The Effect of High-Pressure Processing on Tray Packages with Modified Atmosphere

High-pressure processing (HPP) is a small, but growing and profitable technique to extend the shelf life of high-quality food products. As tray packages with modified atmosphere packaging (MAP) provide better product presentation and also improved product protection, it seems logical to combine HPP with MAP. Due to the fact that the used gases such as oxygen, nitrogen and carbon dioxide are in a supercritical state during HPP, it is important to give extra attention to these conditions. Several studies were performed dealing with the influence of high pressure on the mechanical and/or barrier properties of packages and polymers. However, little information is known about the combined effect of MAP gases and high pressure on packaging. This study hence evaluates the influence of headspace gases on the morphology and integrity of packages subjected to HPP. Pressure-related changes of the morphology of polymers as commonly used for packaging will be shown. Density as well as crystalline and amorphous content was analyzed quantitatively with Raman spectroscopy by varying headspace volume (15-50 % of the total package), headspace gas composition (air, CO2, N-2 and a mixture of 20 % CO2/80 % N-2), multilayer structures, film thickness and flexibility of the lid. Additionally the influence of headspace gases in HPP on the barrier properties of an organic and an inorganic material and on the migration of additives into liquid food simulants has been studied.