Sorption of aroma compounds in PET and PVC during the storage of a strawberry syrup.

The sorption of 14 aroma compounds into PET and PVC was monitored during storage of a strawberry syrup for 1 year. Concentrations in the syrup and in the polymer were determined during storage and compared with previously published results obtained with glass bottles. Apparent partition coefficients between the polymer and the syrup (noted K app) were estimated from experimental kinetics without reaching equilibrium K app values and optimally identified from the kinetic data obtained between 30 and 90 days. They exhibited a similar behaviour for both polymers with values were between 2 x 10(-5) and 2 x 10(-3), 4 x 10(-5) and 3 x 10(-2), respectively, for PET and PVC. The variation of K app values in PET was mainly correlated to the polarity of tested compounds as assessed by their log P values. By contrast, the variations in K app values for PVC were mainly related to their chain lengths. Due to slightly higher partition coefficients and diffusion coefficients in PVC compared with PET, the amount of absorbed aroma was four times higher in PVC than in PET; however, the amount of absorbed aroma compounds was less than 0.1% of the initial amount present into the syrup, except for octyl butanoate. The variation in concentration in the syrup was interpreted as a combination of a degradation process and a transport process into the packaging material. Both effects were particularly noticeable for both PET and unstable aroma compounds.