use of innovative packaging methods increases, it creates a corresponding effect on the regulatory and experimental guidelines for determining the impact of packaging components on safety. The primary concern is the migration of indirect additives from packaging that can cause health concerns and adversely affect the taste, color and aroma of foods. In the case of functional foods, migration could potentially have a negative effect on the efficacy of the active ingredient.

Regulatory review
Both the United States and the European Union have stringent regulations pertaining to the approval of food-contact materials. Regulatory mandates define substances that come into contact with food, dietary supplements, packaging and machinery as potential indirect food additives, and any component of packaging that could migrate into the food must be approved based on premarket safety-testing results following the guidelines of the Food Contact Substance Notification System (see the 2002 Federal Register, Vol. 67, No. 98, for complete details).

The best-case scenario is that no migration from the food contact material into the food occurs under the intended conditions of use. A second possibility is that although a substance might be shown to migrate, it is found in GRAS quantities. In the final scenario, substances found to migrate that are not considered GRAS must undergo extensive studies to prove their safety. Regardless of the scenario, manufacturers must submit migration data. However, the amount of testing required and the analytical challenges encountered vary depending upon the materials used and their regulatory status.

Measuring migration
Migration data are the quantitative description of the substances that transfer from the contact material into the food and are required for regulatory compliance. Testing requires the design of protocols for identifying potential classes of migrating substances under the conditions which the product and packaging will be used. In addition, tests should identify the data-quality requirements and define the method for determining the relationship between the migration and human dietary exposure.

Determining migration has proven difficult because the food products themselves, due to their heterogeneous nature, can interfere with the accuracy of the data. As a result, testing is done using solvents such as ethanol-water solutions and food oils that simulate the leaching action of aqueous, acidic, alcoholic and fatty foods. Choosing the right simulant for migration testing is a critical factor in accurate testing. If a material is regulated in the United States, the required simulants are specified in the regulations. If the material is not regulated, FDA defines the preferred simulants and guidelines for testing. Agencies in the European Union have published similar guidelines.

Extraction experiments yield samples of food-simulating solvent (matrix) that contain some quantity of the migrating substance (analyte). Determining the levels of these analytes in food-simulating matrices is often quite challenging. Because the fat content and pH are important factors in migration, analysts must choose the correct simulant for each test. The high temperatures to which multipurpose packages are exposed produce favorable conditions for migration, and the time and temperature parameters for analysis are determined by the conditions of use.

Extraction essentials
The extraction process isolates potential migrants through immersion of the packaging material in an extraction "cell" filled with the appropriate simulating solvent. Time and temperature parameters, the type of food-contact material, potential migrants and the simulants required determine the type of cell used. Extraction experiments may be broadly classified as single-sided, double-sided or exhaustive. The type of study conducted depends upon the construction of the test material and its thickness, as well as the volume of food-simulating solvent used and the surface area of food-contact material to be extracted. Single-sided extractions are most often used for coated materials, multiple and barrier layers, or structures less than 0.02 in. thick.

Single-sided extractions are done using two pieces of the packaging material that are separated by an inert spacer, thus defining a volume. This layered construction is secured such that the volume can be filled with food-simulating solvent. Double-sided extractions involve immersing the test material in a cell or autoclave containing the food-simulating solvent. The vessel in which the simulating solvent and the material to be extracted must be capable of withstanding the pressures generated by heating the solvents past their boiling points. The most common application for exhaustive extractions is in residual studies and the quantification of oligomers that migrate from polymeric materials.

Quantification quandaries
After extraction, the additives are isolated and measured using gravimetric, chromatographic and spectroscopic techniques. The methods are designed for sensitivity and have the capability to detect indirect additives in the low parts per billion (ppb) range. Selection of the appropriate technique is specific to the analyte and matrix. Scientists increasingly use mass spectroscopy to quantitate a number of representative compounds from polymeric formulations. Gas chromatography is appropriate for volatile analytes and many organic soluble analytes. Separation is based upon polarity of the analyte molecule and changes in its volatility with increasing temperature. Liquid chromatography (LC) is appropriate for nonvolatile analytes and many water-soluble analytes. Separation is based on polarity of the analyte molecule and changes in its solubility in different solvents.

In some cases, the method detection limits dictated by FDA are generally lower than typical instrument detection limits -- particularly in the cases where migrants are carcinogens. As a result, methods for concentrating the analyte or otherwise enhancing sensitivity are the rule rather than the exception.

Quantification of migrating oligomers is the most-challenging analytical task faced in a migration study. A type of LC known as gel-permeation chromatography (GPC) is usually employed in conjunction with evaporative-light-scattering detection (ELSD). In GPC, separation is based on size of the oligomer molecule. In ELSD, the eluent from a GPC column is forced through a heated orifice and aerosolized. The solvent evaporates, leaving the solute molecules that are quantified as they pass through a laser beam.

Exposure evaluation
The ultimate goal of the study of indirect additives is to determine potential harmful effects to the consumer. To evaluate these risks, the food-contact notification process mandates the submission of cumulative estimated dietary intake (CEDI) values. These values are based upon the estimated dietary intake (EDI) which in many cases are established by FDA.

To assess human exposure, migration data are expressed as the mass of migrant per unit of surface area of test material extracted. This value is then used to calculate the potential dietary exposure. The raw migration data are expressed as mass of migrant per unit volume of food-simulating solvent. The mass of migrant per unit surface area of test material extracted is determined for each applicable food-simulating solvent. The human dietary exposure is then calculated using the estimated daily intake and consumption factor -- i.e., fraction of the diet expected to be in contact with the packaging material -- and the concentration of the analyte in the food-contacting material. The concentration is the mass of migrant per unit surface area of test material extracted into each applicable food-simulating solvent.

If the maximum potential dietary concentration of a substance is below 0.5 ppb and the substance is not a known carcinogen, FDA considers it safe based on statistical analysis of the available data. The material can then be used without having to file a formal indirect-food-additive petition. The dietary concentration is calculated by multiplying the fraction of the food in the diet that is in contact with the packaging material (i.e., the consumption factor) by the average concentration of the additive in food. If the dietary concentration is above 0.5 ppb, a more-comprehensive regulatory process is required.

Safety standards
When evaluating the safety of recycled materials, the main concerns are chemical contamination, structural integrity and microbial contamination. Although FDA requires that recycled materials meet the purity standards for virgin material, safety factors for using recycled materials in packaging are more complex. As a result, additional characterization and testing beyond that used for virgin materials are required.

FDA has identified a set of relatively nontoxic surrogates (i.e., model compounds) for the estimated 60,000 substances that could potentially be found in recycled plastics. In addition to these surrogates, successful studies have been acceptable to FDA using other compounds. In most cases, the alternates are less toxic, thereby increasing safety. Some of the surrogates have the ability to simulate more that one type of compound.

The probable level of consumer exposure and the inherent toxicity of a substance determine the requirements for toxicology testing of substances that come in contact with food. FDA bases its toxicology standards on determining the levels in the diet and has indicated that genotoxicity testing is needed for substances with an exposure level above 0.5 ppb. The recommended testing includes gene mutation in bacteria (i.e., Ames test) and either an in vitro test with cytogenetic evaluation of chromosomal damage using mammalian cells or an in vitro mouse lymphoma TK assay. In addition, an in vivo test with cytogenetic evaluation of chromosomal damage and subchronic oral toxicity test are recommended. In some cases, if the Ames test results are clearly negative, the in vivo tests might not be required.

Traditionally, the role of packaging was to prevent contamination and preserve freshness. Now, many more factors impact the design of these essential product components. As new methodologies such as active, smart and antimicrobial packaging are developed, a comprehensive evaluation of the potential for translocation into consumer products is needed.

These considerations will become more essential as regulatory initiatives approach international harmonization, new substances are developed and analytical methodologies improve. With the knowledge gained from these studies, the food and packaging industries can be more efficient in developing new methods and materials without increasing the potential for migration of harmful indirect additives.

Richard Crowley is the editor of the Covance Food Science newsletter and the author of numerous articles on food analysis. He has a B.S. in Agricultural Journalism from the University of Wisconsin, Madison and is a member of the National Association of Science Writers.

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