Food and Packaging Interactions - ACS Publications - American

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Chapter 21

New Packaging for Processed Foods

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Opportunities and Challenges Michael E. Kashtock National Food Processors Association, 1401 New York Avenue, NW, Washington, DC 20005 Packaging in a Changing Food Industry One of the most noticeable evidences of change in the processed food industry today involves the new forms of packaging that have begun to appear on store shelves. The universe of these new structures is characterized by terms such as retortable, dual ovenable, microwavable, aseptic, hi-barrier, co-extruded, etc. (1). To the consumer they offer convenience and quality attributes in step with modern lifestyle expectations and demographic factors. Consequently, the food processor must meet the challenges of these new technologies to prosper, and whoever does this well, may determine who remains viable in today's increasingly competitive marketplace. Not so long ago packaging choices for processed foods were relatively few. Retorted and hot filled products were available in cans and glass containers of varying sizes. Frozen items were available in boil-in-bag type pouches and foil trays. These packages were proven performers and played an important role in building and maintaining the confidence of the American public in the safety and quality of processed food products. However, the former state of affairs has given way to an array of new packaging choices for processed food products, and to understand why this is happening, one must consider the driving forces behind these changes. Economic factors have led the industry to pursue the use of lighter weight and unbreakable packaging materials in the interest of reducing shipping costs and liability risks. Perhaps the most visible success story in this regard has been the conversion of larger size carbonated beverage bottles from glass to polyethylene terephthalate (PET) over the last decade. This trend is continuing (with the additional driving force of user convenience) with the development of squeezable plastic barrier bottles for condiment items such as catsup, jelly, mayonnaise, relishes, toppings and sauces. The extremely successful 1983 market introduction of Heinz' catsup in a squeezable blow molded barrier bottle led the movement in this direction. 0097-6156/88/0365-0284$06.00/0 © 1988 American Chemical Society

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I t i s generally agreed by industry marketing experts that demographic trends have resulted i n an increases i n the numbers of dual wage earner households, households headed by one wage earning parent, and households without children (either comprised of young career types or senior c i t i z e n s ) . These developments have created an increasing demand f o r conveniently prepared food products, because i n many such households time i s at a premium. One a l t e r n a t i v e f o r the time pressured meal server i s the t r a d i t i o n a l stop at the f a s t food restaurant on the way home from work. Supermarkets are also competing f o r the convenience business with the advent of the pre-prepared food section where items such as soups and entrees can be purchased i n a microwavable container f o r quick and convenient reheating at home. Food processors are now also entering t h i s market with an array of frozen, r e f r i g e r a t e d and shelf stable products designed f o r fast heating i n the microwave oven (often i n the r e t a i l container) and convenient serving and cleanup. For frozen dinner and entree products, t h i s has l e d to a major s h i f t away from the t r a d i t i o n a l f o i l tray to microwave compatible p l a s t i c based structures. Trays fabricated from c r y s t a l l i z e d polyethylene terephthalate (CPET), thermoset polyesters and polycarbonate based coextrusions have been very successful i n f i l l i n g t h i s niche (2-4). These types of structures have the a d d i t i o n a l advantage of being able to be heated i n the conventional oven and are thus termed "dual ovenable." Shelf stable (retorted) items are also beginning to compete i n t h i s category. They o f f e r extremely rapid heating i n the microwave oven and s u r p r i s i n g l y high q u a l i t y , because t h e i r low p r o f i l e tray type packaging reduces the amount of thermal processing required to achieve commercial s t e r i l i t y . Packaging of t h i s type must have s u f f i c i e n t oxygen b a r r i e r f o r a one to two year shelf l i f e at ambient temperature, must be compatible with the processing environment of a retort and must maintain seal i n t e g r i t y during processing and d i s t r i b u t i o n ; a tough challenge. Coextruded b a r r i e r containers u t i l i z i n g ethylene v i n y l alcohol or SARAN (copolymers of vinylidene chloride produced by Dow) as the b a r r i e r material are currently the leaders i n t h i s area (5.), but newer b a r r i e r constructions are under development, with one, SELAR PA, an amorphous nylon, produced by Dupont, capable of being formed i n t o monolayer containers. The microwave oven i s one factor i n t h i s convenience driven market f o r new packaging whose importance cannot be overstated. I t i s currently i n use i n about 55% of U.S. households, with t h i s figure expected to r i s e to 80% by 1990. L i f e s t y l e changes are also playing an important r o l e i n the changing face of food packaging, The importance of high q u a l i t y to contemporary consumers has l e d to the development of many so c a l l e d "upscale" products ranging from premium frozen entrees and dinners to microwavable i c e cream sundaes. Packaging f o r such products must promote the q u a l i t y image the product seeks to project. For a frozen dinner f o r instance, t h i s might dictate the use of an a t t r a c t i v e "table ready" tray that has the appearance of dinnerware on the table (_6). Another challenge to be met. Extended s h e l f l i f e refrigerated products such as pasta salads, entrees and f u l l dinners are also now beginning to appear i n t h i s

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

FOOD AND PACKAGING INTERACTIONS

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q u a l i t y driven category. They often feature controlled or modified atmosphere packaging used i n combination with other control factors (see below) to achieve t h e i r extended shelf l i f e . For example, General Foods CULINOVA dinners currently i n test market, are refrigerated controlled atmosphere packaged meals with a dated shelf l i f e of three to four weeks (7). Such products as these o f f e r minimal preparation time i n the microwave oven and appeal p a r t i c u l a r l y to the consumer's perception of refrigerated products as a high q u a l i t y product category. Aseptic packaging i s a technology wherein the product and package are separately s t e r i l i z e d , and the product i s then f i l l e d into the package and the package sealed i n a s t e r i l e environment. The product i s commercially s t e r i l e (meaning that any pathogenic or other spoilage microorganisms have been destroyed) and shelf stable (does not require r e f r i g e r a t i o n or freezing). The emergence of aseptic packaging i n the U.S. represents an example of many of the above c i t e d d r i v i n g forces operating together. Economic savings are r e a l i z e d i n many cases by the use of l i g h t e r weight packaging materials such as polymer/foil/paper laminations or coextruded container constructions (8). Many aseptic packaging systems are based on f o r m / f i l l / s e a l technologies that eliminate the need to ship preformed containers to the processor. The processor receives sheet or r o l l stock at h i s plant which ships more densely and at less cost. The lightweight nature of these materials also r e s u l t s i n reduced shipping costs f o r the finished product. Convenience i n the aseptic product category i s offered by products such as snack puddings and dips i n EZ open thermoformed containers, and the f a m i l i a r s i n g l e serving juices i n b r i k s t y l e containers with the punch through attached straw; Instant snacks and lunchbox items f o r busy parents to serve. Higher product q u a l i t y may r e s u l t from the use of u l t r a high temperature (UHT) processes f o r aseptic products, because these usually r e s u l t i n less heat induced loss of product q u a l i t y versus processes that heat the product i n i t s container. Aseptic packaging i s now spreading from predominantly f r u i t juices into other product categories such as soups, gravies, baby food, tomato sauce, dairy drinks and yogurt (9.). Package Requirements I t i s evident that packaging i s playing an enhanced r o l e i n bringing products to the consumer that are i n keeping with today's marketplace demands. However, beyond understanding the market driven changes a f f e c t i n g food packaging, one should appreciate that packaging plays a c r u c i a l r o l e i n d e l i v e r i n g a safe and wholesome product to the consumer. The major packaging challenge facing food processors today i s to assure that package related factors that a f f e c t the microbiological and chemical i n t e g r i t y of food products are understood and controlled i n the production, d i s t r i b u t i o n and handling of products whether they be frozen, refrigerated or shelf stable (aseptic or retorted). Frozen products r e l y on freezing to retard microbial growth and chemical degradation. The package i s not generally c a l l e d upon to

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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form a microbial or gas barrier around the product. I t s p r i n c i p a l function i s to physically protect the product under the s t r e s s f u l conditions of frozen d i s t r i b u t i o n and sale. Also, i f the product i s intended to be cooked i n i t s r e t a i l container, the package must not chemically adulterate the product through the migration of toxic or off flavor components from the package during the cooking process. Of course, the l a t t e r applies for any food product type that i s processed or cooked i n i t s r e t a i l container. Extended shelf l i f e refrigerated products u t i l i z e refrigerated d i s t r i b u t i o n , usually i n combination with other factors (such as control of pH, water a c t i v i t y package gas composition, use of chemical preservatives and p a r t i a l processing) to retard microbial growth and chemical degradation, and thus achieve an extended shelf l i f e . Such products are l i k e l y to be marketed as premium products from which the consumer expects a high degree of quality. A successful package f o r this type of product must be capable of maintaining the controlled or modified atmospheric composition selected for the product, p a r t i c u l a r l y i f such control i s c r u c i a l to the microbiological safety of the product. Much attention and research i s now being focused on psycrotropic pathogens, a category of microorganisms of concern i n regard to this type of food product (10). As more i s learned about the factors that control t h e i r growth i n food media under refrigerated d i s t r i b u t i o n conditions, packaging may play an increasingly important role i n assuring the quality and safety of such products. Shelf stable products are rendered commercially s t e r i l e by heating the product to achieve the destruction of pathogenic microorganisms either: 1) within a sealed container, or 2) separate from the container followed by aseptic packaging of the product. S t e r i l i z a t i o n of the container may be accomplished by treatment of the container with heat, a chemical s t e r i l a n t (e.g., hydrogen peroxide), i o n i z i n g radiation or combinations of these. The package for any shelf stable product must constitute a microbiological barrier to the exterior of the container. Maintenance of the product's commercial s t e r i l i t y depends upon t h i s . If the product's commercial s t e r i l i t y i s compromised through a breach i n the package's i n t e g r i t y , spoilage of public health significance could result depending on the type of microbial contamination that occurs, the nature of the product and the environment within the container. Because of the potential r i s k s involved, the issue of package i n t e g r i t y for shelf stable food products i s probably the most intensely scrutinized and cautiously approached challenge associated with new packaging technology i n the food industry. Challenges to be Met This section w i l l address i n more d e t a i l some of the important package related factors that affect the microbiological and chemical i n t e g r i t y of packaged food products. From a food processors perspective these are factors that must be understood and controlled to assure the safety and wholesomeness of processed food products.

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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Seal I n t e g r i t y . Seal i n t e g r i t y i s c r i t i c a l to assuring the safety of shelf stable products. Many new p l a s t i c container types u t i l i z e heat to seal a l i d to a container body (or to seal the container i t s e l f i n foldover fashion). Heat sealed containers may employ a peelable or fusion (non-peelable) seal. The l a t e r , which w i l l generally result i n a greater seal strength, can be u t i l i z e d on packages such as retortable pouches where the package i s not opened by peeling at the seal area. Peelable seals are being developed f o r convenience oriented products, many of which are intended to be heated and served i n their r e t a i l container, such as microwavable ready to serve soups. These seals are generally designed to be opened by peeling them back from the container flange. For such an application to be successful, this should be able to be done by the average consumer as opposed to the household "Lurch" who i s called upon to open the pickle j a r . A challenge that must be met i s the development of l i d d i n g systems employing a combination of materials and sealing parameters (dwell time, seal pressure, seal temperature) that w i l l result i n p e e l a b i l i t y and yet maintain seal i n t e g r i t y under the stresses associated with retorting, d i s t r i b u t i o n and handling. Packaging material converters are developing such lidstock materials at the present time. Several products are now i n test market i n the U.S., with larger scale commercialization anticipated i n the near future. Standard peelable f l e x i b l e l i d d i n g constructions are generally laminated structures with a f o i l barrier layer, polymeric inner (food contact) and exterior layers, and appropriate adhesives. A new and somewhat d i f f e r e n t approach to l i d construction recently introduced by the Continental Can Company on i t s MENU BOX container, u t i l i z e s a semi-rigid coextruded barrier sheet fabricated with an i n t e g r a l p u l l tab. The l i d i s fusion sealed to the container flange and undergoes separation at a material interface within the coextruded sheet when the tab i s pulled. Continental Can reports that the t e n s i l e strength and seal strength of this structure s i g n i f i c a n t l y exceed those of standard f l e x i b l e l i d s t o c k s . No l i d d i n g / s e a l i n g concept i s right for every packaging application. Factors that should be considered i n choosing a packaging system include the type of product, i t s intended processing, the type of secondary packaging to be used, and the rigors of the d i s t r i b u t i o n system. A thorough approach to assessing a package's seal performance would include performing simulated abuse testing and t r i a l d i s t r i b u t i o n shipments on commercial units ( i . e . , p a l l e t i z e d shipping u n i t s ) , followed by an examination of the seal and the entire package (11). Processors should also have an ongoing quality control program for seal evaluation of finished containers prior to commercial shipment. Weak or incomplete seals can result from causes such as sealing head pressure or temperature drops, inadequate sealing dwell time, head misalignment, or product contamination on sealing surfaces ( 12). At the present time many processors i n test marketing programs are relying on 100? v i s u a l inspection of container seals, and some even hold the product f o r incubation followed by a second examination before shipment. Line samples of finished product should also be p e r i o d i c a l l y pulled f o r seal evaluation by a destructive technique such as burst testing (or dye

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penetration or electroconductivity testing for aseptic brik type containers) (13)» This documents the continuous performance of the sealing system within preset parameters. Reliance upon manual visual inspection techniques w i l l probably not s u f f i c e to handle commercial scale volumes of product. Automated systems are currently under development and evaluation that w i l l provide f o r on-line high speed non-destructive seal testing. For example, one system, developed by Benthos Inc., operates by pressurizing a container's seal area and e l e c t r o n i c a l l y monitoring for any deflection of the l i d , which be i n d i c a t i v e of a possible leak into the container from the seal area. An industry committee (Flexible Package Integrity Committee) of the National Food Processors Association i s scheduled to publish an i n t e g r i t y b u l l e t i n for certain types of f l e x i b l e and semi-rigid packages i n 1987. I t w i l l contain photographic i l l u s t r a t i o n s of container defects with c l a s s i f i c a t i o n of the defects into the categories of c r i t i c a l , major, and minor, for heat sealed and double seamed p l a s t i c containers, retortable pouches and paperboard based containers used for aseptic packaging. This publication w i l l be useful to personnel involved i n container inspection and w i l l serve as a f i r s t l i n e sorting guideline for p o t e n t i a l l y defective containers prior to laboratory examination. I t w i l l also prove useful to personnel engaged i n package development. Another NFPA committee ( P l a s t i c Packaging Lab Methods Committee) i s assessing the r e l a t i o n s h i p between the manner i n which destructive container testing i s conducted and the results obtained. For instance, i n burst testing, factors such as the rate of internal pressure increase i n the container and the manner i n which container expansion i s restrained, influence test r e s u l t s . Data of this type generated f o r internal use or f o r submission to regulatory agencies should be based upon test procedures that minimize the effect of test variables. Influence of the Retort Environment. The use of f l e x i b l e and semir i g i d container types i n retort applications requires an understanding of retort induced effects that may a f f e c t process adequacy and package i n t e g r i t y . For example, containers build up internal pressure i n a retort to an extent that depends upon factors such as the type of product, pre-processing treatments (blanching), the amount of entrapped gases in the product and the temperature within the container (14). I f internal container pressure d i s t o r t s the shape of the container during processing, the adequacy of the thermal process could be affected. In addition, excess internal container pressure could place undue stress on the heat seal. In retort systems, overpressure, provided by a i r , steam or steam/air mixtures i s applied to prevent container deformation, and represents a c r i t i c a l process f a c t o r . Because of the complex and c r i t i c a l nature of process related parameters, processors w i l l generally c a l l upon a recognized process authority to design and evaluate a thermal process i n the product development stage. The process authority w i l l also a s s i s t the processor i n any required regulatory f i l i n g of the process.

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FDA regulations require that thermal processes for a c i d i f i e d and low acid commercially s t e r i l e foods be f i l e d with the agency prior to packing the product, while the USDA's proposed canning regulations require that processes be maintained on f i l e for the agency's inspection upon request. The United States Department of Agriculture i s responsible for the regulation of meat and poultry products while the Food and Drug Administration i s responsible for a l l other a c i d i f i e d and low acid product types. Aseptic Systems. In a commercial aseptic packaging operation for low acid foods, i t i s of c r i t i c a l importance that the operator control system parameters that affect package s t e r i l i t y and i n t e g r i t y . Aseptic packaging equipment must be thoroughly tested before commercial operation to assess the system's design and the performance of the s t e r i l i z a t i o n , f i l l i n g and sealing operations. The techniques for evaluating the equipment are quite sophisticated and involve inoculating the packaging material and the equipment i t s e l f with selected test organisms, followed by actual packing of test product. The product i s then microbiologically evaluated to demonstrate that product s t e r i l i t y was achieved under operating conditions (15). As with retorted products, government regulations require process f i l i n g and the validation of process adequacy for aseptic packaging equipment. Here also, processors generally seek the assistance of a recognized process authority i n performing system evaluations. Chemical Considerations for Packaging Materials. Under Section 201(s) of the Federal Food, Drug and Cosmetic Act (the Act) food packaging materials are defined as food additives (when they may be reasonably expected to become a component of the food), and must, i n accordance with Section 409 of the Act, be l i s t e d prior to use, i n the Code of Federal Regulations, i n a food additive regulation specifying conditions for safe use (Note: there are some exceptions pertaining to generally recognized as safe (GRAS) substances and prior sanctioned substances that are covered i n Dr. Breder's presentation i n this symposium). Such a l i s t i n g usually occurs i n response to the submission of a food additive p e t i t i o n establishing the safety of the proposed use. Provisions i n the food additive regulation may l i m i t use of the packaging material to contact only with certain types of foods, or impose a maximum food contact temperature. The regulation may also establish certain s p e c i f i c a t i o n s for the packaging material. Compliance with the applicable food additive regulation w i l l l a r g e l y ensure the safety of a given use of a packaging material. However overriding the food additive provisions of the Act i s the so called general adulteration clause i n Section 402 of the Act, under which any p o t e n t i a l l y harmful substance i n a packaging material can render i t adulterated, even i f the material f u l l y complies with the applicable food additive regulation. For instance, residual impurities i n substances used i n the manufacture of a polymer, i f such residues are carcinogenic or cause an o f f - f l a v o r or odor i n the food, could render the packaging material adulterated. The food additive regulations state what the

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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chemical i d e n t i t y of the polymer must be, but usually do not stipulate how the polymer must be made, or what the degree of purity of the s t a r t i n g materials must be. Therefore, the method of manufacture of a resin as per the catalyst and solvents used, i t s curing and drying etc., has implications as to whether the r e s i n i s acceptable as a food grade packaging material, even i f the resin f u l l y complies with the applicable food additive regulation. In this connection, some processors are electing to screen prospective packaging materials for v o l a t i l e substances that may be cause f o r t o x i c i t y or o f f - f l a v o r concerns using methods such as gas chromatography/mass spectrometry. Some are asking for more rigorous validation of l e t t e r s of guarantee from their suppliers concerning the regulatory compliance of the supplier's packaging materials. Users and suppliers of packaging materials should have a mutual understanding as to what constitutes an acceptable packaging material for a given application. Processors whose products w i l l be processed or cooked i n t h e i r r e t a i l container should also assure themselves that excessive migration of the container material does not occur at elevated food contact temperatures. Many of the existing food additive regulations for packaging materials predate the use of p l a s t i c containers as processing and cooking vessels, and do not contain upper use temperature l i m i t s , so the s u i t a b i l i t y of a container for any application involving thermal processing, hot f i l l i n g , or home heating i n container should be c a r e f u l l y evaluated. Such product/package interaction i s l i k e l y to be product type dependent and may be assessed by conducting extraction studies with food simulating solvents or by sensory evaluation to ensure that the food i t s e l f does not taste l i k e the package. On the regulatory developments front, the FDA i s currently developing a threshold of regulation policy that i s intended to define conditions under which certain packaging materials may be used without requiring a formal food additive regulation (16). Such a situation would involve uses where the extent and nature of migration i s such that i t could be considered i n s i g n i f i c a n t from a regulatory standpoint. This e f f o r t i s of particular interest to packaging suppliers and users because i t may ultimately eliminate the food additive p e t i t i o n requirement for certain package components such as new barrier materials used i n coextruded structures, expediting t h e i r a v a i l a b i l i t y to the industry. S t e r i l a n t s Used for Aseptic Packaging. In aseptic packaging applications the treatment of the packaging material with chemical or physical s t e r i l a n t s (e.g., i r r a d i a t i o n ) also has implications concerning the food additive regulations. I f a proposed s t e r i l i z i n g treatment could conceivably modify a regulated packaging material i n such a manner that i t no longer complies with the food additive regulation f o r the material, FDA could request data concerning such e f f e c t . I f such treatment were shown to modify the packaging material, then a separate food additive p e t i t i o n covering the proposed use would l i k e l y be required. In the absence of any s t e r i l a n t induced modification, the packaging material need only comply with the existing food additive regulation.

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However, there i s one important difference between the use of chemical s t e r i l a n t s and i r r a d i a t i o n concerning the food additive regulations. Chemical s t e r i l i z a t i o n of a packaging material i s l i k e l y to leave a residue on the packaging material which w i l l i t s e l f be subjected to clearance as a food additive (see the regulation for hydrogen peroxide i n 21 CFR 178.1005). On the other hand, because i r r a d i a t i o n of a packaging material separate from the food i s a physical process that does not leave a residue on the packaging material, there i s no requirement to submit a food additive p e t i t i o n f o r the package s t e r i l i z a t i o n process, provided the process has not altered the packaging material. I r r a d i a t i o n of a food within i t s package i s an e n t i r e l y different matter which would l i k e l y require a separate clearance unless the packaging material has already been cleared for such use under 21 CFR 179.45 (17). Conclusion Conquering the challenges of the new packaging technologies that affect food quality and safety, w i l l undoubtedly be major pursuits of the food industry i n the near and long term future. This paper has largely emphasized the safety aspects of this subject, as t h i s i s where many of the cooperative industry e f f o r t s coordinated by the NFPA have been concentrated. We are pleased to see some of the fine work directed at food quality and safety aspects being done at many of our academic i n s t i t u t i o n s , some of which was presented at t h i s symposium. In our opinion, some primary areas for ongoing research w i l l be: 1) ensuring the safety of food products that attain an extended shelf l i f e through the application of non-lethal processing and packaging technologies such as modified atmosphere packaging, 2) developing a better understanding of the factors that govern food quality and shelf l i f e and r e f i n i n g this understanding into better techniques for modeling shelf l i f e and accelerated shelf l i f e testing, 3) the evolution of packaging and products t a i l o r e d s p e c i f i c a l l y for use with the microwave oven. Aspects such as package design, construction and product formulation w i l l be engineered f o r optimum performance i n the microwave environment, and 4) establishing the safety of many food packaging materials for i r r a d i a t i o n of food i n the package. Such w i l l be required for FDA approval of new applications. Obviously, there i s much that a user of the new packaging technologies must understand. History has taught food processors that they cannot simply be "users" of this new technology, but must be informed and active users, continually seeking to learn more about the relationship of the package to the product. This i s why the food processors of the NFPA have made a commitment to u t i l i z e their resources i n cooperation with suppliers and with each other, to stay on top of the challenges that this new technology presents.

References 1. Packaging. January 1987, 32, 24. 2. Stras, J., Packaging, Encyclopedia. 1986, 31, 158.

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Foods

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Food Engineering. February 1986, 58, 38. Food Processing. January 1987, 48, 160. Packaging. December 1984, 29, 70. Packaging. November 1985, 30, 27. Packaging. A p r i l 1987, 32, 11. Milgrom, J . , "Cost Effectiveness of Various P l a s t i c Packaging Materials", Foodplas 84/85, P l a s t i c s I n s t i t u t e of America, Inc. Food Processing. June 1986, 47, 62. Scott, V.N., "Control and Prevention of Microbiological Problems i n New Generation Refrigerated Foods", Presented at 41st Annual Meeting of Research and Development Associates for M i l i t a r y Food and Packaging Systems, Inc., May 1985, Norfolk, VA. DiGeronimo, M.J., "Dynamic Testing to Predict Package Performance i n D i s t r i b u t i o n " , Packaging Alternatives f o r Food Processors, National Food Processors Association. Downes, T.W., "Q.C. Test Procedures f o r Seal Integrity", i b i d . Polvino, D.A., "Integrity Issues and Test Procedures for Semi-Rigid Retortable Containers", Presented at National Food Processors Association Annual Convention, February 1986, Atlanta, GA. Polvino, D.A., "Retortable P l a s t i c Containers Today: Technical Status", Proceedings of Foodplas IV/87, P l a s t i c s I n s t i t u t e of America, Inc. Bernard, D., Gavin, Α., Scott, V., Shafer, B., Stevenson, Κ., and Unverferth, J . , "Evaluation of Aseptic Systems", Presented at Annual Meeting of the I n s t i t u t e of Food Technologists, June 1986, Dallas, TX. Food Chemical News. February 10, 1986, 28, 71. Federal Register. A p r i l 18, 1986, 51, 13394.

RECEIVED September 24, 1987

Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.