Interaction between the package and the packaged product: Effects on respiratory and aroma volatiles

We are able to describe oxygen levels in packages composed of polymeric films using relatively simple mathematical equations. The equations incorporate film permeability, the respiratory response to oxygen and the temperature-dependence of both processes. Aroma volatiles tend to have sorptivities that cover a wide range, often orders of magnitude higher, and the diffusion coefficients tend to be much lower than for oxygen and carbon dioxide. In addition, interaction of the volatile with the film is such that permeability does not always increase with temperature in an Arrhenius-type fashion. However, if rate of permeation of aroma volatiles is mathematically describable, the accumulation of aroma volatiles can be modelled in conjunction with O-2 and CO2. An example using hexylacetate production from a sliced apple product is presented. Incorporated into the model is the effect of O-2 On the rate of fermentative metabolism, which may relate to off-flavour production. The modelling approach presented can be used to predict O-2 levels, hexylacetate levels and fermentative activity as a function of temperature and film thickness.