Influence of polystryrene and polyethylene packaging materials on food quality

Polystyrene (PS) and polyethylene (PE) used for packaging of food were studied on their effect on product quality. Different types of PS were tested: General purpose polystyrene (GPPS), high impact polystyrene (HIPS, which contains a dispersed rubber phase) and several blends of these types. PS contains detectable amounts of residual monomer, which has an unpleasant odour and/or taste. When the concentration in the polymer is too high, it could give a taint to the packed product after migration. Several aspects of migration of styrene monomer were evaluated. Migration of styrene increases with increasing fat content in a product, but the styrene migrated was only a small part (3% after incubation during 14 days at 40°C)of the total amount of residual styrene present in the polymer.The sampling method used influences the level of migrated styrene in corn oil. Immersion sampling of cut pieces of high impact grade PS types showed a much higher level of migrated styrene than utilisation of sampling cells. Cut edges of the samples cause a high initial leakage of styrene from cut rubber particles. Also vapour phase migration exists and is of considerable interest for solid foods. In that case integral contact between the surface of the packed product and PS is not possible. For GPPS only little differences were found between the sampling methods. The composition of PS influences the level of migrated styrene. Migration increases linearly with increasing amount of HIPS in blends with GPPS. Migration is faster at higher temperatures and is linearly dependent on the content of residual styrene monomer in the polymer.Some food products were also studied on a taint caused by styrene migration. Cocoa powders for drinks and chocolate flakes were exposed to pieces of PS and sensorily evaluated using short-cut signal detection measures on differences between control and test samples and on recognition of styrene. Compared to control samples significant differences were detected in milk -and plain chocolate flakes, but not in the cocoa powders for drinks. Styrene was clearly recognized in the flakes at contents of approximately 1.2 ppm.Recognition threshold values of styrene were sensorily determined in oil in water emulsions with different fat contents (3 - 30%). The recognition threshold concentrations of styrene increase linearly with increasing fat content in the emulsions and ranged between 0.3 - 2.1 ppm. Recognition thresholds of styrene in yoghurts (0.1 - 3% fat) were found in the range 36 - 171 ppb. At their threshold levels the concentrations of styrene in the aqueous phases and the vapour phases of the emulsions were similar at 15 and 0.41 ppb, respectively. In commercial yoghurts packed in PS the actual styrene contents ranged between 2 - 11 ppb at their expiring date. These results indicate that PS is an acceptable packaging material for yoghurts.PE is widely used in the food packaging industry as mono -or multilayer system as well as laminated with carton and aluminium. A sensory descriptive analysis was carried out for a taint in water packed in test pouches made of PE lined aluminium. The taint could be described by 6 attributes: synthetic, astringent, musty, sickly, metallic and dry. Dynamic headspace analysis of water in contact with the PE layer of the test pouches showed(C 4 - C 11 )carbonyl compounds, which could be responsible for the taint described. Commercial mineral water packed in PE laminated aluminium/ cardboard was evaluated by combined gas chromatography and sniffing port analysis after incubation at different temperatures. similar descriptors as mentioned were found for individual components, which were migrated into mineral water. These components were identified as mainly aromatic hydrocarbons, while also carbonyls were detected. The concentrations of these migrants in the mineral water were in the low ppb range (10-15 ppb).Finally, some aspects of absorption of aroma compounds from artificially flavoured commercial drink yoghurts into PE bottles were studied. Short chain compounds appeared to remain preferably in the yoghurts, while compounds of medium chain length were present in both the drink yoghurts and the packaging material. Compounds with more than 8 carbon atoms and highly branched components tend to be absorbed by the PE packaging material and could, therefore, contribute less to the flavour of the product. The influence of juice composition on the absorption of flavour components was illustrated for limonene absorption from an imitation juice and from juices with and without addition of pulp. The presence of pulp particles diminishes the extent of absorption of limonene by the packaging materials.