Exploring the sensitivity of the zone of inhibition test for leachable biocides from paper and board food contact materials, and improvements thereof.

The zone of inhibition method to test the release of biocides from paper and board food contact materials was evaluated. The method tests the paper by placing a small specimen directly onto culture plates of Bacillus subtilis and Aspergillus niger. The principle is that any extractable biocide will diffuse from the paper into the surrounding nutrient medium and so inhibit growth of the microorganism in the vicinity. The test was found to have insufficient sensitivity for assuring food safety, where detection limits for migration at or below the mg l(-1) (parts per million) level are needed. Also, the test does not mimic the actual or foreseeable conditions of use since most paper/board materials are not intended for direct contact with an aqueous medium for up to 3 days at 30°C (B. subtilis) or 25°C (A. niger), which are the incubation conditions used. The sensitivity of the test was increased approximately 100-fold by preparing a concentrated extract of the paper to be tested and applying this extract to the assay via a blank paper carrier. This was done using methanol as a good solvent for most biocides, as a proof of principle. Other solvents or food simulants could be used to mimic the conditions of use intended for the particular paper/board samples under examination, e.g. contact with dry, fatty, aqueous or acidic foods, hot or cold. Twenty-four plain (unconverted) paper and board samples and 100 food packaging samples were evaluated using the modified procedure. The results revealed that the method has been developed to the stage where background cytotoxic action of normal paper constituents gives a weak response. Unlike the original method, therefore, the modified method with its improved sensitivity and the facility to link with the intended food contact conditions may be considered a suitable bioassay screening test to complement chemical analysis of paper/board for composition and migration.

Use of overall migration methodology to test for food-contact substances with specific migration limits.

This work investigated if overall migration test procedures could also be used to test for the migration of specific substances from plastics. The overall migration test procedure used was the evaporative gravimetric method used with volatile food simulants. Thirty food-contact substances (additives and monomers) were tested for their chemical stability and volatile loss during the heated evaporation stage of the overall migration procedure. Eighteen of the 30 were determined in an acceptable yield. It is concluded that in the list of approximately 620 European Union substances that have specific migration limits of 5 mg kg(-1) or higher, and based on considerations of stability and volatility, more than half could be amenable to control using overall migration methodology. This is particularly the case for inert plastics with low intrinsic overall migration values of oligomers. This means that based on the overall migration test result found, testing laboratories could decide on a case-by-case basis if known additives and starting substances are covered by the overall migration result and no separate testing would be required for specific migration, with time and resource cost savings.

Migration of contaminants by gas phase transfer from carton board and corrugated board box secondary packaging into foods.

The gas phase transfer of substances from carton board (CB) and corrugated box board (CBB) through intervening layers to foods was studied. Substances covering a boiling point range of 252-425 degrees C and a range of polarities were incorporated into CB and CBB secondary packaging. Benzophenone was present in some CB materials. Where it was not already present in CB or CBB secondary packaging, it was deliberately incorporated for transfer studies. Transfer of substances was measured in nine foodstuff types stored in the secondary packaging at ambient and sub-ambient temperature. The foods were packaged in primary packaging materials that would be used in retail. Two food types were packed and stored in both single- and multipack formats. Foods were sampled at 0, 10, 30, 90 and 200 days and analysed by gas chromatography-mass spectrometry after high-performance size exclusion chromatography clean-up. Percentage transfer was between 0 and 100%. The overall trends were increased transfer of substances with increased storage time; a more rapid transfer of the more volatile substances compared with the less volatile ones and higher levels of transfer of the more volatile substances. No transfer of diheptyl phthalate (DHP) (bp 425 degrees C) as an incorporated substance was detected to any foods over the test period. The presence of an additional layer of packaging (multipack versus single pack) was shown to reduce transfer up to fourfold over 200 days and to increase the lag period for transfer. In terms of slowing transfer, metallized PP/PP laminate proved a more effective barrier than PP which was more effective than paper. It is postulated that there is a cut-off threshold for transfer at ambient and sub-ambient temperatures. Substances that are less volatile than the cut-off are anticipated not to transfer from secondary packaging to foods stored for up to 200 days, where the substances are present in the packaging at or below the levels tested in this study (up to 1 mg dm-2). In this study the volatility cut-off threshold lay between that of 2,2-dimethoxyphenylacetophenone (2,2-DMPAP) (an incorporated substance with bp 352 degrees C) and DHP. Ideally, the cut-off threshold should be expressed in terms of vapour pressure in the packaging material. In practical terms, it may be more appropriate to express as partition coefficient as this is simpler to determine experimentally.

Test method for measuring non-visible set-off from inks and lacquers on the food-contact surface of printed packaging materials.

The main objective was to develop a technique to expose spots of invisible set-off of inks and lacquers on the food-contact surface of food-packaging materials. Set-off is the unintentional transfer of components of printing inks from the outer printed surface onto the food-contact surfaces. The target sensitivity was 20 microg cm(-2) and the technique should be capable of examining large areas of printed substrate for no more than 4% coverage by set-off. These requirements equate to an ability to detect a worst-case migration potential of less than 50 microg kg(-1). Other objectives were the industrial requirements that the equipment should be inexpensive, should be easy to use by existing personnel and should preferably be non-destructive with a clear criterion for pass or fail. The approaches investigated included chemical analysis of solvent extracts, Fourier-transform infrared spectroscopy and microbeam analytical techniques, but these were found to be cumbersome and had only limited success. The objectives were achieved using an optical approach to excite and observe luminescence from invisible set-off. In model experiments, resins were applied to different substrates (plastic, paper and cartonboard). For a given resin on a given material, the key to success was to maximize the discrimination between the luminescence from the resin and that from the substrate by selecting the optimal combination of exciting wavelength and viewing goggles with selective wavelength filters. The required level of detection (20 microg cm(-2)) was achieved or exceeded for all ten resins tested on three different plastics. It was also achieved for two different papers and in all but four cases of the resins on three different cartonboards. Quantitation was achieved by the use of a calibration palette prepared using different quantities of resin spotted onto the relevant blank packaging material.

Investigations into the potential degradation of polycarbonate baby bottles during sterilization with consequent release of bisphenol A.

Twenty-four brands of plastic baby feeding bottles were purchased and all were found to be made of polycarbonate. Taking a batch of one representative sample, the polymer was tested for stability and possible release of bisphenol A following domestic practice of sterilization. Sterilization was by alkaline hypochlorite, steam, or washing in an automatic dishwasher at 65 degrees C with detergent. A total of 20 cycles of sterilization and subsequent food use were performed for each of the three procedures. Bisphenol A migration was in all cases not detectable in infant feed using a very sensitive method of liquid chromatography with fluorescence detection with a 0.03 mg/kg detection limit.