Modeling facilitates shelf life packaging.

As you know, many raw materials, semifinished and finished products are subject to change while in storage, leading to possible adverse effects on their quality. These could range from minor sensory off-flavors to complete spoilage. The shelf life of a product is influenced by its packaging. However, maximum packaging protection is not usually the most cost-effective solution. This approach may not meet environmental requirements, or it may be inconvenient for the consumer.

It makes more sense to design packaging not for maximum product protection but to achieve a defined shelf life. Scientists at the Swiss Federal Institute of Technology (Institute of Food Science, CH-8092 Zurich, Switzerland) have found that a packaging system with a specific shelf life in mind can be implemented using computer-aided simulation.

A food's quality involves physiological parameters of nutritional value and wholesomeness, and color, flavor, taste and texture. A decrease in food quality and a reduction in shelf life can affect one or more of these properties. One of the challenges involved in developing a proper package is to achieve the necessary barrier effect for a given shelf life.

The Swiss researchers assume that the packaging provides complete protection against the invasion of parasites, insects and microorganisms. They do not take into account the need to protect a food product against mechanical damage from breakage. The consideration of barrier effects may then be limited to a package's permeability to water vapor and gases, such as oxygen, carbon dioxide and nitrogen, and transparency to light. Permeability to flavor compounds could also be considered.

It is theoretically possible, with a given packaging material, to influence the changes and reactions controllable by moisture content or water activity; partial pressure of oxygen, carbon dioxide, or nitrogen; and the influence of ultraviolet radiation and sunlight. It may be possible to determine the shelf life for given barrier properties if we know the kinetics of the changes as a function of these factors and temperature. The necessary barrier properties for a specific shelf life also can be specified. Generally, such calculations can be used to come up with recommendations for packaging materials, packaging dimensions, filling, closure and storage conditions.

Swiss scientists modeled a variety of food products, including snack foods, lettuce, potato flakes, cereals and processed cheese. They used commercial software and included a database of various barrier values for water vapor, several gases, films, laminates and packages. They selected calculation modules after specifying the packaging. Data on total package volume, headspace volume, fill weight and filling conditions also were required. The program calculated development of critical quality factors of a food iteratively, and development over the proposed storage time was graphed.

Despite a lack of sufficient kinetic data for many quality deterioration reactions, generally the calculations performed agreed well with lab tests. Scientists still have to develop additional calculations for complex food systems that are difficult to characterize. They haven't included the influence of light in the software. Studies continue to obtain the needed data on the influence of light and ultraviolet radiation.

Further information. Felix Escher; phone: [phone]; fax: [phone]; email: [e-mail].