Permeability measurements to control the preservation of packaged foods

Outside short and local circuits, food is packaged in single-use packaging (or packaging systems), sometimes recyclable or (soon) reusable. Packaging must therefore be seen as an essential "partner" in the preservation and stabilization of foodstuffs.

In this article, plastic (polymer) packaging is treated as a dense membrane, or barrier, separating two environments: the external environment (ambient atmosphere) and the "confined" environment inside the packaging, known as the "headspace" (for vacuum packaging, this headspace is very limited, but it does exist). This may have a different gaseous composition from the ambient air, which is initially fixed during packaging (modified or protective atmosphere, for example). This composition evolves over time, as the membrane enveloping the food is the seat of material transport phenomena: gases and vapors (O ₂ , CO ₂ , N ₂ , water, flavors, etc.) enter or leave the packaging.

The nature of the packaging material(s), which depends on the part of the package under consideration (bottle and cap, tray and lid, etc.), the geometry (thickness and surface), the quantity of food and its properties, the environmental conditions (temperature and time, initial composition of the gaseous media in the initial headspace), the tightness of the closure system, etc., form a set of parameters that limit transfers to a tolerable incoming or outgoing quantity in terms of product shelf-life or quality. If the packaging/food pairing is inappropriate, these incoming and outgoing flows can lead to organoleptic deviations in packaged foods, reducing their shelf life.

These flows can be calculated and measured. Thinking about trade-offs (shelf-life/transfers) to optimize food packaging requires a detailed understanding of food properties and transport mechanisms.

This article deals with the transfer of the main gases (O ₂ , CO ₂ , N ₂ , water), recalling the theory of gas diffusion through dense membranes such as packaging. Quantities such as fluxes, permeance, permeability coefficient, are explained, as well as their measurement and conversion. The operation of the various permeameters on the market is presented. The difficulty of creating a sealed or purposely perforated system is detailed. Finally, the accelerated ageing of packaging/product combinations due to increased gas transfer is explained.