Antimicrobial Additives and Coatings for Food Packaging

It seems as if every day we hear of some incident associated with food contamination. Recent outbreaks of contamination associated with meat products heighten consumer concerns.

To this end, food packaging engineers and scientists are investigating new ways to provide greater shelf life for packaging. Providing physical protection as well as moisture and oxygen barrier is a given. With today's quality demands, that may not be enough.

Packaging engineers are looking not only to extend the shelf life of their packaged foods but also to extend the quality and nutritional value of their food items. To this end, new technologies are being used to improve the internal atmosphere surrounding the food. Oxygen-scavenging materials and other antimicrobial additives promise that packages will absorb oxygen and prevent rancidity of the food.

What are antimicrobials?

Microbes that contaminate packaging materials typically are controlled by using heat, steam, or radiation, or by the addition of antimicrobial additives. Packaging antimicrobials are materials that can be added to packaging materials and will prevent microbial growth.

Among the most common antimicrobial materials are organic acids and their salts. Potassium sorbate, for example, is used commonly in PE packaging materials for cheese. Oxygen-scavenging systems, such as reduced iron complexes, absorb oxygen gas within the package and reduce oxidation of food components. Reduction of oxygen prevents growth of aerobic microorganisms, such as mold.

Flushing the product with selected gases can control mold growth. For example, gas rich in sulfite can prevent or delay fungi development.

Sulfites, nitrites, and low-molecular-weight alcohols have antimicrobial properties. Other materials include enzymes, preservatives, and sterilizing materials. Among these are peroxides, ozone, eugenol, nisin, and lysozyme. Many of these agents can be incorporated into the packaging materials and will migrate into the food through diffusion.

Balancing the antimicrobial release and its effectiveness not only is dependent on the packaging materials but the food chemistry as well. The pH, water content, oxygen availability, etc., provide different environmental conditions to microorganisms in the food.

Although most packaged food products are heat sterilized, microbial contamination can and does occur. Use of antimicrobial packaging offers a degree of protection and extends the shelf life of perishable food products.

Packaging engineers are busy designing the best configuration for specific antimicrobial materials. Many incorporate a multilayer structure for controlling antimicrobial release. The advantage of the multilayer design is that the antimicrobial can be added in one thin layer, and its migration and release are controlled by the thickness of the film layer or coating. In practice, a matrix of several layers is used to control the antimicrobial agent rate of release.

The application of antimicrobials to food packages can take several approaches. One is to put the antimicrobial into the film by adding it in the extruder when the film or coextrusion is produced. The disadvantage of doing this is that the high temperatures and shearing associated with the extrusion process can deteriorate the antimicrobial additives.

An alternative to extrusion or extrusion coating application of antimicrobials is to apply the antimicrobial additives as a coating. This has the advantage of placing the specific antimicrobial additive in a controlled manner without subjecting it to high temperature or shearing forces. In addition, the coating can be applied at a later step, minimizing the exposure of the product to contamination.

Today's food packaging not only should store the contents and shelter it from physical abuse; it should influence the freshness and taste and control the microbial activity. Antimicrobial substances help.

Dr. Richard M. Podhajny has been in the packaging and printing industry for more than 30 years. Contact him at 215/616-6314, e-mail: rpodhajny@colorcon.com.


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