In an article published on January 5, 2016 in the peer-reviewed journal Food Additives & Contaminants: Part A, Roland Franz and colleagues from the Fraunhofer Institute for Process Engineering and Packaging, Freising, Germany discuss the appropriateness of a commonly used accelerated migration test (20% ethanol at 60°C for 10 days) for simulation of the long-term storage of beverages in poly(ethylene terephthalate) (PET) bottles. Based on migration kinetics and diffusion coefficients experimentally determined for select conditions, they suggest an alternative testing protocol.
Acetaldehyde (CAS 75-07-0) is a common PET contaminant generated during PET bottle manufacture. The specific migration limit (SML) of 6 mg/kg food set for this compound by the European Regulation No. 10/2011 is usually not exceeded. Complying with Article 3 of European Framework Regulation No. 1935/2004 is, however, more difficult, because acetaldehyde concentrations in the low µg/L can affect the organoleptic properties of the natural mineral water (giving a fruity or plastic-like off-flavor). For this reason, acetaldehyde scavengers, such as 2-aminobenzamide (CAS No. 88-68-6; anthranilamide), are often used during PET production in order to reduce acetaldehyde concentrations in the final product.
Migration tests mimicking realistic conditions for the use of PET bottles may require long storage times. Alternatively, long-term storage (over 30 days) at ambient temperature can be simulated by applying increased temperatures during shorter time periods, according to the Arrhenius equation. For example, the testing condition “10 days at 60°C” should cover long-term storage over 6 months at room temperature and below. Accordingly, the migration from PET bottles intended for storing natural mineral water, soft drinks and juices are often tested with 20% ethanol for 10 days at 60°C. Due to concerns that such conditions may lead to an overestimation of migration, the authors set out to determine the migration kinetics of 2-aminobenzamide into 20% ethanol and into carbonated natural mineral water at 23°C (room temperature) and 40°C. These data were then used to derive the diffusion coefficients and define the alternative “realistic contact conditions” for testing the migration of 2-aminobenzamide from PET bottles.
At 40°C, the diffusion coefficient of 2-aminobenzamide into 20% ethanol was significantly higher than for mineral water, indicating the occurrence of plastic swelling due to the alcoholic food simulant; at 23°C, swelling was not observed. Further, migration into mineral water was also assessed after 60 days at 40°C; according to the Arrhenius equation, this condition corresponds to 10 days at 60°C. This test resulted in 2-aminobenzamide concentrations close to or even higher than SML. In contrast, after “realistic storage conditions” of around one year at room temperature and in the dark, concentrations of 2-aminobenzamide complied with the SML in all cases.
The authors formulate conclusions that “have consequences for migration testing” for PET bottles. First, the determined diffusion coefficients can be used for modelling of 2-aminobenzamide migration into water. Second, since acetaldehyde scavenger is typically used only in PET bottles for mineral water, water itself should be used as food simulant for compliance testing. Third, a temperature of 60°C appears to be too high as it “may already lead to swelling effects even in contact with water and […] may cause physical changes like deformation of thin PET bottle wall structures”. The authors suggest that 40°C is “much closer to realistic storage temperature.” Since even at this temperature swelling was observed with 20% ethanol, the authors conclude that actual migration testing is more conservative than migration modelling.
The reaction product of acetaldehyde and its scavenger, 2-aminobenzamide, is the chemical 2-methyl-2,3-dihydroquinazolin-4(1H)-one (CAS 54764-01-1). It is not regulated specifically and no information is available on the toxicity of this substance and its migration into food.
Franz, R., et al. (2016). “Diffusion behaviour of acetaldehyde scavenger 2-aminobenzamide in polyethylene terephthalate for beverage bottles.” Food Additives & Contaminants: Part A 33:364-372.