Gas Barrier Protection And Shelf Life

For foods that are sensitive to oxygen or moisture, gas barrier protection is the major function of the package in providing adequate shelf life, the time period during which the food maintains acceptable quality. For example, moisture can move from the external environment through the package into the headspace. This increase in relative humidity in the headspace can cause a moisture-sensitive food, such as potato chips, to have less crispness and a shorter shelf life. To ensure adequate shelf life, the package must help to reduce the moisture movement from the external environment to the headspace.

External environment

Package -

Internal environment (headspace)

Food

Figure 1. Physical components of packaging system.

Movement of gases between the external environment and the headspace through the package can occur by means of permeation and leakage. Gas permeation is an important consideration in packaging foods with plastics, because food packaging plastics are permeable to moisture, oxygen, carbon dioxide, nitrogen, and other gases. The gas-permeation rates of most interest are the oxygen transmission rate (OTR) and water vapor transmission (WVTR). Gas permeation is not an important consideration in packaging foods with metal or glass because these materials are not permeable.

Leakage can occur in packages made of plastics, metal, glass, or paper. Pinholes are sometimes found in thin metal foils and metallized films. Channel leaks are most commonly found in weak seals or contaminated seals. Pinholes and channel leaks can shorten the shelf life of a packaged food and, in some cases, allow microbial penetration, leading to a potential health risk.

Shelf life is best determined by actual field studies, although accelerated laboratory studies and computer simulations can sometimes provide useful shelf life predictions (1,3). The variables that affect the shelf life of packaged food are discussed next.

Shelf Life of Oxygen-Sensitive Foods

Equation 3 predicts the shelf life of packaged food that is oxygen sensitive. The equation assumes the package is made of a plastic material with uniform thickness and has complete integrity (no pinholes and channel leaks); hence, permeation is the only means of oxygen transfer. The equation can assist in understanding the relationship between the shelf life and the physical components of the food packaging system—the food, package, headspace, and external environment. Two useful terms, permeability CP) and maximum allowable oxygen (02max), are introduced.

The OTR of a permeable package (eg, a plastic pouch) from the external environment to the headspace can be calculated using ts =

Q2max^/

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