Edible Films and Coatings: Tomorrow's Packagings: A Review

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Edible Films and Coatings: Tomorrow's Packagings: AReviewFrédéric Debeaufort a , Jesùs-Alberto Quezada-Gallo a & Andrée Voilley aa ENS.BANA - Université de Bourgogne, Laboratoire de Génie des Procédés Alimentaires etBiotechnologiques, 1, Esplanade Erasme, F-21000 DIJON, France; Tel: (+33) 03 80 39 68 43;Fax: (+33) 03 80 39 66 11. e-mail: [email protected]

Version of record first published: 03 Jun 2010

To cite this article: Frédéric Debeaufort, Jesùs-Alberto Quezada-Gallo & Andrée Voilley (1998): Edible Films and Coatings:Tomorrow's Packagings: A Review, Critical Reviews in Food Science and Nutrition, 38:4, 299-313

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Critical Reviews in Food Science, 38(4):299–313 (1998)

I. INTRODUCTION

The quality of food product depends onorganoleptic, nutritional, and hygienic charac-teristics, but these evolve during storage andcommercialization. Such changes are mainlydue to exchanges between foods and surround-ing media, or migrations between the differ-ent components in a composite food.

Many physical and chemical processes,such as sterilization, high pressure, radiationsor actives agents, were developed to steadyfoods and thus to preserve food quality. How-ever, the use of a performing package is neces-sary in the ultimate step of the preservationprocess. Therefore, packaging is preponder-ent for the durability of food quality.

The performance of synthetic packagingmaterials is appraised by their efficiency toreduce mass transfers between food and stor-age medium, that is, by the determination oftheir permeabilities. The constant progress insynthetic packagings, such as resins, cellulos-ic and plastic films, permitted the use of com-posite (copolymer) and/or multilayered filmpackagings, which are able to significantly re-duce gas and solute transfers selectively.

However, the suitability of plastic filmsis not universal. The combination of syntheticand edible packagings was proposed to increase

the efficiency of food quality preservation bythe packaging.1 In other respects, edible pack-agings are nonpollutant products because theyconsist of natural and biodegradable substanc-es from agriculture. Thus, they contribute tothe protection of the environment.

Over 90 patents and scientific papers con-cerning the manufacture of edible packaginghave been published since 1990. Most of thiswork deals with water vapor transfers, butsome other potential applications exist. Indeed,edible packagings can be used to encapsu-late aroma compounds,2,3,4 antioxydants, an-timicrobial agents,5 pigments, ions that stopbrowning reactions6 or nutritional substancessuch as vitamins.7

The characteristics required for ediblefilms and coatings depend mainly on the adul-teration of the food product, which may becoated. Therefore, low oxygen permeabilityis required for oxydation-sensitive productslike polyunsaturated fats. The properties ofmass transfer selectivity wished for are, forexample, to allow fruit and vegetable respi-ration (O2, CO2, ethylene exchanges) evenwhile limiting their dehydration during stor-age,8 or avoiding the solute penetration dur-ing the osmotic dehydration of fruits9.

Besides the barrier efficiency, edible filmsand coatings have to be organoleptically and

Edible Films and Coatings:Tomorrow’s Packagings: A Review

Frédéric Debeaufort,* Jesùs-Alberto Quezada-Gallo, and Andrée VoilleyENS.BANA - Université de Bourgogne, Laboratoire de Génie des Procédés Alimentaires etBiotechnologiques, 1, Esplanade Erasme, F-21000 DIJON, France; Tel: (+33) 03 80 39 6843; Fax: (+33) 03 80 39 66 11. e-mail: [email protected]

Referee: Dr. Pavinee Chinachoti, Food Science Dept., University of Massachusetts, Amherst, MA 01003

* Author to whom correspondence should be addressed.

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functionally compatible with foods. Althoughedible packagings offer numerous potentiali-ties to improve the quality and the shelf life offoodstuffs, little industrial applications weredeveloped. Indeed, the formulation of thesepackagings remains empirical and uneasy, whichmakes their use and application to foods rel-atively tricky. More fundamental research isthen necessary to better understand the trans-fer mechanisms of solutes and volatiles throughpolymeric polymers from agricultural origins,such as edible films and coatings.

II. HISTORY OF EDIBLE COATINGS

The use of edible films in food productsseems new, but food products were first cov-ered by edible films and coatings many yearsago. Wax has been used to delay dehydrationof citrus fruits in China since the twelfth andthirteenth centuries.10 While not the earliestuse of edible coatings, application of coatingto meats to prevent shrinkage has been the usualpractice since at least the sixteenth century,where meat cuts were coated with fats.11 Laterin the last century, the preservation of meatand other foodstuffs by coating them with gel-atin films was suggested.12 Yuba, a proteicedible film obtained from the skin of boiledsoy milk, was traditionally used in Asia toimprove the appearance and preservation ofsome foods since the fifteenth century.13 In the19th century, sucrose was initially applied asan edible protective coating on nuts, almonds,and hazelnuts to prevent oxydation and ran-cidness during storage. The more importantapplication of edible films and coatings untilnow, and particularly since the 1930s, con-cerns the use of an emulsion made of waxesand oil in water that was spread on fruits toimprove their appearance, such as their shini-ness, color, softening, onset of mealiness, car-riage of fungicides, and to better control theirripening and to retard the water loss. A num-ber of edible polysaccharide coatings, includ-

ing alginates, carrageenans, cellulose ethers,pectin, and starch derivatives, have been usedto improve stored meat quality.12 Over thelast 40 years, a great number of works on theformulation, application, and characterizationof edible films and coatings have been done inboth scientific and patent literature.

III. REQUIREMENTS FOR THE USEOF EDIBLE PACKAGINGS

When a packaging like a film, a sheet, a thinlayer or a coating is an integral part of a foodand is eated with, then it is qualified as “ed-ible packaging”.

Coatings are either applied to or made di-rectly on foods when films are independentstructures that can wrap food after their mak-ing. They are located on the food surface oras thin layers between several parts withinthe product, for example, between the fruitsand the dough in a pie.

Are edible packagings considered food in-gredients or should we be more cautious andqualify them as food additives? Nowadays,there is no regulation in the European Com-munity to specify how edible packagings haveto be classified.

Foods are described in the Codex Ali-mentarius as: all raw, partially treated or treat-ed substances used for human nutrition andfeeding. This concerns drinks, chewing gumand all components used in the formulation,preparation, making or treatment of foods, butturns down substances used as drugs, cosmet-ics and tobacco. If we consider the latter def-inition, edible films and coatings could beclassified as foods. However, in most cases,edible packagings do not provide a significa-tive nutritional value to the coated food, and,thus, they should be considered more like anadditive than an ingredient. It all depends onthe application of the edible packaging. It canalso be used to improve the nutritional quali-

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ty of the food, and thus be qualified as a foodingredient.

As food components, edible films and coat-ings usually have to be as tasteless as pos-sible in order not to be detected during theconsumption of the edible-packaged food prod-uct.12 When edible films and coatings have asignificant or particular taste and flavor, theirsensorial characteristics have to be compat-ible with those of the food.14

Although many functions of edible pack-agings are identical to those of plastic films,particularly their barrier properties to gas,vapors, and solutes, their use strictly requiresan overpackaging, notably for handling andhygienic reasons. Edible films appear to bea complementary parameter, interesting, andsometimes essential for the quality and sta-bility of some fresh, treated, or frozen foodproducts.12,15,16

Because they are both a packaging and afood component, edible films and coatingshave to fullfill some requirements:

• Good sensory qualities• High barrier and mechanical efficiencies• Enough biochemical, physico-chemical and

microbial stability• Free of toxics and safe for health• Simple technology• Nonpolluting• Low cost of raw materials and process17,18

IV. FUNCTIONALITY ANDCOMPOSITION OF EDIBLE FILMSAND COATINGS

Edible packagings must have some func-tional and specific properties. Indeed, first ofall they have to be selective toward mass trans-fers, but in some cases they have active prop-erties, or they can be both selective and active.

Selective properties of edible films andcoatings are summarized in Figure 1. In mostcases, the water barrier efficiency of films is

desirable to retard the surface dehydration offresh (meat, fruits, and vegetables) or frozenproducts. The water absorption inducing thecaking in food powder or the loss of crispnessin dried cakes, for example, could be delayedby coatings. The control of gas exchanges,particularly of oxygen, allows better controlof the ripening of fruits or to significantly re-duce the oxidation of oxygen-sensitive foodsand the rancidity of polyunsaturated fats, forexample. Organic vapor transfers have to bediminished in the aim to retain aroma com-pounds in the product during storage or to pre-vent solvent penetration in foods, which caninvolve toxicity or off-flavors. The penetra-tion of oil during frying and of sucrose orsodium chloride during osmotic dehydrationcan be limited by an edible film. One of themore interesting applications of edible filmsand coatings is their use inside a compositefood to control mass transfers between thedifferent compartments of the product, forexample in order to reduce water migrationin a pie. The effect of light and the effect ofUV light that involves radicalair reactions infoods could be reduced.

In the latter case, the efficiency of the filmto prevent light effect can be improved by theaddition of pigments or light absorbers. Thus,when films are carriers or used for encapsula-tion of food additives or ingredients, they areactive (Table 1). Edible packagings can im-prove mechanical properties of food to facili-tate handling and carriage. Sensorial character-istics such as colour, shininess, transparency,roughness or sticking can be improved. Ediblefilms and coatings enable to protect or sepa-rate small pieces or food portion for individ-ual consumption, or to isolate predosed quan-tities of food additives or ingredients in theaim of facilitating the formulation and the prep-aration of food in industrial plants.

Functional efficiency strongly depends onthe nature of components and film composi-tion and structure. The choice of film-form-ing substance and/or active additive is a func-tion of the objective, of the nature of the food

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FIG

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E 1

.S

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product and of the application method. So, lip-ids or hydrophobic substances such as resins,waxes or some non soluble proteins are themost efficient for the moisture transfer retar-dation.19 On the contrary, water soluble hy-drocolloids, like polysaccharides and proteins,are low efficient barrier against water trans-fer; however, their permeability to permanentgases is often lower than those of plastic films.Moreover, hydrocolloids usually provide high-er mechanical properties to edible packagingsthan lipids and hydrophobic substances. There-fore, the advantages of all substances can beused in composite films made from both hy-drocolloids and lipids. Natural film-formingsubstances, particularly proteins, need the useof film additives such as plasticizers to im-prove film resistance and elasticity or such asemulsifiers to increase the hydrophobic glob-ule distribution in composite emulsion-basededible films.20

Different types of edible packagings canbe obtained as a function of the composition

and the manufacturing technique. Indeed, ho-mogeneous films with a smooth surface areobtained from homogeneous solutions of poly-saccharides or proteins, or from molten lip-ids. Their appearance depends on the natureof the main component; for example, water-soluble cellulose derivatives give transparentand shiny films when gluten or casein-basedfilms are colored and unpolished. Some mix-tures of proteins and polysaccharides makehomogeneous edible packagings if all com-ponents are completely soluble in water or ina hydroalcoholic solution. Composite packag-ings are defined as films or coatings that struc-ture is heterogeneous, that is, composed witha continuous matrix with some inclusions, suchas lipidic globules in the case of an emulsion,or solid particules in the case of nonsolublesubstances (fibers, hydrophobic proteins), orcomposed of several layers. Usually, multi-layered films have better mechanical and bar-rier efficiencies than emulsion-based films andcoatings, but their manufacturing requires onestep of spreading or lamination and drying foreach layer. Therefore, their use in an indus-trial plan does not seem very interesting be-cause of too many steps in their making; onthe contrary, emulsion-based edible films pro-viding nearly the same properties, only re-quires one operation in their preparation.

V. FILM MANUFACTURINGPROCESSES

The formulation of films and coatings needthe use of at least one component capable toform a structural matrix with a sufficient co-hesiveness. Edible films made with severalsubstances have been perfected in order to ac-count for the complementary functional prop-erties of each component and to minimize theirdisadvantages. Most of the composite filmsstudied associate a hydrophobic compound,often lipids, and usually a hydrocolloid struc-tural matrix.10

TABLE 1Active Properties of Edible Filmsand Coatings

Encapsulation or carriageFlavors, spicesAntimicrobial, antioxydant agentsPigments, light absorbersSaltsOther food additives

Improvement of mechanical resistance

Improvement of appearanceColorShininessTransparencyRoughnessSticking

Individual protection of small pieces of food

Separation of food by individual portion

Soluble package for predosed food ingredients oradditives

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The film-forming substances are able toform a continuous structure by settling the inter-actions between molecules under the actionof a chemical or a physical treatment. Thefilm and coating formation involves one ofthe following processes:12, 15, 19

• Melting and solidification of solid fats, wax-es and resins,

• Simple coacervation where a hydrocolloiddispersed in aqueous solution is precipitedor gelified by the removal of the solvent,by the addition of a non-electrolyte solutein which the polymer is not soluble, by theaddition of an electrolyte substance induc-ing a “salting out” effect, or by the modifi-cation of the pH of the solution,

• Complex coacervation, where two hydro-colloid solutions with opposite charges arecombined, inducing interactions and theprecipitation of the polymer mixture,

• Thermal gelation or coagulation by the heat-ing of the macromolecule solution whichinvolves denaturation, gelification, precipi-tation, or by a rapid cooling of the hydro-colloid solution that induces a sol-gel tran-sition, for example.

Films, that is, independent structures, havebeen obtained in laboratories after laying orspreading a film-forming solution on support,drying it, and then detaching it. For industri-al processes, techniques used for the makingof flexible plastic films are transposable to edi-ble and biodegradable films.21,22 These tech-niques can be extrusion or coextrusion formultilayer films, lamination, and mainly roll-drying for the solvent removal of the polymersolution. Non-water-soluble film-forming sub-stances such as oils, fats and waxes are ap-plied on supports, on foods as emulsions ormicroemulsions in water, or as solutions inorganic solvents.10

Edible packagings are maily used as coat-ings in industrial process, and the techniquesused are traditional coating methods, such asspray fluidization, falling and pan coatings,

spraying, dipping, or brushing. These process-es are usually followed by drying steps foraqueous products, or by cooling for lipid-based coatings.19

The adhesiveness of the coating on thefood product surface mainly depends on itsrespective nature, that is, on its affinity, butlittle on the application or coating techniqueused. Adhesiveness depends on the nature andon the number of interactions or bondings be-tween film and support. So, the use of tensio-active substances such as emulsifiers makespossible the sticking of a hydrophobic coat-ing on very hydrophilic food products.19 Onthe contrary, the film thickness depends essen-tially on the application technique and on thesolution viscosity. Indeed, highly viscous so-lution cannot be or very uneasily sprayed, andthus only falling coating or dipping techniquesapply, giving high thickness to the coating.22

VI. EVALUATION OF EDIBLEPACKAGING PERFORMANCES

The suitable use of edible packagings strong-ly depends on their mechanical and barrierproperties. Therefore, the importance of accu-rate methodologies for determining film per-formances have been developed, particular-ly for the measurement of permeability valuesthat can be used in product shelf-life predic-tions. The apparatus used for permeability mea-surements are only standardized and availablefor water vapor and permanent gas transfers.They were introduced for plastic and synthet-ic packagings films.

Water vapor permeability (WVP) is de-fined as the rate of water vapor transmissionper unit area of flat material of unit thicknessinduced and per unit vapor pressure differencebetween two specific surfaces, under specifiedtemperature and humidity conditions. WVPmust not be mixed up with transport throughpores because it consists of a process of so-lution and diffusion where the solute vapordissolves on one side of the membrane, dif-fuses through to the other side, and then de-

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sorbes by evaporation.23 Several techniqueshave been perfected, based on infrared sensorssuch as the Permatran-W series available fromMocon (Modern Controls Inc., Minneapolis,MN, U.S.A.) or the WVP tester L80-4000 se-ries of Dr. Lissy (Lissy, Zurich, Switzerland),based on a coulometric method or a spectro-photometric methods as developed by Hollandand Santangelo.24 These techniques are wellfitted for high barrier efficiency polymers suchas plastics or wax-based edible films, but notfor hydrophilic polymers.1,25 The Permatran-W apparatus was only used by Gennadiosand Weller26 to determine the WVP of wheatprotein-based edible films. The most com-mon method used by people working onedible packagings is the “cup method” basedon the gravimetric technique.27,28,29,30 This isthe standardized method for the determinationof WVP through films and thin sheets of pack-agings.31,32,33 Modified “cup methods” weresuggested by several authors to prevent somedisadvantages such as the effects of stagnantlayers, or to control more accurately the va-por pressure and temperature gradients.34, 35

Gennadios et al.36 suggested a corrective calcu-lation taking into account the effect of stagnantlayers. A continuous weighing system with anelectric fan to maintain a large flow rate withinthe chamber was optimized by Debeaufort etal.37 ; it enables to follow the permeabilitykinetics and to minimize unstirred layers. Afurther advantage of the continuous measure-ment system was its significantly lower ex-perimental variability.15

The permanent gas permeability of edi-ble films was often studied for fruits and veg-etables applications, particularly oxygen andcarbon dioxide. Manometric and volumetricmethods described by the ASTM D143438 andISO 255639 standards were not used for edi-ble films. The apparatus generally used for thedetermination of the oxygen permeability offilms is based on coulometric sensor as theOxtran (Mocon, Modern Controls Inc., Minne-apolis, MN, U.S.A), or on manometric meth-ods, such as the Lyssy L100 series (Lyssy,

Zurich, Switzerland) for dry and noncorro-sive permanent gases, certified by the ASTMD3935 standard.40 However, these apparatusand techniques do not allow the measurementof gas permeability for different relative hu-midities as required when simulating the foodproducts. Even so, Oxtran was the more suit-able apparatus available for gas permeabilitydetermination through edible films.41,42 There-fore, some works on gas permeability of edi-ble packagings were carried out a gas chro-matographic method as developed by Karelet al.43 for plastic packagings, by Liebermannet al.44 for collagen films, by Hagenmaier andShaw45, 46 for lipids, waxes, and resins-basededible films. Recently, Debeaufort and Voilley3

have optimized a gas chromatographic meth-od to measure permanent gases, water, andorganic vapors transfers automatically, con-tinuously, and simultaneously .

Apart from the system developed byDebeaufort and Voilley,3 only one apparatusis available to measure organic vapors trans-fers through edible or plastic packagings de-veloped by Mocon. It is the same for solutepermeability such as salts, pigments, or lipids,although standardized methods exist for lipidmigrations in packagings,47,48 but there is noavailable systems. Therefore, Nelson andFennema49 were the first researchers who de-veloped a lipid permeability cell to study thefat transfers through water-soluble cellulosederivative films. The method for the salt andacid permeability determinations was improvedfor potassium sorbate and sorbic acid byVojdani and Torres50 and by Rico-Peña andTorres.5

An edible film or coating with very goodbarrier properties could be inefficient if itsmechanical properties do not permit to main-tain the film integrity during handling, pack-aging and carrying processes. Thus, the me-chanical resistance and deformability of ediblecoatings have to be determined. Traditionalmethods used for plastic packagings51, 52, 53,

are perfectly suitable and used for edible films.An apparatus such as a texturometer, a univer-

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sal tensile testing machine (Instron Engin.Corp., Canton, MA, U.S.A) or a dynamical-mechanical thermal analyzer, was often usedfor the tensile strength, elongation, deformabil-ity, elastic modulus, etc., characterizations ofedible films.13,35,54,55,56,57,58 The tensile testingmachine lets you study the effect of factorsas temperature or relative humidity on me-chanical properties.42,59,60,61

Several other film characteristics are of-ten studied, especially for the understandingof mechanical and barrier properties of films.These are the thickness, water sorption iso-therms, solubility in aqueous solutions or insolvents, diffusivity of solutes within thefilms, color and opacity, etc.

VII. APPLICATIONS OF “EDIBLEPACKAGINGS”

The choice of an edible packaging mainlydepends on the specific characteristics of thefood product that requires protection and onstorage conditions. Many materials have beenused for film and coating formulations suchas carbohydrates, proteins, lipids, or mixturesof these. Edible films and coatings have beenapplied on meat, poultry, seafood, fruits, veg-etables, grains, candies, heterogeneous andcomplex foods, or fresh, cured, freezed, andprocessed foods. The applications cited inthe following part only give examples of allpotentialities of edible films and coatings inthe function of the nature of the food productand of the polymer-film-forming agents.

A. Poultry, Meat, Fish, and Seafood

Carbohydrates, edible films, and coatingshave been often used to improve the qualityand the stability of meat during storage andcommercialization. Although carraghenan coat-ings have poor water barrier properties such

as most polysaccharides, they were applied onfresh and frozen meat, poultry and fish to pre-vent superficial dehydration.62 Indeed, the lossof product water is delayed until the water con-tained within the gel has been evaporated. Thelamb carcasses coated with alginates gelledwith calcium chloride are not preserved fromwater loss, but this method permits the reduc-tion of microbial growth.63 Moreover, the cook-ing loss, flavor, odor, and overall organolep-tic characteristics were not modified. The colorof beef loin pieces, off-odors, and appearanceare significantly improved after 96 h in algi-nate coatings.64 Stuchell and Krochta65 dis-played an efficient protection of salmon againstlipid oxidation and water loss by a coatingcomposed of a mixture of whey proteins andacetylated monoglycerides. Dinitrosyl ferro-haemochrome encapsulated in β-cyclodextrinsand further trapped in an edible coating layout on a nitrite-free meat cured product con-fers the color characteristics of a nitrite curedmeat after processing.66 The texture and juici-ness of beef steaks, pork chops, and skinnedchicken drumsticks were better when coatedwith a mixture of alginates and starch.67 Col-lagen, caseins, and cellulose derivatives suchas carboxymethylcellulose, methylcellulose,hydroxypropylmethyl-cellulose can be usedas a precoating to improve the adhesion ofthe batter mix onto meat and fish and signifi-cantly reduce oil absorption during frying.68,69

Water-soluble cellulose derivatives can alsobe used to make glazed sauces in order to min-imize runoff and water loss during cooking.The mixture of hydrocolloids (alginates, gums,cellulose derivatives, etc.) and acids (lactic oracetic acids) or antimicrobial agents laid outon meat pieces reduces the growth of microor-ganisms such as Listeria monocytogenes.70,71

Guts traditionaly used to provide shape andpreservation of sausages during fermentation,drying, or smoking are already mainly substi-tuted by collagenic and/or cellulosic edible films.The latter are more easily industrialized andallow a better control of the manufacturingprocess and storage.

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B. Fruits, Nuts, Grains,and Vegetables

The principal methods of fruit and vege-table spoilage are gas exchanges (respirationand transpiration) during ripening and storage,and/or microbial growth, particularly moldsand rots.72 Waxes (mineral oils, paraffin, car-nauba, candellilla, beeswax, polyethylene, shel-lac) are used largely as coatings on fruits suchas orange, lemon, grapefruit, apple, pear, cherry,banana, guava, mango, lychee, date, coco-nut, peach, grape, melon, and on some veg-etables such as carrot, cucumber, root crop,pumpkin, sweet corn, eggplant, pepper, toma-to, asparagus, celery, radish, potato, and tur-nip.16 Waxes and oils, alone or in emulsionwith hydrocolloid or protein solutions, arereally efficient barriers to water and can pre-vent from weight loss. However, a thicker lay-er of waxes strongly modify oxygene and car-bon dioxyde exchanges; this involves anaerobicstorage conditions inducing nonhomogene-ous ripening up to adulteration of fruits andvegetables.21 Consequently, some edible filmswere developed to better control the ripeningby reducing oxygen penetration in the fruit andincreasing CO2 and ethylene evaporation. Inaddition, proteins and polysaccharides, wheth-er mixed with lipids or not, present the bestratio between CO2 and O2 permeabilities, from10 to 25 when those of plastic wrappings arelower than 5.73 Indeed, corn zein coatings ap-plied on tomatoes or sucrose polyester “semper-fresh” applied on apples delayed color, weight,and firmness changes.56,57 Spoilage can be re-tarded or prevented by incorporating antimi-crobial agents within the film or by the natu-ral antifongic property of the hydrocolloid used.In such a manner, chitosan coatings inducethe production of the chitinase enzyme by thefruit itself, which is a natural antifongic agent.Chitosan coatings also have very selective bar-rier properties to gases and water vapor, thusallowing a good respiration and low water lossvia transpiration when they are layed out onthe strawberries or raspberries.8 Nuts, almonds,

hazelnuts, and peanuts are well protected againstoil migration and oxydation by low methoxypectin or cellulose derivative coatings. Pro-cessed fruits and vegetables can also be pre-served by coating during and after the manufac-turing processes. Mazza and Qi6 have shownthat the nonenzymatic browning of peeled andblanched potatoes can be inhibited by a coat-ing composed of gums, starch, gelatin, andcalcium chloride. A large number of fruits(grapes, apricots, bananas, guavas, mangoes,pineapples, etc.) are preserved during storageby air drying or osmotic dehydration. Be-cause of their high sugar content, they tendto be sticky and agglomerate. The loss of mois-ture causes the product to become hard andtough when water uptake involves spoilageand sometimes rancidness. Thus, some coat-ings made from wax, cellulose derivatives,starch, pectins, and/or proteins were suggest-ed to hinder these defects.74,75,76 To reduce sol-ute absorption, and particularly sucrose dur-ing osmotic dehydration, several authors haveshown that alginates, pectins, starch, or milkproteins are suitable barriers against soluteswhen they are applied on apples or papayaslices, for example.9,77,78

C. Confectioneries

Many candies require an edible coating toprevent stickiness, agglomeration, moistureabsorption, and oil migrations in the case ofchocolate or fat containing confectioneries.72

Indeed, milk and whey proteins, cellulose de-rivatives and edible varnishes like shellac orwax, are well known to reduce water and oilmigrations, like the oily or greasy feeling onfingers. These are used to make the M&M’s®

products commercialized by the Mars Com-pany. Similarly, dragees are the oldest ediblecoated confectioneries where the sugar coat-ing reduces the lipid oxidation of almond or nutcontained in the candy. Nelson and Fennema49

showed that methylcellulose films and coat-

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ings have a very low lipid permeability (lowerthan plastics) able to reduce fat migrationsand thus to inhibit the whitening or the bloom-ing of chocolate in confectioneries contain-ing other lipids than cocoa butter. Mixtures ofzein-ethanol used as film-forming solutionsobtain a better effect than the traditional con-fectioner’s glaze, with reduced drying time.26

Dyhr and Sorensen79 suggested the use of sor-bitol-based hard coatings to replace traditionalsugar coatings on chewable dragees. Bilayerfilms composed of a hydrocolloid film-form-ing agent and a wax layer that improved adhe-siveness was applied on chewing gum sheetsto extend shelf life and reduce moisture loss.This formulation was developed and patentedby the JR Wrighley Company.80 A new activefunction of edible films and coatings on sugar-based confectioneries and cereals was launched.It dealt with a coating that changes color whenimmersed in aqueous media like milk or themooth.81

D. Elaborated and HeterogenousFoods

The most interesting application of edi-ble films and coatings comes with elaboratesand heterogeneous foods. Indeed, plastic filmsor wrappings cannot be inserted within thefood product, for example, between the toma-to paste and the pastry or between the fruitmixture or the puree and the cake. A mixtureof stearic-palmitic acids and hydroxypropyl-methyl cellulose laid on the pastry is reallysuitable to reduce moisture transfers withoutmodifying the organoleptic properties of thefood product.28 The coating by dipping lightlydehydrated apricots into acetylated monoglyc-erides retains their water during cooking andstorage when they are incorporated in cakes.82

Several formulations were patented to reducemoisture transfers between low water activi-ty components (cereals, biscuits, dry nuts, orfruits) that have to be incorporated in highmoisture content compartments such as soup,

yoghurt, cream, puree, etc.83,84 A bilayer meth-ylcellulose and palmitic acid coating was test-ed as a moisture-impermeable barrier in sun-dae ice cream cones.85 This kept crispness inthe cone over 3 months. Nowadays, many ap-plications of edible films and coatings to het-erogeneous foods are applied, developed, ortested by industrial firms, but little data areavailable in the scientific and patent literature.

E. Noncoating Applications

Noncoating applications correspond to theuse of edible film-forming properties of foodsubstances such as protein or polysaccharidehydrocolloids in the making of films, casings,bags, and wrappings. Actually, only one in-dustrial edible bag is approved by the Frenchfood regulatory administrations (DGCCRF–AFNOR) and commercially available fromGemef Industrie S.A. This edible bag containsbreadmaking additives; it is named SOLUPAN,and consists of hydroxypropyl-methyl cellu-lose, starch, and potassium sorbate. Althoughfew edible bags, wrappings, and packagingsare available for purchase, many patents wereregistered; they describe the composition, mak-ing, and potential uses of edible films and pack-agings. Major components of edible films arehydrocolloids such as hydroxypropylmethylcellulose and glycerol (Monosol LPX 1832,Chris Craft Industrial Products, South Holland,Illinois, U.S.A.), starch and proteins,86 starchand softenings, firming, anticaking and col-oring agents,87 high amylose acetate starch,88

starch and gelatin,89 gelatin and collagen,90

collagen,91 chitosans,92 carrageenans and poly-hydric alcohol,93,94 curdlan, pectins, gums,and proteins95 soybean proteins,96 caseins andcaseinates,97 or fish proteins.98 Edible filmsusually have lower mechanical properties thanplastics, and, for hygienic reasons, they needto be overpackaged with traditional paper orplastic packagings. All the hydrocolloids usedin the edible film making are fully or partial-ly soluble in water. Thus, in most cases, their

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use is restricted to dry, low water activity, lowmoisture content, or powdered ingredients, ad-ditives, or food products. However, they haverelatively good processability and they are heatsealable and perfectly biodegradable.

VIII. BIOPACKAGING:THE FUTURE?

Edible coatings are very promising sys-tems for the future improvement of food qual-ity and preservation during processes and stor-age. Indeed, they could be used where plasticpackaging cannot be applied, that is, they canseparate several compartments within a food.Edible packagings are intelligent packagingsbecause they are both active and selective andhave infinite potential use. Edible films andcoatings are natural polymers obtained fromagricultural productions such as animal andvegetable proteins, gums, and lipids and areperfectly biodegradable, and therefore per-fectly safe for the environment. Their cost is10- to 50-fold higher than those of polyethy-lene or polypropylene films, but is the sameorder than complex, multilayered, or activeplastic films. However, their cost is not a hand-icap to their development because quantitiesused are very low, and they are especially ap-plied for very specific goals in value-addedfood products. Thus, the knowledge of ediblepolymers and that of plastic materials shouldbe used synergistically for the developmentof new applications, new biodegradable mate-rials, and new environmental approaches. Con-sequently, both plastic and edible packagingspotentiality appear to be a succesful key fortomorow’s food packagings.

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Edible Films and Coatings: Tomorrow's Packagings: A Review

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