Document Type : Research Article
Authors
Shahid Beheshti University
Abstract
In Iran, the majority of vegetable oil producers , use PET for packaging their products . Due to high solubility of PET oligomers in the oils , and shelf life of liquid oils , it is expected that some compounds migrate into the oil .
This study was carried out to determine the amount of migration of terephtalates from PET bottles into sunflower oil and the effect of temperature and storage time on the degree of migration. 42 samples of liquid sunflower oil packed in one litre PET bottles, from single production bach of pars vegetable oil, were kept at 20˚C and 40˚C. Experiments were carried out on three bottles taken at different periods of time (10, 20, 30, 70, 145 & 202days). According to Castle method , alkaline hydrolysis of all PET oligomers to terephthalic acid followed by its methylation to dimethylterephthalate (DMT) for the measurement of DMT, derivative UV spectrophotometer was used according to Reeves.The results showed that the maximum level of migration of terephthalates at 20 ˚C was 29.43 + 0.93 and at 40˚C was 29.58 + 1.15. Therefore the amount of overall migration obtained in this research is lower than the international permitted level (lower than 60 ppm) and sunflower oil after the final migration can be safely consumed. Migration increased with the passage of time until it reached to its highest level and then stopped (P=0). Migration is faster when the temperature is increased (P=0.014). Therefore, migration is dependant on both temperature and contact time (P=0.001). In this research, linear dependence between migration and square root of time has also been demonstrated (r = 0.96 at 20 ˚C from time zero to 145 days and r = 0.95 at 40˚C from time zero to 70 days). Reproducibility of the method was evaluated by calculating the relative standard deviation which was equal to 3.21% and the detection limit of the method was 0.21 ppm. In conclusion migration of PET oligomers was dependant on time and temperature, until it reaches an equilibrium.
Keywords: Plastic bottle, Migration, Sunflower oil, Polyethylene terephthalate (PET), Derivative UV Spectrophotometry , PET oligomers.
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