Reusing Food Packaging ... Is It Safe?

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Reusing

Food Packaging . . . Is It Safe?

DHT 2 8

AG Library

M. Susan Brewer

University of Illinois at Urbana-Champaign College of Agriculture Cooperative Extension Service Circular 1320A Helping You Put Knowledge to Work

Cooperative University of Illinois Extension at Urbana-Champaign Service College of Agriculture

This publication was prepared by M. Susan Brewer, Extension Specialist, Foods and Nutrition, Division of Foods and Nutrition, University of Illinois at Urbana-Champaign.

Edited by Francine Weinbaum Designed by Joan R. Zagorski

Urbana, Illinois July 1992 Issued in futherance of Cooperative Extension Work, Acts of May 6 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. DONALD L. UCHTMANN, Director, Cooperative Extension Service, University of Illinois at Urbana-Champaign. The Illinois Cooperative Extension Service provides equal opportunities in programs and employment.

.5M—7-92—1320A—fw Introduction How does our food get on the Many consumers reuse food pack-

table? Packaging is an essential aging because they are concerned component in the complex distri- with protecting the environment. bution system which moves agri- Recent years have brought in- cultural products from their point creased environmental pollution of origin to their point of con- and decreasing natural resources sumption. Along with our cul- and landfill space. But improper ture, our packaging of food has reuse of food packaging can threat-

become increasingly specialized en health. So it is important to and complex. Sterile boxes of follow certain guidelines (see

fruit juice, plastic food pouches page four). For example it is gen- that can tolerate pressure canning, erally safe to reuse glass that has and microwave-safe containers been used for food, but not to re- are but a few examples of special- use plastic or paper. Understand- ized food packaging which did ing the uses, specialized func- not exist twenty years ago. Food tions, and limitations of packag- packaging has several functions ing materials used for protecting

other than its primary one of pro- consumer foods can help consum- tection. Packaging protects food ers make safe decisions regarding from microbial and other environ- the reuse of packaging materials. mental contaminants, and from

damage during distribution. It This circular discusses the follow- also offers the consumer nutri- ing topics: tion and ingredient information, 1. commercial sterilization tech- cooking instructions, product niques that keep microbes out; weight, brand identification, and 2. glass, plastic, paperboard pricing. and packaging of food;

and includes

3. easy-to-follow guidelines for reusing food-packaging materials;

4. a glossary of food-packaging terms for the consumer who wants to take the time to become knowl- edgeable. Keeping Establishing microbiological sta- (which uses high temperatures for bility is of primary importance for very short times), and gamma ray Microbes Out most food products. Early food irradiation. The packaging mate- packaging had to be able to toler- rials used for these new processes ate heat so that the product could must be sterilized before they are be canned (terminally sterilized used; methods used to sterilize in the container). Glass and tin packaging include hydrogen per- cans were the original processed- oxide or steam treatments, expo- food packages because they could sure to ultraviolet light, or gamma tolerate sterilization temperatures. ray irradiation. A variety of foods Because food flavors are apt to are "hot-filled" at 170°F, so the change during heating, a variety chemically sterilized packaging of sterilization techniques have must be able to tolerate tempera-

been designed to kill or remove tures slightly above 170°F. Pack- microbes from food products us- aging materials that tolerate these

ing little or no heat processing. processes will not always tolerate These techniques include the use temperatures over 180°F without of hydrogen peroxide treatments, substantial breakdown. aseptic packaging (packaging in a sterile environment), ultra-high temperature (UHT) sterilization

Glass Most packaging materials are de- board are designed to be recycled signed for one use. With the ex- into new packaging forms that do Versus ceptions of glass containers re- not come into contact with food. quiring user deposit and limited- These recycled forms can be used Plastic and use polycarbonate bottles, manu- in outer layers of a food package Paperboard facturers assume that consumers or as containers for foods encased will take the product home, then in other materials. discard or recycle the packaging.

Packaging is designed accord- When manufacturers design a ingly. Packages are designed to packaging system, they consider tolerate the type of food system the type of food (high-acid versus

(acid, base, alcohol, or fat) that low-acid), the susceptibility of the will be contained within them. food to light and oxygen (milk,

No safety is implied for other food fruit juice), the amount of physi- systems or for reuse of that pack- cal protection needed (eggs), and age in ways not suggested for the the amount of product visibility original food product. In general, desired (fresh meats). They also

glass is the only packaging mate- consider the amount of heat to be

rial designed for reuse that uses

the packaging over again in its original form. Plastic and paper- used during sterilization, the con- ally layers of different polymers. the food product, a problem that tainer size, and the type of "home Each layer makes a contribution can be aggravated by heat and by processing" to which the product to total package performance. the presence of a food into which will be subjected (for example, the plasticizing chemical will dis- microwaveable pizza). Other con- Flexible plastics may contain solve (for example, oil, acid, or siderations include the cost and small amounts (1 to 2 percent) of alcohol). Migration of the com- availability of the packaging mate- other substances that perform pound increases with length of rial, the cost of transporting the specialized functions. These "ad- contact time and temperature, finished product (plastic versus ditives" include catalysts to aid in and levels of migration are high- glass soda bottles), recyclability the polymer formation reaction, est when there is direct contact (plastic versus paper), and con- antioxidants to prevent oxidation between film and foods with high sumer attitudes about packaging. of the packaging material, stabiliz- fat content at the surface. ers to prevent degradation of the

Most plastics are considered packaging material when it is The Food and Drug Administra- "high-barrier" packaging materi- heated or exposed to ultraviolet tion assesses the initial safety of als. They exclude moisture and radiation, and plasticizers. Plasti- packaging materials for food con- most gases (including oxygen), cizers increase the flexibility of tact. If substances are shown to and they can be either optically plastics. They intersperse around migrate from the packaging into clear or opaque. Because of their the polymer molecules and pre- the food, they are treated as "inci- unique characteristics, plastics vent them from bonding to each dental food additives" and toxico- are becoming the most important other so tightly that they form a logical studies are conducted in packaging material for food prod- rigid substance. Plasticizers may order to establish safety stan- ucts. The packaging industry is lower the melting point of the dards. The safe reuse of packag- the largest user of plastics; more plastic, and many have relatively ing materials has been studied than 90 percent of flexible pack- low melting points themselves. much less, but some generaliza- aging is made of plastics. There has been some concern tions can be made. about the migration of plasticizers

Plastics are produced from base out of the packaging material into polymers called "resins." Most actual packaging applications in- volve several types of resins. Structural polymers such as polyethylene (PE) and polypropylene (PP) provide mechanical properties (strength, rigidity, abrasion resistance) at low cost. Barrier polymers such as polyvinylidene chloride (PVDC) and ethylene vinyl alcohol (EVOH) provide protection against transfer of gases, flavors, and odors. Tie resins (adhesive resins) bond the structural and barrier resins together. Heat- seal resins provide package clo- sures in flexible packages. In fact, many "plastic" packages are actu- Guidelines 1. Packages from products other 4. Do not reuse porous packag- than food should never be used ing materials such as paper, for as food containers. They have paperboard, and expanded foams not been tested for safety with (for example, styrofoam cups and Reusing food systems, and they may con- foam meat trays). They have air Food-Packaging tain small amounts of nonfood spaces that will harbor food par- residues. (For example, do not ticles and microorganisms. Materials use plastic laundry detergent buckets for storing dry cereal.) 5. Do not reuse microwave packages that contain "heat suscep-

2. Glass can be reused for all tors" for browning or crisping.

foods and for all processes. This The adhesives that hold the

is true regardless of what food susceptor to the package may was originally packaged in the be damaged by the original use.

glass container. There is an ex- The material is more likely to mi-

ception to this rule: single-use grate into the food if it is used glass jars should not be used for again. pressure processing in the home

canner. The lid or cover, how- 6. It is better not to store foods

ever, is subject to recommenda- with strong odors or flavors in re-

tions discussed below (number 3). used food packages; the packaging material might absorb the 3. Reuse packaging materials chemicals that produce the odor only with the following: or flavor and release them into a subsequently stored product. Ad- • foods similar in acidity and ditionally, some packaging mate- in sugar, fat, or alcohol content rials allow certain chemicals to to the food originally packaged pass through them, transferring in the material. Do not use a odors or flavors to other foods plastic shortening container to stored in the same area. make salad dressing containing a substantial amount of vinegar.

• foods that will be exposed to the same types of processes. Do not melt butter in the microwave oven using a plastic mar- garine container. In general, do not subject food packages to heat unless the instructions on the original package give heat ing information. Many food products are "hot-filled" into containers at low temperatures. These packages will not tolerate heating. 7. When materials are safe for use 9. If you are using a flexible film 11. Use only "food-grade paper" in the microwave oven, they are bag like a bread wrapper for food in direct contact with food prod- usually labeled for such use. storage, always use it with the ucts. Paper processing uses a va-

If you do not know whether the printed side out. Printing inks riety of chemicals, and the raw material is safe for use in the may contain materials that are not materials can contain residues microwave, don't use it. Soft meant for human consumption. which would be unacceptable in plastics are especially likely to These inks may migrate into food foods. Paper products destined flake, blister, deform, and melt. if they come into direct contact for contact with food are manu-

This allows plastic polymer or with it. factured by processes which additives to penetrate into the minimize residues, and the fin- food. ished product is routinely tested. 10. If you store a nonfood item in a food container, do not reuse the 8. Suppose you are using a flex- container for food storage. Many ible plastic wrap to cover a con- plastics pick up small amounts of tainer of food are heating in you the substances stored in them and the microwave. Be sure to "tent" release them later. Motor oil the film over the food with tooth- stored in plastic milk jugs will picks. There should be no direct later be present in lemonade if contact between the film and the you store lemonade in the same food. Do not seal the contact edge container. between the film and the container. If you do, you may be burned by the steam that builds up during heating. This steam can escape rapidly when you remove the film. 6

A Glossary Food-grade plastics often have AN information embossed into the Acrylonitrile monomer. Usually, bottom of the container. The type of the term refers to acrylonitrile of plastic material may be referred that is polymerized with styrene Food-Packaging to by an acronym such as HDPE or methyl aerylate. AN films, or EVOH. Terms coatings, and semirigid containers are cleared for use only for single- ABS use food-contact surfaces. They Poly(acrylonitrile-butadiene-sty- have not been tested for use above rene) copolymer. Heat distorts it 120°F. AN films are used prima- at 200°F. Maximum continuous rily in the pharmaceutical indus-

service temperature is 165°F. ABS try.

is resistant to acids, bases, fats,

and oils. It does not resist sol- CA vents and yellows if exposed to Cellulose acetate. This material is sunlight. ABS has been cleared manufactured like cellophane, but for food use with all foods except there is an additional reaction those containing alcohol and that includes acetic anhydride. It those subjected to thermal pro- is easily deformed by heat, acids, cessing. It can be used with foods bases, and some solvents but is that are filled and stored at room resistant to fats and oils. It builds temperature, and stored refriger- up static. Maximum continuous ated or frozen. service temperature for CA is ATBC 175°F.

Acetyl tributyl citrate, a deriva- Cellophane tive of citric acid. ATBC is used Regenerated cellulose-based flex- in flexible packaging films and ible packaging material. Cellulose has been cleared for use as a plas- is dissolved in sodium hydroxide, ticizer for food contact surfaces of then extruded into an acid-salt resinous and polymeric coatings bath to produce filaments of re- and in paper and paperboard for generated cellulose. It can be use with fatty foods. It has been coated with Saran for use with sanctioned by the FDA and falls oily or greasy products. Cello- into the "relatively harmless" tox- phane was introduced in the icity category as a consumable 1920s as a bread wrap. It is semi- chemical. Estimated daily human moisture-proof and heat-sealable. intake from current uses of plastic The heat-sealing range is 200 to film is around 0.0008 milligrams 300°F. Cellophane is flammable. per kilogram of body weight.

ATBC is considered safe at this level. EVA 2. An ethylene content of 55 HDPE to 15 Ethylene-vinyl acetate copolymer. percent percent vinyl High-density polyethylene (see alcohol can be used with aque- EVA is a flexible packaging mate- PE). HDPE has a maximum con- ous acid and nonacid foods rial formed from low-density poly- tinuous service temperature of with free surface oil; dairy oil ethylene (PE) and vinyl acetate. It 160°F but distorts at 140°F. It is in water emulsions; beverages; is more flexible than PE but more resistant to moisture, gases, acids, low-moisture fats and oils; permeable to water and gases. bases, solvents, and fats and oils. moist bakery products and dry EVAs are unstable at high temper- It will build up static. HDPE is solids with free surface oil; atures but stable at low tempera- and used for milk jugs, cleaning sup- foods that are refrigerated or tures. EVA is cleared for use with ply bottles, and trash bags. frozen-stored fatty foods and for treatment with with no thermal irradiation as a sterilant (up to 8.0 treatment. High-oxygen-barrier megarads total), so it need not be 3. An ethylene content of 20 polymers heat-sterilized. It is very stretchy, to 40 percent, to 60 to 80 per Polymers used to prevent almost it can be as a shrink wrap. cent vinyl alcohol is so used approved all oxygen transfer. These materi- for food use with all foods ex- als include vinyl alcohol, vinyli- EVOH cept those containing alcohol dene chloride, and acrylonitrile. Ethylene vinyl alcohol, a copoly- and those which are boiling- Pure polymers of these substances mer of vinyl acetate and ethylene. water-sterilized, hot-filled, or are not melt-processable, so they pasteurized above 150°F. It may be modified by blending it are made into copolymer forms with another organic polymeric This material can be used on such as PVDC, EVOH, or AN. phase (polystyrene or nylon). refrigerated or frozen ready- prepared foods to reheated EVOH can be formed into films, be HP polyester in the container at the time of sheets, and rigid containers. It High-performance PET. This ma- provides excellent barrier to use, provided the specific film an terial has a melt point of 275°F has been tested and has been flavors and gases (such as carbon and can be melt-blown and hot- dioxide). has excellent shown not to release substances EVOH filled. The final container is yel- exceeding 0.15 milligrams per chemical barrier properties, so it low but has excellent barrier can be used with a wide variety of square inch of food-contact properties. For instance, it retains surface at 212°F. foods. There are three types of carbon dioxide in soda. EVOH: FSL 1. An ethylene content of 55 Hydrogen peroxide percent to percent vinyl Food-simulating liquids. These 30 An oxidizing agent used for cold are substances which are used to alcohol can be used with acid sterilization of packaging such as simulate the possible reactions aqueous and nonacid aqueous films and bottles before filling between food and materials with foods with no free surface oil; them with hot or sterilized food. dairy oil in which they come into contact. water emulsions; Residual hydrogen peroxide is oil-free beverages; The chemical characteristics of bakery prod- limited by the FDA to 0.1 parts FSLs are specific, so a particular ucts and dry solids with no free per million (ppm) after packaging food may be simulated with sev- surface oil; and foods that are (FDA 21CFR 178.1005). Hydro- in- hot-filled or pasteurized at eral food-simulating liquids gen peroxide is permitted as a 150°F or less, cluding distilled water, 3 percent and room-temper- sterilant for PET, olefins, and acetic acids (acid foods), 8 percent ature-, refrigerator-, or frozen- EVA. stored. or 50 percent ethanol (alcohol- containing foods), and n-heptane

(fat- or oil-containing foods). LDPE PE PET

Low-density polyethylene (see Polyethylene. Polyethylene is Polyethylene terephthalate, a PE). Maximum continuous ser- cleared for food contact surfaces polyester resin used for high-im- vice temperature is 140°F; it heat- as an "olefin polymer." The struc- pact resistant containers. When distorts at 104°F. LDPE is resistant ture of this polymer is relatively melt-blown, it provides a good to moisture vapor, acids, bases, loose, so it is a less effective bar- barrier for both flavors and hydro- and fats and oils. It has poor re- rier than PVDC or PVC. It was carbons (fat). It is not transparent. sistance to solvent and builds up introduced in the food industry in PET is resistant to acids, bases, static. LDPE is used primarily for the 1950s. PE can be produced by some solvents, and oils and fats. packaging films and for bread- two processes: low pressure pro- It is difficult to mold. PET is used wrapping bags. duces high-density PE, while high for soda, mouthwash, pourable

pressure produces low-density dressings, edible oils, and peanut OPP PE. Low-density PE is strong and butter. Monolayer films will hold Oriented polypropylene. OPP has clear. It is a good moisture barrier a crease, and are heat-sealable and good light and oxygen barrier but a poor oxygen barrier, and it transparent. The film is used for characteristics and protects against will heat-seal to itself. PE builds cereal box liners, soda bottles, boil- static and tends to cling to it- moisture. It is clear but will ac- up in-the-bag pouches, and micro- cept printing ink. OPP can be self. Its heat-sealing range is from wave food trays. The melting manufactured to be semirigid to 250 to 350°F. In general PE is point of unmodified PET is below cleared for use for packaging but flexible. It can be overlaid with boiling. At boiling temperatures, metalized polyester (silver, gold, not for cooking. Copolymers have bottles will shrink 30 percent and been tested and approved for use or colored). It is used for con- deform badly. Modified PETs trolled atmosphere snack foods in with aqueous acid and nonacid have melt points of 253 to 275°F. free oil that are which air has been flushed out foods containing These containers are more expen- and replaced with nitrogen to pre- heat-sterilized at temperatures sive, but they can be used for hot- over if the material is less vent development of rancid fla- 212°F filled products such as juice-based vor. Examples of these snack than 0.02-inch thick, or hot-filled beverages and tomato sauce. Heat food are chips in "bubble packs" or pasteurized at 150°F if the ma- distortion occurs at 180°F; maxi- 0.004- 0.02- and airline peanuts. terial is between and mum continuous service tempera- inch thick. PE has been cleared ture is 212°F. High-melting PET PC for irradiation sterilization up to is used for rigid trays of the type a total of 6.0 megarads. Certain used for TV dinners or entree Polycarbonate. PC is a rigid plastic. polymers have restricted uses, es- items. It can be heated in a micro- It is very clear and break-resistant. pecially with respect to tempera- wave or in a conventional oven at It is stable to acids and fats but has ture. 350°F for 30 minutes. There has poor resistance to bases and solvents. been a moderate amount of con- It will not tolerate continuous boil- cern that additives from these ing in water. Maximum continuous trays may migrate into foods, par- service temperature and heat distor- ticularly if the trays are reused in tion occur at 275°F. This material is a microwave oven. used for baby bottles. Recent legisla- tion in New York allows refill (up to

100 times) of polycarbonate plastic bottles for school milk programs and half-gallon milk containers for retail use. Plasticizers PP acid or nonacid foods and bever-

Substances used to increase the Polypropylene. Polypropylene ages containing no fat or oils. PS foams are used for hot beverage flexibility of polymeric (plastic) was introduced in the 1950s. It is films. They prevent formation of very transparent but cracks and cups, egg cartons, meat trays, and some of the bonds between poly- breaks at low temperatures (15°F). preparation cups for instant foods such as noodles and soups. mer molecules and make the It was used successfully in the films less rigid. Common plasti- mid-1960s as a copolymer with cizers include dioctyl adipate PE but was eventually replaced PVC

(DOA), which is used with PVC; by plain PE for bags. It is more Polyvinyl chloride. It is manufac- butylated hydroxyanisol (BHA), rigid, stronger, and lighter than tured by polymerizing vinyl chlo- which is used with polystyrene PE. It is resistant to water vapor, ride monomer. Plasticizers must and styrene; low-density polyeth- grease, acids, bases, and solvents, be added to give it flexibility. ylene (LDPE); high-density poly- and some polypropylenes are re- The structure of this polymer is ethylene (HDPE); and high-mo- sistant to high temperature. Heat relatively tight, but some air will lecular- weight hindered phenols, distortion occurs at 113°F; maxi- pass through it. PVC has a heat- which are used with ethylene- mum continuous service tempera- distortion temperature of 165°F vinyl acetate (EVA). Other ap- ture is 100°F. PP is cleared for and a maximum continuous ser- proved plasticizers are listed in irradiation sterilization up to 1 vice temperature of 150°F. Be-

The Food Chemical News Guide megarad total. Polypropylene is cause its shrink and melt points

(pp. 328.1-328.4). used for yogurt containers, marga- are so low, PVC can be used to rine tubs, and bottles for some shrink wrap foods which tolerate

Polyamide pourable foods such as syrup. very little heat. It is resistant to (Nylon-6, Nylon-12) water, acid, bases, some solvents,

A flexible packaging material PS fats, and oils. PVC is approved made from amino acids or dimer- Polystyrene, a rigid or flexible for use as the film to wrap fresh red it allows ized vegetable oils. Polyamides packaging material. PS is brittle. meats because enough air to pass through the are good oxygen and water barri- It heat distorts at 170°F. It is resis- ers, but they have low melting tant to water, oxygen (but not car- package to make the meat pig- points. Polyamides are approved bon dioxide), weak acids, bases, ments "bloom" bright red. PVC is Prior Sanctioned for use in gen- for use as food contact coating on and fats and oils, but it is dam- materials not to exceed room tem- aged by solvents and alcohol. PS eral food contact applications. peratures, as a component of paper- films are approved for irradiation The heat-sealing range is from 200 to 350°F. is approved for board, as sealing gaskets for food sterilization up to a total of 1 PVC containers, and as film coatings. megarad. PS can be formed into a irradiation sterilization up to 1 megarad. Certain polyamides are approved foam that is less brittle than solid for higher temperature applica- PS film. PS can be foamed using tions. Nylon-66 has a very high n-pentane, isopentane, or toluene melting point but is difficult to as the "blowing agent"; the use of heat-seal. Heat distortion occurs chlorfluorocarbons (CFCs) has at 400°F; maximum continuous been discontinued in the manu- service temperature is 175°F. facture of items used by the food

service industry. PS foam is approved for food use with aqueous 10

PVDC Susceptor

Polyvinylidene chloride, a co- A thin metalized film joined to a For more information contact the polymer of vinylidene chloride container (often paperboard) with Society of the Plastics Industry, 1275 Street N.W., Suite and vinyl chloride or methyl ac- an adhesive. Its purpose is to K 400, Washington, D.C. rylate. PVDC was invented in "heat up" in the microwave oven 20005; 1941 to protect equipment from to cause browning or crisping of (202)371-5200. outdoor elements. After World microwaveable foods such as

War II, it was approved for food pizza or to help generate enough packaging, and it was Prior Sanc- heat to cause popcorn to pop. tioned in 1956 (Society of the Susceptors attain temperatures of

Plastics Industry). PVDC is 450 to 500°F and have the poten- cleared for use as a base polymer tial for volatilizing the adhesives in surfaces of materials that con- and plasticizers in the packaging tact food, including food package material, causing them to migrate gaskets, coverings that come in into the food product. First- direct contact with dry foods, and generation susceptors used paperboard coating in contact aluminum-coated polyester film with fatty and aqueous foods. or paperboard. Second-generation The copolymerization results in a susceptors are currently being de- film with molecules bound so veloped; they will use nickel, co- tightly together that very little gas balt, iron, and stainless steel to or water can get through. The improve the susceptor's heating heat distortion temperature of the capacities. polymer is 113°F, and the maximum continuous service tempera- VCM ture is 160°F. PVDC films soften Vinyl chloride monomer. PVC at 250°F, so they can be used with can have residues of vinyl chlo- that is boiling, neces- food but not ride monomer (VCM) in the fin- sarily with high-sugar or high-fat ished plastic film. These levels foods that may get much hotter have been reduced to insignifi- than 212°F. PVDC and PVC can cant amounts since the late 1970s. be copolymerized to produce a The Codex Committee on Food family of flexible "Sarans." Additives and Contaminants has Sarans are clear and have excel- proposed guideline levels of lent barrier properties. Their lppm for VCM in PVC packages heat-sealing range is from 280 to and 0.01 ppm for the monomer in 400°F. PVDC is resistant to oxy- food. gen, water, acids, bases, and solvents.