Evaluation of a predictive mathematical model of di-(2-ethylhexyl) adipate plasticizer migration from PVC film into foods.

The diffusion coefficient of the plasticizer di-(2-ethylhexyl)adipate (DEHA) in Cheddar cheese (Df) was determined by measuring the extent to which DEHA penetrated cheese that was placed in intimate contact with artificially DEHA-contaminated cheese. Slices (20 microns) of cheese from the boundary layer, into which DEHA had migrated, were microtomed at -40 degrees C, and analyzed for DEHA by gas chromatography (GC). Mean values of Df determined by graph fitting experimental and calculated data were 1.5 x 10(-9) cm2 s-1 at 5 degrees C and 3.0 x 10(-8) cm2 s-1 at 25 degrees C. The partition coefficient (K) of DEHA between cheese and PVC film was derived from the partition coefficients of DEHA between acetonitrile (ACN) and cheese lipid, ACN and cheese solid, and ACN and PVC film. The mean values of K between cheese and PVC film were estimated to be 0.70 at 5 degrees C and 0.58 at 25 degrees C. The estimated values of Df and K were then used in a mathematical model (Till et al. 1982) to predict migration levels of DEHA into cheese. Good agreement with previously published experimental data was obtained. Extrapolation of the prediction of DEHA migration into fatty foods, such as salami and avocado, was also successful (ratio of experimental to predicted results within a factor of two). The values of Df and K for cheese are, however, inappropriate for modelling non-fatty foods such as meat, cakes, fruit and vegetables. Predicted values for these foods were typically 3-10-fold too high. More accurate predictions would probably be obtained if values of Df more relevant to these foods are used. The predictions were relatively insensitive to the value of K.

Permeation of water through the polymeric components of boil-in-bag laminates.

Diffusion coefficients and equilibrium uptake have been measured for water and 3% acetic acid in film of PETP, lldpe, nylon 6 and nylon 66, and also in some isocyanate adhesives. These materials are used in the construction of boil-in-bags for food. The three methods of measurement used were permeation from a bag, mass uptake, and the use of a novel technique using isotopically labelled water. The principal temperature of investigation has been 100 degrees C. Differences in the permeation parameters for water and 3% acetic acid were small for PETP, but surprisingly large for an inert material such as lldpe. With the nylons differences could readily be ascribed to the fact that these materials are bases. When immersed in boiling water there was no change in the degree of crystallinity of PETP, but lldpe and nylon 66 showed small increases.