potential of biobased materials for food...

Potential ofbiobased materialsfor food packaging

Karina Petersen,*Per Vñggemose Nielsen,*

Grete Bertelsen,y

Mark Lawther,{ Mette B. Olsen,x

Nils H. Nilssonk andGrith Mortenseny,{

*Department of Biotechnology, Technical Universityof Denmark, DK-2800 Lyngby, Denmark.

yDepartment of Dairy and Food Science, The RoyalVeterinary and Agricultural University, DK-1958Frederiksberg C, Denmark (fax: +45-35283245;

e-mail: [email protected]).{Department of Agricultural Sciences, The RoyalVeterinary and Agricultural University, DK-2630

Taastrup, Denmark.xDanishTechnological Institute,Centre forPackaging

and Transport, DK-2630 Taastrup, Denmark.kDanish Technological Institute, Centre for Product

Development, DK-8000 Aarhus C, Denmark.

During the last decade, joint e�orts by the packaging andthe food industries have reduced the amount of foodpackaging materials. Nonetheless, used packaging materialsare still very visible to the consumer in the context of dis-posal. Environmental issues are becoming increasinglyimportant to the European consumer. Consequently, con-sumer pressure may trigger the use of biobased packagingmaterials as an alternative to materials produced from non-renewable resources. Biologically based packaging isde®ned as packaging containing raw materials originatingfrom agricultural sources, i. e. produced from renewable,

biological raw materials such as starch and bioderivedmonomers. These materials are not necessarily biodegrad-able. Consequently, this review is not limited to biodegrad-able packaging. To date, biodegradable packaging hascommanded great attention, and numerous projects areunder way in this ®eld. One important reason for thisattention is the marketing of environmentally friendlypackaging materials. Furthermore, use of biodegradablepackaging materials has the greatest potential in countrieswhere land®ll is the main waste management tool. Biobasedpackaging materials include both edible ®lms and ediblecoatings along with primary and secondary packagingmaterials. Excellent in-depth reviews on edible ®lms andcoatings are already available [1±3]. Therefore, this reviewfocuses on biobased primary packaging materials for foods.Several concerns must be addressed prior to commercialuse of biobased primary food packaging materials. Theseconcerns include degradation rates under various condi-tions, changes in mechanical properties during storage,potential for microbial growth, and release of harmfulcompounds into the packaged food product. Furthermore,the biopackaging must function as food packaging andmeet the requirements of the individual food product. Thisreview evaluates the suitability of biobased packaging forfoods. Additionally, it identi®es the challenges involvedwhen using biobased packaging for di�erent foods. # 1999Elsevier Science Ltd. All rights reserved.

Rules and regulationsIn Europe, the biopackaging ®eld is regulated pri-

marily by two EU directives: ``Plastic Materials andArticles Intended to Come into Contact with Food-stu�s'' (90/128/EEC) [4] with later amendments, and``Packaging and Packaging Waste Directive'' (94/62/EEC)[5]. Table 1 outlines the main contents of these directives.Biopackaging often has di�culties complying with the

migration requirements of the directive on ``PlasticMaterials and Articles Intended to Come into Contactwith Foodstu�s''. Furthermore, several of the rawmaterials and additives used to produce biopackagingmaterials are not included in the list of approvedcomponents.

BiodegradationDegradation of a polymer may result from the action

of microbes, macroorganisms, photo-degradation or

0924-2244/99/$ - see front matter Copyright # 1999 Elsevier Science Ltd. All rights reserved.PI I : S0924-2244 (99 )00019-9

Trends in Food Science & Technology 10 (1999) 52±68

{Corresponding author. Present address: MDFoods, DK-8260 VibyJ, Denmark (fax: +45-8614 5029; e-mail: [email protected]).

Review

chemical degradation. In this review, only degradationcaused by microorganisms will be described in detail.Microbiological degradation may follow two routes:anaerobic degradation, which results in the productionof biogas (methane and hydrogen) that may be used asan energy source; or aerobic degradation, which yieldscompost or sludge.The overall approach to biodegradation tests is the

exposure of the test packaging material to an environ-ment containing an inoculate of microorganisms foundin the real degradation environment (sewage, soil, etc.).The sample is maintained in such a controlled environ-ment allowing the measurement of decreases in materialproperties and increases in metabolic products; carbondioxide if the test is aerobic, and methane production, ifanaerobic tests are performed. An important criterion inthis respect is the degree of biodegradation during acertain time frame.To date, several di�erent tests have been used, such as

the Closed Bottle Biological Oxygen (BOD) Test (NEN6634), Modi®ed Sturm Test (OECD 301B), OECDScreening Test (OECD 301E), Semi-Closed Bottle Test,Soil Burial Test [6]. The ASTM (American Society ofTesting and Materials) has developed several standardsfor photo- bio-, and chemically-degradable plastics tominimize confusion. These standards have no collectiveuniversal appeal, but several of them are quite popularand already exist in modi®ed forms in many countries.The Modi®ed Sturm Test produces the background forASTM D5209, which provides a test method for mea-suring the fraction of polymers converted to carbondioxide in an aerobic, aqueous medium containingmicrobes [7].Two sets of guidelines are used when evaluating

degradation: standards and practices. A standard testmethod provides a quantitative measure of biodegrad-ability with respect to the test conditions, whereas apractice outlines a procedure to generate a referenceenvironment, such as land®ll, compost, soil or theaquatic environment without providing quantitativeinformation. The future European CEN standards in

compliance with 94/62/EEC will most likely assess theproperties a packaging material must have in order todegrade. These include (1) biodegradability, (2) disin-tegration during biological treatment, (3) e�ect on thebiological treatment process, and (4) e�ect of the qualityof the resulting compost. The actual testing may bebased on existing standards.The authors anticipate that these standards will be

combined as this is the only operational development ina global market where the market share of biobasedpackaging of foods will increase dramatically in thecoming decades.

Optimal food packaging conditionsThe main purpose of food packaging is to protect the

product from the surroundings. Another purpose is tomaintain the quality of the food throughout the pro-duct's shelf-life. Furthermore, packaging must addresscommunication, legal, and commercial demands.Product shelf-life is controlled by three factors: pro-

duct characteristics, properties, and storage and dis-tribution conditions of the individual package [8].

Product characteristicsWhen selecting biobased packaging materials, it is

very important to know the characteristics of theapplicable food product. Deteriorative reactions infoods include enzymatic, chemical, physical, and micro-biological changes. Additional problems include insects,pests, and rodents.In a packaging context enzymatic changes in foods

are determined by temperature, water activity, andalteration of substrate (e.g. oxygen availability in oxy-gen-dependent reactions catalysed by enzymes).Deteriorative chemical changes in foods include

nonenzymatic browning, lipid hydrolysis, lipid oxida-tion, protein denaturation, protein crosslinking, hydro-lysis of proteins and oligo- and polysaccharides,polysaccharide synthesis, degradation of natural pig-ments and glycolytic changes [9]. These reactions oftentake place simultaneously in foods and their reactantsand products interrelate. Furthermore, enzymatic, phy-sical, and microbiological factors also interact, makingfoods very complex matrices to work with. However,such complexity is intriguing to the scientists! The ratesof these chemical reactions depend on numerous para-meters, which may be controlled by proper choice ofpackaging. These include light (intensity and speci®cwavelengths), partial pressures of gases (e.g. oxygen andcarbon dioxide), water activity, and temperature.The physical properties of foods can be de®ned as

those properties lending themselves to description andquanti®cation by physical rather than chemical means[10]. Physical changes include softening, toughening,loss of solubility, loss of water holding capacity, wet-ting, lumpiness, caking/agglomeration, emulsion

Table 1. EU legislation on packaging [4, 5]

Plastic materials and articles intended to come into contactwith foodstu�s (90/128/EEC)� Lists allowed monomers, additives, etc. to be used in

the production of packaging materials for foods.� Outlines both total migration limits as well as speci®c

migration requirements for numerous compounds.� Sets standards for the production and use of packaging

materials and the labelling of these materials.

Packaging and Packaging Waste Directive (94/62/EEC)� Regulates the production of packaging materials� Regulates waste management and the use of recycling,

composting, and energy recovery by incineration.

K. Petersen et al. / Trends in Food Science & Technology 10 (1999) 52±68 53

instability, swelling/shrinkage, and crushing/breakage.In a packaging context, control of moisture sorption(barrier properties) is of utmost importance as a meansof preventing physical changes. Furthermore, selectionof packaging materials and methods as well as distribu-tion and storage conditions a�ect the rates and type ofphysical deterioration.A wide range of bacteria and fungi (yeasts and

moulds) is represented in foods. A speci®c group oforganisms is associated with each type of food (micro-biota). The microbiota and its development over time isdetermined by a number of factors; e.g. initial microbialload, pH of the product, water activity (aw), redoxpotential (Eh), nutrients (e.g. minerals, sugars, and vita-mins), antimicrobial compounds, physical structure ofthe product, storage temperature, relative humidity, andconcentration of gases in head space (particularly oxy-gen and carbon dioxide).Most importantly, the package functions as a protec-

tion from contamination or attack by microorganisms.Thus, the mechanical properties must match the actualstorage conditions and the product characteristics.Additionally, water activity, antimicrobial compounds(released from the packaging material), relative humid-ity, and concentration of gases in head space can bein¯uenced by proper package design. Some packagingmaterials may be a source of contamination of the foodproduct. Scholte (1995) [11] showed that counts of 100colony forming units per 100 cm2 may be expectedespecially when recycled paper materials are used.Plastics usually show lower counts but may attract dustdue to build-up of static electricity. Many ®lamentousfungi might be expected to withstand the extremeenvironmental conditions biological packaging materi-als are subjected to during manufacture and can growand reproduce in packaging materials. Narciso andParish (1997) [12] showed that several fungi could growon carton material utilizing it as a nutrient source.However, studies on polyethylene ®lm containing cornstarch did not show better survival of bacteria com-pared with polyethylene ®lm [13]. Enhanced growthcould only be detected in low nutrient food (e.g. bottledwater packaged in corn starch containing ®lms),whereas no di�erence was detected for more nutritiousfoods.

Properties of the individual packageKnowledge of both product characteristics and sto-

rage and distribution conditions dictates the requiredbarrier properties of the packaging materials used for aspeci®c application. Barrier properties include perme-ability of gases (O2, CO2, N2, ethylene, etc.), watervapour, aromas, and light. These are vital factors formaintaining the quality of foods. However, packagingmaterials cannot be chosen solely on the basis of theirbarrier properties. Factors such as processability,

mechanical properties (tensile strength, elongation, tearstrength, puncture resistance, friction, burst strength,etc.), migration/absorption (overall and speci®c), andchemical resistance must also be taken into account.The fact that the packaged food actually interacts withthe packaging material makes the scenario even morecomplicated, as this may change the initial mechanicaland barrier properties of the packaging materials.

Storage and distribution conditionsEnvironmental factors, such as temperature, relative

humidity, and light intensity, to which the product isexposed during storage and distribution, must also betaken into consideration when selecting packagingmaterials. Transportation damage may happen to theproduct. The extent of such damage can be reduced byproper packaging and by adjusting the distribution pat-tern according to the transported product. Table 2summarizes typical storage conditions and factorsdetermining shelf-life for various foods. Additionally,the table lists the optimal barrier properties and gascomposition within the package.

Animal derived productsFresh meatsFresh meats demand high oxygen levels on the pro-

duct surface to ensure the red oxymyoglobin colour.This may be obtained by packaging the product ineither a ®lm with high oxygen permeability or by Mod-i®ed Atmosphere Packaging (MAP) containing highlevels of oxygen. The permeable ®lm results in a limitedproduct shelf-life as Gram negative bacteria will developrather quickly. This is even more pronounced when themeats are ground as the surface area increases dramati-cally; thus, only a one-day shelf-life may be expected.MAP with high oxygen (70±80%) often in combinationwith high levels of carbon dioxide (20±30%) inhibits thetraditional microbial growth on the surface of freshmeats, but allows slow growth of lactic acid bacteria,especially Carnobacteria spp. Beef has the highest con-centration of myoglobin and is the darkest meat species,while pork, which has the lowest concentration, has thelightest colour. pH and morphology of the muscle alsoimpact on meat colour [14]. Preserving the red oxy-myoglobin colour by optimal choice of packaging(including gas composition) in beef is of utmost impor-tance, while it is less crucial in the lighter colouredmeats, i.e. pork and poultry. This should enable theproducers to use higher CO2 levels to obtain longershelf-life. However, some authors point out that morethan 25% CO2 may cause discoloration and o�-¯avourformation in poultry [15, 16]. Also the ``snug-down''e�ect obtained at high CO2 levels, when a large portionof the CO2 is dissolved in the water phase, is undesirablefor several products as it gives the package a vacuumpackaged look.

54 K. Petersen et al. / Trends in Food Science & Technology 10 (1999) 52±68

Table 2. Optimal requirements of packaging materials for di�erent foods a [10]

Food Typical time/temp. Quality factors determining shelf-life Required gas composition Optimal required barrier properties

Microbiology Colour Oxidation Structure Flavour Others O2 CO2 H2O Light Other

Animal derived productsRed meats 0±5�C 6±14d X X ± ± ± ± High oxygen

(70±80%), highcarbon dioxide

(30±20%)

High High (High) ± ±

0±5�C 1±4d X X ± ± ± ± No control:atmospheric

Low ± (High) ± ±

Other meats 0±5�C 1 d±6w X (x) ± ± ± ± Low oxygen,high carbondioxide

High High (High) ± ±

Cured meat productsCured ®sh products

5�C 4w5�C 4w

XX

XX

XX

±±

±±

±±

No oxygen,high carbondioxide

HighHigh

HighHigh

(High)(High)

HighHigh

±±

Fish, high fat 0±5�C 1±7d X ± X ± X Enzymatic carbon dioxide (40%),Oxygen (30%)

and nitrogen (30%)

High High Low ± Odours

Fish, low fat 0±5�C 1±7d X ± ± ± X Enzymatic Carbon dioxide(40±60%) and

nitrogen (60±40%)

High High Low ± Odours

Eggs 2±12�C 25 d±4w X ± ± ± ± Water loss ± ± ± ± ± AromaFluid milk 2±5�C 2 d±8 md X ± X ± X Photooxidation ± High ± High High Aroma

±Fermented milk 2±5�C 16±18 d X ± X X ± Photooxidation ± High High High High Aroma

±Fresh cheese <5�C 1±8 w X ± ± ± X Photooxidation ± High High High High ±Semi soft and hard cheese <5�C 1 w±18w X ± X ± ± Photooxidation ± High Low High Low or

high±

Mould ripened cheese <5�C 1±8 w X ± ± ± X Photooxidation ± High High High High ±Butter, oil, dairy spreads, etc. <5�C 6 w or more X ± X ± X Chemical, enzymatic ± High ± High (High) Odours

greasePastas (fresh) 2±5�C 4 w X ± (x) ± ± ± Low oxygen High High (High) (High) ±Fruits and vegetablesRoot crops 0±25�C from 1w X ± X X ± ± No oxygen,

no carbon dioxideHigh High High High Odours

Most vegetables 0±25�C from 1w X ± X X ± ± Oxygen (1±5%),no carbon dioxide

High High High High Odours

Most fruits andsome vegetables

0±18�C from 1w X ± X X ± ± Oxygen (1±5%),carbon dioxide (0±5%)

High High High High Odours

Dry productsFlour/grains 2�C-room temp. 3 yr. X ± X ± ± Enzymatic ± ± ± High ± ±Powders, high fat Room temp. 1 yr. ± ± X ± X Staling Low oxygen High ± High High ±Powders, low fat Room temp. > 1 yr. ± ± ± ± X Stale ¯avour Low oxygen High ± High (High) ±Breakfast cereals Room temp. 1 yr. ± ± X ± X Humidity Atmospheric/low

oxygenHigh Low High ± ±

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Table 2 (continued)

Food Typical time/temp. Quality factors determining shelf-life Required gas composition Optimal required barrier properties

Microbiology Colour Oxidation Structure Flavour Others O2 CO2 H2O Light Other

Pastas (dried) Room temp. 1±6 md ± X X ± ± Enzymatic ± ± ± High ± ±Spices and herbs Room temp. from 6 md ± X X ± X ± ± (High) ± High (High) ±Snack foods Room temp. 1 yr ± X X ± X Enzymatic loss of

cripness, Hydrolytic rancidityLow oxygen High ± High High ±

Co�ees/teas 5�C-room temp. 1 yr ± ± X ± X Staling Low oxygen High Low High High ±Breads 5�C-room temp, 1d-12w X ± ± X ± Staling Low oxygen,

high carbon dioxideHigh High High ± ±

Cakes 5�C-room temp. 1d-4 md X X X X ± ± Atmospheric/lowoxygen, highcarbon dioxide

High High High (High) ±

Crackers andcookies

Room temp. 4 md ± X X X X Loss of crispness ± ± ± High ± ±

Chocolates 2�C-room temp. 6±12 md ± X X ± X ± ± ± ± ± High Odours,greese

BeveragesWater Room temp. 1 yr X ± ± ± X Migration, absorption ± ± ± High ± AromaJuice 5�C-room temp. 5d-1 yr X X X ± X

(Scalping)Photo oxidation Atmospheric, low oxygen High ± High High ±

Carbonated drinks(beer & soft drinks)

5�C-room temp. 6 md-1 yr X ± X ± X Absorption, migration High carbon dioxide,low oxygen

High High High High ±

Frozen foodsHigh fat products ÿ18�C 1 yr ± (x) X (x) ± ± Low oxygen High ± High (High) ±Low fat products ÿ18�C 2 yr ± (x) (x) (x) ± Enzymatic (Low oxygen) High ± High (High) ±OthersHigh fat products(dressing, sauce, etc.)

5�C-room temp. 1 yr ± (x) X ± ± ± Low oxygen High ± High High Aroma,grease

Ready meals 2±5�C 3±21d X ± X ± (x) ± Low oxygen, highcarbon dioxide

High High High ± ±

ad=Day(s), w=week(s), md=month(s), yr=year(s).

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Cured meat productsA cured meat product is de®ned as one to which

sodium chloride has been added and in which thepigment myoglobin is mainly in the nitroso-form, as aresult of reaction with nitric oxide (NO). In uncookedcured meat products, the attractive red colour is thatof nitrosylmyoglobin which has the red colour char-acteristics of fresh meat oxymyoglobin. Heatingdenatures globin and converts nitrosylmyoglobin tonitrosylhemochrome which has a characteristic red±pink colour.Most cured meat products are sold as sliced, retail-

packaged products. At the beginning of storage slicedcured meat products deteriorate because of discolora-tion. Later on during retail storage microbial changesand oxidative rancidity may occur in the products [10].The pigment of cured meats (nitrosylmyoglobin andnitrosylhemochrome) oxidize rapidly to metmyoglobinin the presence of light and oxygen. Thus, cured meatsmay fade within hours under display conditions [17].The rate of photooxidation of the pigment to metmyo-globin increases directly as the partial pressure of oxy-gen increases [18]. Vacuum packaging or MAP in ananoxic atmosphere reduces photooxidation of the pig-ment. However, residual oxygen must be very low.Storing vacuum packaged meats in the dark for fourdays before exposure to display light has resulted inreduced colour deterioration, due to depletion of resi-dual oxygen by microorganisms and tissue respirationactivities [19]. Other techniques such as active packaging(oxygen-absorbing sachets) have reduced photooxida-tion of cured meats [20].

Sea foodsMajor factors determining shelf-life in sea food

include autolysis caused by intrinsic enzymes, metabolicactivity of micro-organisms, and oxidation. Autolyticspoilage depends on factors such as temperature, pH,oxygen availability, and the physiological conditions ofthe ®sh before death. Thus, lowering of the oxygencontent in the package may reduce the rate of autolyticspoilage. Low oxygen containing packaging atmo-spheres inhibit growth of putrifying bacteria such asPseudomonas, Moraxella, Acinetobacter, Flavobacteria,and Cytophaga. However, anoxic conditions at tem-peratures above 3�C enable Clostridium botulinum topropagate [21, 22].The fat content in sea food ranges from less than 1%

(e.g. cod and haddock) to 30% (e.g. herring and mack-erel). The high-fat products are very prone to oxidation,as they are very high in polyunsaturated fat; this causesformation of rancid and oxidative o� ¯avours. As aresult the typical packaging atmosphere used for non-fatty ®sh consists of 30% O2, 40% CO2, and 30% N2.Modi®ed atmosphere packaging (MAP) of smoked/fatty ®sh products typically takes place in 40±60% CO2

and balanced with N2 [11, 21]. Excessively high CO2

levels may cause extensive drip [23].

Egg productsEgg products are distributed as both refrigerated,

frozen, and spray dried products. The shelf-life of shelleggs is determined primarily by storage temperature andhumidity, with refrigeration being the major controllingfactor. The major deterioration in a packaging contextis breakage of the egg shell which may be prevented byusing shock absorbing containers. Furthermore, bacteriamay penetrate the shell; thus, eggs should be kept cleanand condensation on the egg should be avoided. Acoating preventing carbon dioxide and moisture lossincreases shelf-life considerably [24].

Dairy productsMilk, cream, fermented milk products, and processed

cheese all require low oxygen permeability to avoidoxidation and microbial growth. Dairy products shouldbe protected against light-induced oxidation (whichcauses, for example discoloration, o�-¯avour forma-tion, and nutrient loss), and against water evaporation.Products such as yoghurt require protection againstphysical disruption (syneresis).Several researchers have recommended that fresh

cheeses (e.g. cream cheese, decorated cream cheese, softcheese, and cottage cheese) are packaged in modi®edatmospheres with N2 and/or CO2 replacing the O2 in thepackage [25±27]. However spoilage caused by yeast andespecially bacteria may still occur even at very low O2

and elevated CO2 levels [28]. Semisoft and hard cheeses(whole, sliced or shredded) have a relatively highrespiration rate, which require a packaging materialsomewhat permeable to CO2 to avoid blowing of thepackaging. Meanwhile, oxygen must be kept out toavoid fungal spoilage and oxidation of the cheese. Theprimary spoilage organism on these cheeses is Peni-cillium commune [29].Mould ripened cheeses, such as white cheeses (Brie/

Camembert) and blue-veined cheeses (Danablue andRoquefort), contain active fungal cultures. As a con-sequence, the oxygen content should not be too low asthis may cause anaerobic respiration and production ofo�-¯avours. Additionally, a change in atmosphericcomposition can cause a change in the microbiota.Instead these products require a balanced oxygen andcarbon dioxide atmosphere to prolong shelf-life [30, 31].

Fruits and vegetablesFruits and vegetables are living organisms which

continue to respire and transpire after harvesting. Fruitsand vegetables are characterized by a high respirationrate, i.e. oxygen is used, and carbon dioxide and otherproducts of the primary metabolism (e.g. ethylene) areproduced. Respiration and transpiration rates of fresh


fruits and vegetables are often good indicators of theirstorage life; the higher the rate, the shorter the shelf-life[32].Short-term preservation extends shelf-life by reducing

respiration and transpiration rates. This is done bycontrolling factors such as temperature, relative humid-ity, gas composition (ethylene (C2H2), O2 and CO2),light, mechanical/physical damage such as bruising,cutting, and puncturing and by applying food additivesand treatments such as sorting, waxing, and irradiation.Relative humidity (RH) may be controlled by proper

packaging. The optimal RH for most fruits is 85±95%and 90±98% for most vegetables (except dry onions andpumpkins). Some root vegetables demand almost 100%RH [28]. Moisture loss or uptake causes wilting,shrinkage, and loss of ®rmness, crispness, and succu-lence of the product. However, too high a moisturebarrier causes a high RH in the package, which is con-ducive to microbial growth [33]. Acidic fruit tissue isgenerally attacked and rotted by fungi, while vegetables,having a higher tissue pH and aw, are more susceptibleto bacterial decay.Reduction of the oxygen concentration to less than

10% provides a tool for controlling the respiration rate.In most cases, the packaging atmosphere must be con-trolled within a relatively narrow range, since exces-sively low oxygen levels result in anaerobic respirationand production of o�-¯avours and o�-odours. Addi-tionally, very low oxygen levels facilitate growth ofanaerobic bacteria like the toxigenic Clostridium botuli-num. However, if the oxygen level is insu�cientlyreduced, maturation and chemical and microbial dete-rioration will occur without delay. Ethylene productionis reduced by either low O2, high CO2, or both, and thee�ects are additive [34]. Elevated CO2 levels may inhibit,promote, or have no e�ect on ethylene production infruits [10]. Table 3 based on Floros (1990) [35] showsthe recommended controlled atmosphere/modi®edatmosphere conditions for fresh fruits and vegetableswhen kept at the conditions most frequently reported inthe literature.Packaging should retain desirable odours, in for

example strawberries, and prevent odour pickup (e.g. indried products [36]). Additionally, packaging may pro-vide protection from light. This is crucial for the shelf-life of products such as potatoes and Belgian endive.The packaging should give su�cient protection againstmechanical damage caused by transportation or handling(e.g. compression and vibration damage). Careful handlingand proper packaging may minimize physical damage,thereby also delaying microbial and enzymatic spoilage.

Dry productsDry products are characterized by long shelf-life

which is mostly due to the low water activity (aw) of theproducts. Thus, fungal and bacterial growth is seldom a

problem under normal storage conditions. The lowwater content dictates that the products should be keptunder dry conditions. A good moisture barrier is the keyto successful packaging of dry products. Water ingressresults in caking (e.g. in ¯our and instant co�ee), loss ofcrispness (e.g. in breakfast cereals and snack foods),starch recrystallization/retrogradation (e.g. in pasta),staling (in co�ee), and microbial growth. Furthermore,increased aw in the packaged product may accelerateoxidative reactions [37].Other factors determining shelf-life include:

. Breakage of the product (e.g. breakfast cereals,snack foods, and pastas). Thus, good compressionresistance is required.

. Oxidation of colour and aroma compounds, vita-mins, and the lipid fraction. The rate of these pro-cesses can be minimized by using non-translucentmaterials (e.g. for co�ee/tea, snack foods) and O2-depleted packaging atmospheres (e.g. for co�ee/tea and for high fat products like snack foods).

. Rodent and insect infestation. Infestation can beprevented by proper storage of the product fromproduction to end-consumer, and by the use of,for example, multi-layer packaging materialswhich are free of leaks.

. Evolution of CO2 in co�ee after roasting andgrinding. This can be solved either by degassing inopen holding tanks for 4±5 h prior to packaging,by using CO2-valves integrated in the package orby using CO2 absorbers in the package.

Bakery productsThe shelf-life of bread depends to a great extent on

hygienic conditions during production, the use of pre-

Table 3. Recommended controlled atmosphere/modi®ed atmosphereconditions for fresh fruits and vegetables (from Floros, 1990) [35]

Group Commodity CO2 (%)a O2 (%)a

1 Potatoes 0 0Carrots 0 0Beets 0 0

2 Tomatoes 0 3±5Peppers 0 3±5Cucumbers 0 3±5Lettuce 0 2±5Celery 0 2±4Onions (dry) 0 1±2

3 Pears 0±5 1±3Lemons 0±5 5Apples 1±5 2±3Cauli¯ower 2±5 2±5Artichokes 3±5 2±3Peaches 5 1±2

4 Others 5±15 1±5

aPercentages are volume or mole percentage; the remainder isnitrogen.


servatives and the headspace atmosphere used. Fungalgrowth, staling, and moisture absorption/desorption arethe main shelf-life and quality determining factors. In apackaging context fungal growth is prevented by usingmodi®ed atmospheres containing 70±100% CO2 and 0±30% N2 or by removing O2 by absorbers. Staling, i.e.retrogradation of starch, is primarily caused by moist-ure loss. This can be prevented by packaging the pro-duct in high H2O barrier materials. The e�ect of CO2 onprevention of staling is questionable [38].Crackers and cookies have a long shelf-life due to the

low aw (0.1±0.3) of the products [10, 38]. The majordeteriorative processes include loss of crispness due tomoisture absorption, oxidation of the fat fraction, fatbloom (development of a greyish colour), and breakage.The latter may be reduced signi®cantly by using packa-ging materials resistant to mechanical compression.Loss of crispness may be prevented by using a propermoisture barrier in the package. In a packaging contextoxidation of the fat fraction may be stalled using low O2

atmospheres and packaging materials with high O2

barrier properties. Non-translucent packaging materialsmay also hinder light-induced oxidation. Fat bloom isrelated to temperature ¯uctuations during storage andis, therefore, not a�ected directly by the packaging.In cakes, quality deterioration includes microbial

spoilage (fermentation or visual growth), crumb staling(dryness or development of o�-¯avours), rancidity (o�-¯avour development), crystallization of sugars (e.g.grittiness in cream ®llings), syneresis of jams and jellies,o�-¯avours and odours other than rancidity, chocolatebloom, structural weakness, colour fade, colour change,and transfer, and ®nally moisture migration and loss[10]. As in the case of bread, crackers, and cookies,intelligent choices of packaging parameters such asmoisture barrier, O2-depleted atmospheres, etc. for theparticular cake type may improve both product qualityand shelf-life.Chocolate is sold in varieties where chocolate is not

the only ingredient, (e.g. nuts and caramel may beadded). Product defects include fat bloom, sugar bloom,oxidative or lipolytic rancidity, and absorption of for-eign odours. Fat bloom is mostly caused by temperature¯uctuations and improper selection of raw materials.Sugar bloom may be a�ected by use of re®ned sugarwith a high moisture content or storage in high humid-ities. The latter may be controlled partly by the choiceof packaging (H2O barrier). Rancidity may be pre-vented by using packaging materials with su�cient bar-rier to light, O2, and H2O. Finally, absorption of foreignodours may be prevented using materials with higharoma barriers.

BeveragesFactors determining shelf-life include microbial chan-

ges, migration/scalping, oxidation of vitamins, aroma

compounds, and colourants (both natural and arti®cial).In carbonated products, CO2 loss is the main quality-determining parameter.In packaging of water, prevention of ¯avour sorption

is of utmost importance. Microbial growth is often hin-dered through processing methods, e.g. aseptic packagingand chemical treatment, making the product fairly stable.The shelf-life of juice varies with the heat treatment

given prior to/after packaging; thus microbial spoilagemay be caused by subsequent contamination by yeastsand moulds or by heat resistant yeasts and moulds.Other defects include non-enzymatic browning, oxida-tion of vitamins, colour, and ¯avour changes as well asscalping. Scalping (migration) of ¯avour componentssuch as d-limonene into the package has been thor-oughly researched [39, 40]. Scalping may be preventedusing packaging materials inert to the migrating ¯avourcomponents and with a low aroma permeability. Oxi-dation of the product and mould growth can be pre-vented by using materials with low O2-permeability andlow light transmission. The product pH is low. Thus,the package must be resistant to acids. In carbonatedbeverages, shelf-life is determined primarily by loss ofCO2, oxidation or hydrolysis of ¯avour components,and absorption/migration. CO2 loss is prevented byusing packaging materials with high barrier propertiestowards gases and moisture. Sizing the bottle also playsa role (surface area:product volume ratio). Further-more, the package should withstand high internal pres-sures produced by the CO2 [1±7 atm pressure(temperature dependent)] [10]. Low light transmissionhinders oxidation of colourants, which can be a pro-blem in soft drinks. Hop oxidation in beer, which causesobjectionable o�-¯avour formation, may be reducedusing non-translucent packaging. In beer, a low O2-permeability is also required. Oxygen scavenger bottleclosures may be used to prevent oxidative reactionsthereby ensuring product quality and shelf-life [41].Since beverage products are stored for extensive time

periods (�1 year), packaging demands great moisturebarriers in order to prevent packaging collapse andwater loss.

Frozen foodsThe deteriorative reactions taking place during sto-

rage of frozen foods are mainly chemical in nature,including degradation of pigments and vitamins, oxida-tion of lipids, and destabilization of proteins. Packagingplays a key role in protecting frozen foods from dete-rioration. Packaging procedures protecting the frozenfoods from oxygen and light have been proved to reducepigment and lipid oxidation in frozen prawns [42] andfrozen salmonoides [43]. Oxidation catalysed byenzymes that have not been eliminated by blanching(e.g. from vegetables) may occur if an e�ective O2 bar-rier is not utilized.


Moisture loss by sublimation from the surface of theproduct leads to freezer burns. Moisture loss impairsthe visual appearance of the product and leads to unac-ceptable product weight losses. Sublimation of waterfrom the frozen food is avoided by using a packagingmaterial which is highly impermeable to water vapourand sticks tightly to the surface of the frozen food [10].Physical damage to the packaged frozen foods may be

prevented by proper handling and by using e.g. rigidcontainers. Obviously, the packaging materials shouldbe able to withstand low storage temperatures. Addi-tionally, the materials should provide a grease barrierfor products with a high fat content.

OthersButter, fats, and oilsButter, fats, and oils are more susceptible to chemical

deterioration than to microbial spoilage. The maindeteriorative reactions include oxidative and hydrolyticrancidity; the latter caused by lipases naturally presentin the product or due to microorganisms. Due to thelow aw the growth of mould is favoured compared withbacterial growth. Oxidation may be prevented byexcluding light and residual O2 from the packaging.Hydrolytic rancidity may be prevented by proper heattreatment prior to packaging. The package must beresistant to grease and should provide a good watervapour transmission barrier to prevent dehydration ofe.g. butter. Products such as butter readily absorbodours and consequently should be packaged in mate-rials with an su�cient aroma barrier [44].

Ready-meals and fast food productsThe shelf-life determining parameters of chill-stored

ready-meals include oxidative changes and growth ofmicroorganisms. In cooked meat, oxidative changesoccur rapidly resulting in a characteristic o�-¯avourdenoted Warmed Over Flavour (WOF). WOF is causedby oxidation of the highly unsaturated phospholipidfraction of the cell membranes. In aerobic packagedready-meals WOF may be recognized within 24 h aftercooking. Ready-meals containing cooked meat must,therefore, be either vacuum packaged or packaged in ananoxic modi®ed atmosphere [45]. To inhibit growth ofspoilage microorganisms, 20±30% of carbon dioxide isrecommended in the applied modi®ed atmosphere. Alow storage temperature (<5�C) must be retainedduring the entire storage period to avoid growth ofpathogenic microorganisms, e.g. Salmonella andListeria.The markets for home meal replacements and ready

meals are expanding throughout the western world.Increasing demands for convenience without compro-mising quality have led to an almost explosive growth indemands for home meal replacements and ready meals.Biobased packaging is an obvious choice for packaging

of these products as they are high value products thatare consumed within a few days.

Biobased materialsThe future generation of packaging materials will be

derived from renewable resources. These materials willideally be biodegradable. However, natural polymericmaterials vary in their rate of degradation in the envir-onment, and some proteins, for example, cannot pre-sently be classi®ed as degradable because of standardde®nitions [46].Polymers derived from renewable resources (``biopo-

lymers'') are broadly classi®ed according to method ofproduction. This gives the following three main cate-gories:

1. Polymers directly extracted/removed from naturalmaterials (mainly plants). Examples are poly-saccharides such as starch and cellulose and pro-teins like casein and wheat gluten.

2. Polymers produced by ``classical'' chemical synth-esis from renewable bio-derived monomers. Agood example is polylactate, a biopolyester poly-merised from lactic acid monomers. The monomeritself is produced via fermentation of carbohydratefeedstock [47].

3. Polymers produced by microorganisms or geneti-cally transformed bacteria. The best known bio-polymer types are the Polyhydroxyalkanoates,mainly polyhydroxy-butyrates and copolymers ofhydroxy-butyrate (HB) and hydroxy-valerate(HV) [48]. Such copolymers are produced byMonsanto and are better known by the generictrade name ``Biopol2''. Polyhydroxyalkanoatesfunction in microorganisms as energy substratesand for carbon storage [49].

Materials from all three categories are either alreadyused for packaging or have considerable potential inthis area. However, the packaging ®eld is still domi-nated by mineral oil derived polymers such as poly-ethylene (PE) and polystyrene (PS), despite globalconcerns about the environment, indicating that pro-blems remain associated with the use of these renewablematerials. A notable exception is ``cellulose'', which inthe form of paper and cardboard/carton enjoys wideusage as an exterior packaging layer [50]. Unmodi®edcellulose in this form is very biodegradable. However,paper is ®brous and opaque with poor barrier andmoisture resistance properties. Hence, its role willremain limited to exterior packaging of foods except invery speci®c cases (e.g. dry products).The problems associated with renewable biopolymers

are threefold: performance, processing, and cost.Although these factors are somewhat interrelated, pro-blems due to ``performance and processing'' are more


pronounced with polymers extracted directly from bio-mass (e.g. cellulose, starch, proteins). Conversely, poly-mers belonging to categories 2 and 3 above, generallyperform very well and are easily processed into ®lmsusing standard plastics techniques, but tend to beexpensive compared with synthetic analogues [51]. Mostcommonly available natural polymers (category 1above) are extracted from agricultural or forest plantsand trees. Examples are cellulose, starch, pectins, andproteins. These are cell wall, plant storage (starch) orstructural polymers. All are by nature hydrophilic andsomewhat crystalline; all factors causing processing andperformance problems.Cellulose is a good example. It is the most abundant

natural polymer on earth and it is an essentially linearpolymer of anhydroglucose. It is a cheap raw materialcosting between 0.5 and 1 ECU per kg before derivati-zation. As a consequence of its chemical structure, it ishighly crystalline, ®brous, and insoluble [52]. Hence, for®lm production, cellulose is dissolved in an aggressive,toxic mixture of sodium hydroxide and carbon dis-ulphide (``Xanthation'') and then recast into sulphuricacid. This produces a cellophane ®lm. Cellophane hasgood mechanical properties. It is hydrophilic and, con-sequently, sensitive to moisture. Cellophane is not ther-moplastic and is, therefore, not heat-sealable. It is oftencoated, e.g. with nitrocellulose wax (NC-W) or poly-vinylidene chloride (PVDC), because of its relativelypoor moisture barrier properties. At low relativehumidity levels cellophane is a good gas barrier; how-ever, barrier properties are reduced at intermediate andhigh relative humidities. Coating reduces the in¯uenceof the relative humidity on the barrier properties [2], butinevitably increases production cost.Alternatively, cellulose may be derivatized from the

solvated state, via esteri®cation or etheri®cation ofindividual hydroxyl groups on the polysaccharidebackbone. A number of derivatives are commerciallyavailable, including cellulose acetate, ethyl cellulose,hydroxy-ethyl cellulose, and hydroxy-propyl cellulose.Cellulose modi®cation is, therefore, costly and di�cult;the least expensive derivative is the diacetate costingaround 3±4 ECU per kg [50]. For realistic thermoplasticprocessing, cellulose acetate needs addition of up to25% plasticizer. There may be considerable potential forthe use of a bio-derived plasticizer. However, at present,none is commercially utilized. The gas and moisture bar-rier properties of cellulose acetate are not optimal withrespect to food packaging. Some grades of celluloseacetate (degree of substitution less than 1.7) are biode-gradable, although at a slower rate than cellophane [2].Starch is another widely abundant polysaccharide

obtained in granular form from corn, cereal grain, rice,and potatoes. Starch is essentially a mixture of amylose,an almost linear polymer of anhydroglucose, and amy-lopectin, a highly branched polymer of anhydroglucose

(Fig. 1 and 2). The ratio of the two components variesaccording to starch types utilized. Starch enjoys wideusage in several non-food sectors, most notably in thesizing and coating of papers, as an adhesive, a thick-ener, and as a ``green strength'' additive to simple com-posite materials such as briquettes [53]. In the packaging®eld, starch recently has received great attention [54]. Itis very biodegradable and has inherently low cost (0.5±1.5 ECU per kg), but is also very hydrophilic (poormoisture barrier). Finally, it is partially crystalline.Films based on starch have moderate gas barrier prop-erties. Their mechanical properties are generally inferiorto synthetic polymer ®lms. When a plasticizer, such aswater, is added starches exhibit thermoplastic behaviour[2]. Because of these factors, starch requires substantialprocessing before a stable ®lm is produced. This is gen-erally achieved via ``destructuration'' and plasticizationin an extruder, or modi®cation. It is also commonpractice to add copious amounts of synthetic polymer tothe starch. This is normally polyvinyl alcohol (PVA) orpolycaprolactone. Films produced have reasonabletransparency. The starch component of the ®lm is trulybiodegradable; the other components degrade duringcomposting. This is signi®cantly di�erent to the oldertechnology in which starch was blended with PE toproduce a ®lm which disintegrates, the starch compo-nent biodegrades, leaving small particles of PE. Starch-PVA materials are, however, very sensitive to moisture.Furthermore, hydrophobation increases costs [55].An alternative strategy is direct chemical modi®cation

of the starch. Industry produces modi®ed starch for anumber of end uses already, but this normally repre-sents only surface modi®cation of starch granules (e.g.cationic starches for paper treatment) [56]. Few ``fully''modi®ed starches are on the market at present. Themodi®cation route is likely to be costly, although starchis less crystalline and more chemically accessible thancellulose. In addition, starch is more vulnerable todegradation during modi®cation than cellulose, andconditions employed need to be mild to prevent exten-sive depolymerization and loss of properties. Researchis needed in this area to utilize the full potential of star-ches. Despite all of the above factors, starch remains themost promising of the available polysaccharides forfood packaging, as it is easier to process than cellulose,is low cost, and very biodegradable. The challenge lyingahead is to develop strategies to improve the moisture

Fig. 1. Chemical structure of amylose.


stability of starch ®lms without eliminating thesefavourable factors.Proteins have commanded renewed attention as

degradable, renewable polymer ®lms. Traditionally,proteins are used in adhesives and as edible ®lms/coat-ings. However, they have considerable potential asslowly degrading packaging ®lms. Proteins are attrac-tive to the polymer chemist as they possess a wide rangeof chemical functionalities, and molecules with wideranges of properties are available in nature. Extrusionapplications are possible with respect to plant proteinssuch as wheat glutens and seed proteins. Animal pro-teins, such as casein, keratin and collagen, are alsoavailable. However, proteins derived from ``waste ani-mal tissue'' like collagen are unlikely to be attractivefrom the consumer standpoint because of recent adversepublicity deriving from the BSE crisis in the BritishIsles. Protein ®lms have demonstrated good gas barrierproperties and many are water resistant, though notentirely hydrophobic [1]. A barrier to the mass proces-sing of plant proteins as packaging ®lm is a lack of basicknowledge as to the tertiary and quaternary structures ofcomplex materials such as gluten. These data are neededfor full utilization of the materials in packaging. Poten-tial costs of protein ®lms range from 1±10 ECU per kg.By way of contrast, the Biopol2 type products [poly-

hydroxyalkanoates (PHA)] possess excellent ®lm-form-ing and coating properties. PHAs are produced withproperties close to PE, polypropylene (PP) or polyester

(PET). They are biodegradable on soil contact, waterresistant, and are readily processed in standard indus-trial plastic plants [57]. The present barrier to bulk use iscost. This is partially connected with the manufacturingroute (for example, isolation of the polymer from themicroorganisms is generally costly), and partly produc-tion scale. The properties of the ®lm may be adjusted bychanging the ratio between hydroxyvalerate (HV) andhydroxybutyrate (HB), which can be achieved bymanipulation of the growth media. A high content ofpolyhydroxybutyrate (PHB) gives a strong and sti�material, whereas polyhydroxyvalerate (PHV) improves¯exibility and toughness. The polyalkanoates are morehydrophobic than the polysaccharide-based materialsresulting in a material with good moisture barrierproperties, whereas the gas barriers are inferior. Thepolymer currently costs around 10±12 ECU per kg, ascompared with an originally projected kg cost of 3±5ECU [58]. If this projected cost is realised, the potentialof this polymer type in packaging is excellent. Figure 3illustrates the structure of PHA.A more immediate option is polylactates (PLAs) pro-

duced via classical polymerization of the renewable fer-mentation product, lactic acid. Polylactates alsoperform well compared with standard thermoplastics,and the production of ¯exible, water-resistant ®lm hasbeen demonstrated [59]. Again, the material is very bio-degradable under controlled conditions and can be pro-cessed using standard industrial machinery. Although

Fig. 2. Chemical structure of amylopectin.


not yet produced in bulk, larger scale production isbeing evaluated by at least two companies (Cargill DowPolymers and Neste). Prices of around 2±4 ECU per kgare forecast, and if prices of approximately 2 ECU perkg are achieved the packaging potential is very high,assuming adequate barrier properties can be met. Poly-lactates have good mechanical properties. The moisturebarrier is better than for the starch-based materials,whereas the gas barrier is inferior. The ®nal polymercost may well depend on the e�ciency of the initial fer-mentation process to produce the lactic acid monomeras the polymerization step is an adaptation of industrypractice for production of stepwise polymers. Figure 4shows the structure of PLA.The biopackaging material may contain further nat-

ural extracts/components, e.g. lignin and waxes whichact as preservatives stalling the initial spoilage processof the food product. This process still needs thoroughtesting. Furthermore, the use of natural antioxidants,plasticizers, etc. in the production of biobased packa-ging materials should be addressed.In general, bulk commodity thermoplastics commonly

used in food and drink packaging such as PE, PS, andPET are made in high volume at large productionplants, and as such are relatively inexpensive due toeconomy of scale and relatively low unit processingcosts. PE costs around 0.7±1 ECU per kg, whereas PScosts twice as much. Because of this quantity, con-tinuous production, product quality and performance isnow easy to monitor, and parameters such as moistureand gas barrier of ®lms are reproduced readily. Many ofthe natural polymer derivatives (cellulose esters andethers, starch derivatives, etc.) are still produced inbatch reactors and are hence more expensive and sub-ject to quality variations. Despite the relatively low cost

of the starting materials. A key factor in the spreadingof bio-derived polymers in food packaging is, therefore,the development of analogous continuous processes formanufacture of biopolymer ®lm at reduced cost and toa pre-de®ned quality. Another key factor in this is pro-duction of polymer resins that can readily be processedinto ®lm using existing industrial machinery, onlynecessitating minor modi®cation of the productionplant. In this respect, the polymers with the best pro-spects for commercial production are the polylactatesand the PHA's, provided initial fermentation or bio-production costs can be reduced. In addition, the starchbased systems which can be continuously extruded arepromising, provided factors such as moisture resistanceand moisture barrier can be improved.Table 4 depicts the most promising materials starch/

PVA, PHA and PLA for packaging compared to sometraditional polymers, low density polyethylene (LDPE)and PS. The reader must bear in mind that this table isbased on existing results and prices anticipated with fullscale production.

Biopackaging of foodsOne of the challenges facing the food packaging

industry in its e�orts to produce biobased primarypackaging is to match the durability of the packagingwith product shelf-life. The biologically based packa-ging material must remain stable without changes ofmechanical and/or barrier properties and must functionproperly during storage until disposal. Subsequently,the material should biodegrade e�ciently. Environ-mental conditions conducive to biodegration must beavoided during storage of the food product, whereasoptimized conditions for biodegration must exist afterdiscarding. The most important parameters for controlling

Fig. 3. Chemical structure of polyhydroxyalkanoate (PHA).

Fig. 4. Chemical structure of polylactate (PLA).


stability of the biologically based packaging materialare appropriate water activity, pH, nutrients, oxygen,storage time, and temperature. Thus, dry products maybe safely stored for extended periods, whereas moist foodswould have limited storage periods [2]. Prior to usingbiobased materials for primary food packaging, thee�ects on food quality and food safety must be examined.For many years, coated cellophane and cellulose

acetate have been utilized for food packaging. Coatedcellophane is used for e.g. baked goods, fresh produce,processed meat, cheese, and candy. Cellulose acetate isused mainly for baked goods and fresh produce [2]. Themoisture and gas barrier properties of cellulose acetateare not optimal for food packaging. However, the ®lmis excellent for high-moisture products as it allowsrespiration and reduces fogging [60].Recently, a biodegradable laminate of chitosan-cellu-

lose and polycaprolactone ®lm was developed in Japan.Makino and Hirata (1997) [61] examined the applic-ability of the laminate for modi®ed atmosphere packa-ging (MAP) of horticultural commodities. Thesuitability of the laminate for MAP of head lettuce, cutbroccoli, whole broccoli, tomatoes, and sweet corn wastested by computer simulation using respiration rateequations stated in the literature. The results encourageuse of the biodegradable laminate for the above men-tioned products within a 10±25�C temperature range.Scienti®c tests have been performed on starch-con-

taining materials for use in food packaging (Table 5).Holton et al. (1994) [62] evaluated the suitability of anordinary polyethylene (PE) ®lm and a PE ®lm contain-ing 6% corn starch when used for packaging of broc-coli, bread, and ground beef stored under normal timeand temperature conditions. The type of packaging ®lmseemingly did not a�ect the evaluated quality para-meters, i.e. bread staling, broccoli colour, and lipid oxi-dation of ground beef. However, a signi®cant loss ofelongation occurred in corn starch containing PE ®lmwhich could be due to interactions between the ®lm and

free radicals developed during lipid oxidation in groundbeef during frozen storage. Inconsistent results werefound when packaging broccoli and bread in cornstarch ®lm. Therefore, Holton et al. (1994) [62] recom-mended that corn starch based PE ®lm be used only forpackaging of wet and dry low-lipid foods. However,they discouraged use of the ®lm for high fat contentfoods due to possible interactions between the ®lm andfree radicals derived from lipid oxidation.Strantz and Zottola (1992) [13] and Kim and Pometto

III (1994) [63] evaluated the survival of bacteria on beefand bologna packaged in a corn starch containing PE®lm (Table 5). Starch addition (0±28%) did not impairheat-sealing, nor did it accelerate microbial growth inground beef. Additionally, colour stability during refri-gerated and frozen storage was not a�ected. Themechanical properties of the ®lms used for packaging ofground beef were not signi®cantly changed after refri-gerated or frozen storage [63]. Strantz and Zottola(1992) [13] inoculated lean beef and bologna with Sal-monella typhimurium, Bacillus cereus, and Staphylo-coccus aureus and found that bacterial growth andsurvival were not enhanced by the presence of cornstarch (6%). They also examined the migration of thesame bacteria by inoculating the exterior of the packa-ging material with bacteria and found no migration ofbacteria through either the PE ®lm or the corn starchcontaining PE ®lm. Both studies established that themicrobiological quality of the foods was not a�ected bythe presence of corn starch in PE ®lms; this leads to theconclusion that corn starch containing PE ®lms havetrue potential as primary food containers for selectedproducts.In Belgium, packaging containing starch is used com-

mercially for fast-food packaging of French fries. Otherapplications include disposable food service items andpaper coatings [2].The R&D activities within the polylactate and poly-

alkanoate ®elds have been intensi®ed during the last

Table 4. Comparative properties of bio-derived polymers and comparison with polyethylene and polystyrene (Adapted from [2] and [67], along with references[50±59])

Polymer Moisture permeability Oxygen permeability Mechanical properties Expected price (ECU/kg)a

Cellulose/cellophane High±medium(low if coated)

High Good 1.5±3

Cellulose acetate Moderate High Moderate(needs plasticiser)

3±5

Starch/Polyvinyl alcohol High Low Good 2±4Proteins High±medium Low Moderate 1±8Polyhydroxyalcanoates(Polyhydroxybutyrate/valerate)

Low Low Good Present: 10±12Projecteda: 3±5

Polylactate Moderate High±moderate Good Projecteda: 2±4Low density polyethylene Low High Moderate±good 0.7±2Polystyrene High High Poor±moderate 1±2

aProjected: at full scale production


decade, and packaging materials are now readily avail-able. In the case of both polylactate and polyalkanoatebased packaging, a lack of published scienti®c studies isvery evident. However, Danone, a dairy company, ispresently testing the use of polylactate based cups foryoghurt packaging. Other potential commercial appli-cations of polylactate based materials also include dis-posable food service items and bags (for example,bakery products). With respect to polyalkanoate, sug-gested use within the food sector includes beverage bot-tles, coated paperboard milk cartons, cups, fast foodpackaging, and ®lms [64].More recently, French researchers have demonstrated

that the use of gluten ®lms may actually be advanta-geous for storage of respiring fresh produce [65]. Thegluten-based ®lm had suitable O2 barriers whileremaining su�ciently permeable to carbon dioxide.Thus, a modi®ed atmosphere containing 2±3% O2 and2±3% CO2 was developed, which the authors claim isfavourable to the overall quality of mushrooms.

Future use of biopackaging for foodsIn the previous sections, the properties of biobased

materials have been described. The requirements to bemet for various food groups with regards to the packa-ging materials have also been described. When compar-ing these two descriptions with each other and with

Table 5, it is obvious that many food products areunsuited for biobased packaging as it exists. It is,therefore, important to identify foods suitable for thesepackaging materials. Furthermore, the manufacture ofbiobased packaging is considerably more expensive thanthe production of traditional packaging, i.e. poly-ethylene (PE), as the biobased materials are often pro-duced batch-wise in small-scale operations.Another important issue is public opinion. It is gen-

erally accepted that consumers should be more con-scious of the environment. Hence, it would beconsidered environmentally friendly to buy foods inbiopackaging based on renewable resources. Consumersare probably willing to pay more for an environmentallyfriendly product, and this has to be taken into accountwhen selecting the food products for biobased packa-ging. In addition, biobased packaging for foods mayprovide new possibilities for modi®ed atmospherepackaging (MAP). Biobased packaging may providenew atmosphere conditions, which improve the qualityof speci®c food products during shelf life (e.g. vege-tables).It appears that the barrier properties of biopackaging

materials, in particular the moisture barrier properties,are inferior to existing packaging materials. This is par-ticularly true when biobased packaging is used as pri-mary packaging. This problem can be solved in di�erent

Table 5. Application of biopolymers for food packaging

Food product Biopackaging Storage conditions Main results Reference

Fresh mushrooms Glass jar coveredwith gluten ®lm

10�C for 140 h(�6 days)

A modi®ed atmospherecontaining 2-3% CO2

and 2-3% O2 developedduring the storage period

Barron et al.(1997)cf. Guilbert et al.(1997)

Fresh products(shredded lettuce andcabbage, head lettuce,cut broccoli, wholebroccoli, tomatoes,sweet corn andblueberries)

Laminate of chitosan(14.5% by weight)-cellulose(48.3%) and polycaprolactone[glycerol (36.2%) and protein(1.0%)]

10±25�C for4±6 days

The biodegradablelaminate was foundsuitable as a packagingmaterial with MAP in theinert temp. range

Makino and Hirata(1997)

Lean beef and bolognainoculated withpathogenic bacteria

Polyethylene with corn starch(®nal conc. 6%)

4 and 21�C for3±13 days

Survival was not enhancedby the presence of cornstarch

Strantz and Zottola(1992)

Bread, broccoli, andground beef

Cornstarch-containing (CSC)poly-ethylene. Final cornstarchconcentration were 6% inthe ®lm

Temperaturesappropriate forrecommendedstorage periods

CSC ®lm was e�ective ascontrol ®lm in protectingstored food, but the ®lmshould not be used topackage foods in whichlipids would be in contactwith the ®lms surface understorage, because of lipidoxidation

Holton et al.(1994)

Ground beef Starch-polyethylene ®lmscontaining corn starch(0-28%), low- or high-molecularweight oxidized polyethyleneand pro-oxidant

ÿ18�C for 4 weeksor +10�C for 2 days

Starch-polyethylene ®lmshave potential use asprimary food containersfor ground beef

Kim and Pometto III(1994)


ways. The immediate solution is to package foods thatare compatible with the materials and their properties.However, it is also possible to use an edible coating withthe required barrier properties for the food and subse-quently use the biobased materials as primary packa-ging. The primary packaging material may be producedfrom monomaterials which are favoured in terms ofsource collection. This also minimizes the amount ofpackaging material used. Coating of the biobasedmaterial could also be an option; the coating could, forexample, be wax which would add hydrophobicity tothe packaging material. Technology also makes it pos-sible to laminate two biobased materials together ordesign a laminate with biobased materials mixed withsynthetic materials. Finally, a secondary packaging, notbiobased, may be used.It may be necessary to modify the biobased materials

to improve their properties with respect to food packa-ging. This will naturally increase the price of the endproduct, due to, for example expenses for research anddevelopment of the optimal modi®cation of the mate-rial. The price level of the packaging material alsodepends on the production scale. A lower price isanticipated in the case of large-scale production.Migration is another important factor in food packaging.

Before using biobased packaging material as a primarypackaging material for foods, migration (overall andspeci®c) must be researched in order to avoid harmfulsubstances migrating to the food product in contact withthe packaging. Active edible coatings or biobased mate-rials where migration of e.g. antioxidants and anti-microbial compounds is desired also must meet the legalrequirements, and this must again be tested thoroughly.Many biobased food packaging materials are biode-

gradable. Thus, the microbial stability of the materialduring storage until disposal must be tested before usingthe material as a primary packaging material for foods(legislation about relevant compounds is needed, com-pounds used in the production (additives and plastici-zers) must be approved).The authors do see possibilities in using biobased

packaging for food both in the immediate and remotefuture. There are still a few obstacles in the way beforethis can become a reality. The western consumersdemand high quality food products, and they areincreasingly aware of environmental issues. Consumers®nd not only the origin and treatment of the foodimportant, but also the disposal of the food packaging.If consumers ®nd the food satisfactory, they are willingto pay more. Indeed, recent consumer surveys show thatthe consumers are willing to pay more for food pack-aged in biobased materials which are more friendly tothe environment [66]. Therefore, biopackaging oforganic foods is a possibility, because they are typicallymore exclusive and expensive. Another food groupsuitable for biobased packaging is ``high value'' fruit

and vegetables, e.g. mushrooms and minimally pro-cessed salads with short-shelf life. We believe it isimportant that biobased materials have an image ofsomething which comes from agricultural sources andbiodegrades in nature, causing no harm to the envir-onment. In connection with this, life cycle analyses(LCA) must be carried out for biobased packagingmaterials.Legislation is another aspect that cannot be ignored.

It is of vital importance to identify a standard way oflabelling the material or package. This labelling shouldindicate that the packaging is based on renewableresources. This makes it easier for the consumers todi�erentiate between the various food products, and itfacilitates sorting of the waste. Many European coun-tries incinerate household waste. Systems could bedeveloped where disposal of packaging for incinerationis taxed, whereas no tax is imposed on compostablebiobased packaging made from renewable biodegrad-able resources. Additionally, standards must be madefor the new types of biobased packaging. Many of thecompounds used to manufacture the biobased packa-ging are not incorporated in the current legislation.The agricultural policy of the EU addresses the issue

of using surplus stocks in Europe (mainly wheat andcorn). In addition, a large amount of residual agri-cultural products has today no use, but could be a partof the production of e.g. polylactate (PLA).

ConclusionIn conclusion, this review indicates that research

e�orts to date primarily have focused on the productionand the mechanical properties of the biobased polymers.Little attention has been paid to the interactionsbetween the polymers and the food products. Fewinvestigations on food stability and quality when pack-aged in biobased materials have been published indi-cating that the science of biologically based packagingmaterials for foods is still very much in its infancy.There is now much research e�ort being expended

world-wide, both fundamental and applied. Therefore,it may be assumed that most of the present problemswill be solved within a reasonable time. Gradual appli-cation of legislative and consumer pressure is beginningto initiate real commercial interest in this area. This willinevitably continue and the rate of development willparallel this enhanced commercial awareness.Great possibilities exists for packaging in biobased

materials. The most obvious products are high priceproducts and niche products e.g. organic products.However, further research within di�erent areas of bio-packaging, e.g. legislation, processing technology, andcompatibility studies of foods and packaging must beinitiated before biobased materials can be used for pri-mary food packaging.


AcknowledgementsThis research was sponsored by the program,

``Increased Utilization of Renewable Resources forIndustrial Non-Food Purposes (1997±2001)'' under theauspices of the Danish Ministry of Food, Agricultureand Fisheries. A special thank to Gina Fischer,Department of Agricultural Sciences, The Royal Veter-inary and Agricultural University, DK-2630 Taastrup.

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