Reuse and Recycling of Food Packaging - Odour Related Aspects of the Use and Misuse of PET Beverage Bottles

Abstract: The reuse and closed-loop recycling of food packaging was studied in order to assess consumer safety and the sensory quality (e.g. taste and smell) of packaged food. Polyethylene terephthalate (PET) beverage bottles that were refillable or that contained recycled material, either in direct contact or with a functional barrier protecting the food, were investigated with focus on odorous compounds from normal use or from misuse. Used refillable PET bottles were analysed for suspected misuse, i.e. when consumers store something other than the original beverage in a refillable bottle before returning it for reuse. Two different types of bottles were investigated to represent contaminated bottles which the in-line detection system both did and did not detect, i.e. sniffer-rejected and consumer complaint bottles. Previously, only a few of the compounds detected in post-consumer PET material had been suggested to originate from consumer misuse. In the studies presented here, a wide range of more than 50 possible misuse contaminants were identified in post-consumer refillable PET beverage bottles. A total of 29 different contamination categories were detected, including misuse by both food and non-food products. For refillable bottles, the inertness of the bottle material is an important property in order to avoid transfer of aroma compounds from one product to the next product filled in the bottle. A threshold odour number (TON) determination method was developed in order to characterise the inertness of refillable bottle materials. The method successfully differentiated between polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) materials. The materials were further analysed chemically using headspace gas chromatography coupled with mass spectrometry (GC-MS) to compare the aroma transfer potential. The results showed that the use of polyethylene naphthalate (PEN) instead of PET would lead to less off-odour problems in refillable beverage bottles. Multilayer PET bottles containing intentionally contaminated material simulating recycled PET were produced. Different combinations of contaminated and non-contaminated material in the three layers enabled investigation of contaminant migration both when the food was in direct contact with the recycled material and when it was protected by a functional barrier, i.e. a non-contaminated inner layer. Migration of four model contaminants from the produced bottles into three different food simulants, at two different storage temperatures was followed during 1 year. Additionally, bottles made from preforms stored at 40°C for 6 months prior to production of bottles were also studied. Storage conditions, type of model contaminant and type of food simulant were shown to greatly affect migration. The functional barrier succeeded in protecting the food from any detectable migration during 1 year of storage even under extreme conditions.