## Oxygen Transmission Rate (OTR)

All types of plastics are not gas-proof. Therefore oxygen will diffuse into plastic packages. As result the packaged goods can loose their properties. Food will for example change its taste and/or its color. The result is a short shelf life. For a long shelf life and a good quality of packages goods, it is important that packages have a good oxygen diffusion barrier.

The amount of diffusing in oxygen can be expressed by the oxygen transmission rate (OTR). The OTR describes what oxygen volume diffuses thorough a defined area during a defined time. The OTR is therefore an important benchmark for many packaging applications

*This can be achieved**with plasma coating.*The amount of diffusing in oxygen can be expressed by the oxygen transmission rate (OTR). The OTR describes what oxygen volume diffuses thorough a defined area during a defined time. The OTR is therefore an important benchmark for many packaging applications

## What OTR is necessary for what food packaging application?

To answer this one must know more about the packaged good. There are 2 different ways of calculating the necessary OTR:

- Either one knows the maximal allowed oxygen volume in the package
- or one knows the maximal allowed mass fraction of oxygen in the package.

Tab. 1: Oxygen ingress limits for different types of food with values from R. B. Armstrong, “Effects of polymer structure on gas barrier of ethylene vinyl alcohol (EVOH) and considerations for package development,” in Tappi Place Conference 2002.

Type of food | Maximal oxygen ingress in mass-ppm |
---|---|

Canned milk, meats, fish and poultry | 1 - 5 |

Beer, ale, wine | 1 - 5 |

Canned vegetables, soups, spaghetti, catsup, sauces | 1 – 5 |

Canned fruit | 5 – 15 |

Dried foods | 5 – 15 |

Carbonated soft drinks | 10 – 40 |

Fruit juices, drinks | 10 – 40 |

Oils, shortening | 50 – 200 |

Salad dressings | 50 – 200 |

Peanut butter | 50 – 200 |

Jams, jellies, syrups, pickles, olives vinegar | 50 – 200 |

**OTR evaluation chart**

With the knowledge from Tab. 1 all one needs to know to calculate the necessary OTR is

- The surface area
*A*of the package in cm² (excluding the area that has already a barrier, e.g. by an aluminum blister) - The mass
*m*in grams of the food that should be packaged - The type of the food
- The desired shelf life
*t*in days - Fig. 1, where
*K*is defined as*K*=*m/A*in g/cm². - That the temperature
*T*during the OTR measurement is normed at 23°C = 296 K.

For details how Fig. 1 was derived see this article.

**An example**

We assume that

*A*= 150 cm²,

*m*= 200 g and thus

*K*= 1.33 and that the food is a jelly. So one takes a limit for jellies from Tab. 1: ≈100 ppm. The desired shelf life should be

*t*= 200 d. Looking at Fig. 1 for the line for 100 ppm gives an OTR of about 3.8. Multiplying with

*K*gives an OTR of 5.1 cm³/m²/d.

So for a shelf life of 200 days one needs an OTR of 5.1 or smaller.

**Note:**The OTR for packages is measured against air. At the beginning of the measurement the package is free of oxygen and outside is air. The OTR of foils is in contrary measured against pure oxygen. Therefore OTR values for foils are given in the unit cm³/m²/d/bar while OTR values for packages have the unit

cm³/m²/d/air or cm³/m²/d/0.21bar.

## How does the oxygen level increase in the package?

Even if one does not know at which oxygen level the food taste will change, it is of interest how the oxygen level changes in the package.

This calculation of the oxygen level in the package

where

For details how formula (1) was derived see this article.

This calculation of the oxygen level in the package

*F(t*) can be done with the value of the measured OTR:where

*A*is the permeable area in m² of the package where O2 can diffuse in,*t*the time in days,*Vp*the package volume in cm³,*pA*the pressure outside the package,*p0*the pressure in the package at the start and Δ*pm*the pressure difference during the measurement of the OTR.For details how formula (1) was derived see this article.

**Important note:***If the package is stored at another temperature than the 23 °C usually used for the OTR measurement, one needs to measure the OTR also at this temperature! A recalculation the OTR to another temperature not possible.***An example**

It is known that the packaged food will change its taste if the O2 volume in the package reaches 5%. One has

*A*= 0.06 m²,

*VP*= 450 cm³,

*p0*= 0.01 (1% O2 in the package at the start). The OTR be 1 cm³/m²/air/day so it was measured at Δ

*pm*= 0.21 bar. With formula (1) one can calculate that after

*t*= 365 days the oxygen level is

Formula (1) can also be used to calculate that the maximal OTR is 1.44. Then

*F*(356) = 0.05 = 5%.