Preface
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VAST DEVELOPMENT OF NEW PACKAGING MATERIALS with a broad range of uses has occurred since 1987. In addition to protecting food products, packages now often serve as cooking containers. The combination of new materials and new uses for packages has resulted in previously unrecognized interactions between foods and the packages containing them. Food-packaging interactions can occur in a number of different ways. Components of the package can move into the food, a phenomenon that is called migration. Food components may also be absorbed by the package, and when the package absorbs flavor compounds the process is called scalping. The package may also influence or induce reactions in foods. An understanding of the permeability of packaging materials is important when selecting materials to provide adequate moisture, oxygen, and aroma barriers. Susceptor packaging, which contains specialized material that heats in a microwave oven to temperatures that will help products to brown and crisp, has received considerable attention in the past few years. Although there has been no health concern about this type of packaging, microwave suseptors have been researched extensively to confirm their safety and to provide information for the development of appropriate regulations. A significant portion of the symposium upon which this book is based covered the research that deals with susceptor packaging. This book probably provides the most comprehensive and current information in the field of food-packaging interactions all in one publication. This volume can serve as a resource for food product development scientists and packaging engineers who need to understand what can happen to foods in different types of packages. Regulatory agencies can also use this book to keep pace with new developments and to maintain appropriate regulations.
xi Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
We thank all of the authors who contributed their time and energy to make this book possible. SARA J. RISCH
Golden Valley Microwave Foods, Inc. 6866 Washington Avenue South Eden Prairie, M N 55344 JOSEPH H . HOTCHKISS
Downloaded by 80.82.77.83 on May 27, 2018 | https://pubs.acs.org Publication Date: September 13, 1991 | doi: 10.1021/bk-1991-0473.pr001
Institute of Food Science, Stocking Hall Cornell University Ithaca, NY 14853 June 28, 1991
xii Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
Introduction
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PACKAGING,
NOW AN INTEGRAL
PART OF THE FOOD
CHAIN,
has gone
from simply being a convenient container to hold and cany food to highly specialized systems serving many purposes. Many packaging materials still are little more than carrying containers that serve as dust covers to protect food from outside contamination. The demand for convenience and quality in food products has been accompanied by the development of packaging materials to help extend the shelf life of products; to provide barriers to moisture, aroma, and modified atmospheres; and to serve as cooking containers in both conventional and microwave ovens. Plastics, which can be one specific material (homopolymers) or a combination of materials (copolymers) and which can be laminated or coextruded, make up a large percentage of new packaging materials. Other packaging materials include paper or foil laminated to plastic film and tied together by adhesive layers. Various combinations of these materials can be used to meet the requirements of specific food products. Glass, which provides barrier properties, allows the preservation of food, and can also serve as a cooking container, was one of the first food containers. For packaging purposes, glass is considered virtually inert, that is, it does not interact with or change the characteristics of the food with which it comes into contact. This is not always the case with newer packaging materials such as plastic, paper, and paperboard. These new materials can interact with food products in a variety of ways. Permeability of these materials to various food components is one area of interest. Plastic overwraps or laminations are often used either to keep moisture in a product or to prevent the product from picking up moisture from the surrounding atmosphere. In addition to being a moisture barrier, the package may also serve as an aroma barrier to help retain flavor in foods and to prevent the absorption of undesirable flavors
or aromas. Although package permeability may result in flavor loss, an area that has received considerable attention is the absorption of flavors or specific flavor components by packaging materials. Flavor compounds tend to have low molecular weights and, as a result, not only pass more readily through plastic films but are also soluble in the polymers from which the films are made. This loss of flavor to the packaging is known as scalping. Individual compounds that make up a flavor can be selectively sorbed from a food product, with different compounds absorbed by the package to different extents. For example, 5% of compound X may xiii Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
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be absorbed while 30% of compound Y is absorbed. The result is both an unbalanced flavor in the product and an overall decrease in flavor intensity. A number of aspects of flavor scalping can be investigated. One area of interest is the relationship between a given type of film and a wide variety of flavor compounds to determine how the flavor of a product might change if put in contact with that particular polymeric structure. Another approach is to look at a particular class of compounds, for example, aldehydes or acids, and to determine how that particular class interacts with a variety of different films. Molecular weight and boiling point are properties that can influence the rate or extent to which flavor compounds are adsorbed by packages. Studies of scalping will help to determine the types of plastic films best suited for particular food products. Although some films may be adequate moisture or gas barriers for a product, that benefit can be offset by scalping. Flavors may be reformulated to compensate for selective loss of flavor compounds into the package, but the rate and extent of flavor loss, and the point at which an equilibrium is reached between the amount of a compound in the food and in the package must be known for reformulation to be successful. Components of the packaging material may also migrate from the package into the food. This is of concern for both the organoleptic quality and the safety of the food. When polymers for plastic films and packages are produced, complete polymerization of the monomers or starting units, although technically possible, it is not economically feasible. Incomplete polymerization results in residual monomers or oligomers in the finished materials. For example, residual styrene may be present in polystyrene, and the cyclic trimer may be present in poly(ethylene terephthalate). In addition to the monomers and oligomers, many materials may contain small percentages of other low-molecular-weight compounds that are often referred to as processing aids. A number of different types of compounds, including phthalates, are added as plasticizers. These plasticizers promote flexibility in the film and make the film easier to process. Some polymerization reactions require initiators or catalysts. Other compounds may be added to plastics to improve the strength, color, or other properties of the package. All of these low-molecular-weight materials are capable of migrating into the food with which they come into contact. This is an active area of study to ensure the wholesomeness of food products in these various packages. In the United States, extensive regulations that cover most existing packages and their intended use are outlined in the Code of Federal Regulations. As new materials are developed and new applica-
xiv Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
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tions are found for existing materials, further research must be performed to confirm the safety of the food packaging. As was previously mentioned, the migration of low-molecular-weight compounds can also impact the organoleptic quality of the food. Some compounds that migrate may not pose a health risk, but they may create an off flavor in the food. Therefore, packages must be screened not only from a safety standpoint but also from the standpoint of the sensory quality of the food. One development that has received considerable attention during the past few years is the microwave susceptor, which is a package developed to help meet the demands of convenience and quality in microwaveable food products. A susceptor is typically a piece of polyester film that has been metallized with aluminum. This material will interact with microwave energy to heat rapidly to temperatures in the 400 °F range. Susceptors promote browning and crisping of products in the microwave oven and help popcorn to pop more efficiently. The susceptor is laminated either to paperboard or between two layers of paper. All of the materials used in susceptor packaging meet existing regulations; however, the existing regulations were designed for usage conditions where much lower temperatures were anticipated. Although there have been no health or safety concerns, susceptor packages have been studied extensively to determine if new regulations are necessary and, if so, what regulations would be appropriate. Materials that can withstand the higher temperatures encountered in a conventional oven and still perform in a microwave oven are also being studied. These materials must also be evaluated to ensure that they do not create off flavors in foods and that package components do not migrate into the food. These are some of the more significant areas being studied in the field of food-package interactions. As new packaging materials are developed and new uses are found for existing materials, research into the safety and effectiveness of food packaging will continue. SARA J. RISCH
Golden Valley Microwave Foods, Inc. 6866 Washington Avenue South Eden Prairie, MN 55344 June 28, 1991
xv Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
