Food and Packaging Interactions Affecting Food Quality

Abstract: Food and packaging interactions that may impair the food quality have been studied and methods to determine these interactions have been developed.

An off-line supercritical fluid extraction method using carbon dioxide was developed and used to extract sorbed low molecular weight compounds from polymer films. This method is quantitatively comparable to methylene chloride extraction, but faster and more environmental friendly.

Both external factors like humidity, and properties of the food itself (e.g. type and concentration of compounds) were found to affect the type and degree of interaction with the packaging material. The relative humidity (RH) was found to affect the permeation and sorption of aldehyde and alcohol vapours in both polar (EVOH) and unpolar (LLDPE and HDPE) polymers. The alcohols and aldehydes were affected in different ways. In the EVOH film the permeability of aldehydes increased with increasing RH while the permeability of alcohols was at a maximum at 50% RH. This difference is attributed to the different ability of the compounds to interact with sorbed water and the polymer and can be explained by also studying the sorption and diffusion of the compounds.

Sorption of vegetable oil into polyolefins (HDPE and PP) increased the oxygen transmission rate (OTR) through the polymers. After 40 days of storage in rapeseed oil, the OTR of a 40 .my.m HDPE-film was increased by approximately 40% compared to the OTR of the virginal polymer. The PP film was affected to a lesser extent.

As foods consist of a complex mixture of many compounds it is often necessary to use a simplified model system to study aroma/packaging interactions. The effect of the model system (i.e. gas/liquid state, concentration, and mixture of compounds) on the sorption data obtained was investigated. Hexyl acetate and ethyl butyrate in a liquid model system (40% ethanol) at a concentration of 50 or 1000 .my.g/ml, were sorbed to a lesser extent from a mixture of compounds than from a single compound solution. The use of single compound solutions may thus lead to overestimation of the amounts sorbed in an actual food packaging application. However, at low concentrations (i.e. 5 .my./ml), which could be found in foods, the compounds were found to be sorbed in the packaging material independently of co-sorbants. The aroma vapours were sorbed in amounts related to the feed concentration without any interactive effects of co-sorbants, in the concentration range (i.e. 0.12-3.4 .my.g/ml) and mixtures investigated.

In spite of the increasing use of refillable polymer containers for foods there is currently no standard test procedure to check the sorption and remigration of aroma or misuse chemicals into/from the packaging material. A test scheme for a cost and time-efficient inertness test for determination of the interactions between misuse chemicals or aroma compounds and refillable PET bottles was developed. Small strips of PET bottle walls in contact with a selection of model contaminants were used in the test.

This thesis shows the importance of studying the barrier properties of a polymer film under as realistic conditions as possible, taking into account both the storage conditions and the interactions between a food and the packaging material.