| Abstract | Original Articles Scalping of Flavors in Packaged Foods MG Sajilata 1 K Savitha 1 RS Singhal 1 and VR Kanetkar 1 1 Authors are with Food Engineering and Technology Dept Inst of Chemical Technology Univ of Mumbai Matunga Mumbai-400 019 India Direct inquiries to author Singhal (E-mail: rekha@udctorg) Introduction Food packaging in recent years has experienced rapid advances and continuous growth due to consumer desire and demand for conveniently packaged products This has promoted a trend in packaging materials that has evolved from simple food wraps to sophisticated containers Besides providing an adequate shelf life and product quality it is desirous that the packaging material also participates in the overall flavor management of the packaged food flavor being an underlying factor in the consumer acceptability of all food products However sorption of food aromas particularly by plastic packaging materials is usually perceived as a major factor contributing to the quality alteration of most foods during storage This causes changes in both the intensity and characteristics of the food flavors owing to their absorption by the packaging material a phenomenon commonly referred to as scalping (Roland and Hotchkiss 1991) Flavor scalping is a term used in the packaging industry to describe the loss of quality of a packaged item due to either its volatile flavors being absorbed by the package or the food absorbing undesirable flavors from the packaging material The inability to prevent scalping is a sore point for many packagers a classic example being the absorption of various plastic flavors when soft drinks are stored in plastic bottles for an extended period of time Tropicana discovered that its gable-topped orange juice cartons scalped flavor from the juice by absorbing important chemicals Polyethylene (PE) the most common plastic used in commercial products including beverages is a top scalper Commercial plastics for food packaging include simple homopolymers or copolymers such as low-density polyethylene (LDPE) medium-density polyethylene (MDPE) high-density polyethylene (HDPE) polypropylene (PP) polyethylene terephthalate (PET) aluminum sheet (Surlyn) ethylene vinyl alcohol copolymer (EVOH) and others (Gremli 1996) Figure 1 shows the molecular structures of the polymers used as packaging materials (Willige 2002) Among the plastic materials polyethylenes and polypropylenes (homo- and copolymers) are mostly used in package design preferred for contact with the product both in monolayer and laminated or coextruded structures because of their good chemical resistance and inertness to most foods good barrier properties to water and thermosealability However their polyolefinic nature gives them high lipophilicity enabling retention of large amounts of nonpolar compounds such as most of the aroma compounds thereby causing an aroma imbalance in the packaged food Trace concentrations of residual solvents monomers plasticizers inhibitors or mold-release agents conceivably could migrate to the food product and also flavor ingredients can travel to the package Moreover flavor scalping from the product does not require the product to be in direct contact with the polymer because the aroma compounds are volatile enough to transfer from the headspace to the package Thus although the polymeric films may be adequate moisture or gas barriers for a product these benefits can be offset by flavor scalping Studies in scalping will therefore help determine the type of plastic films best suited for a particular food product (Risch 1991) The frequent use of PE on the inner surface of the food-contact polymer containers has made it the principal polymer in most scalping studies Interaction between Food Flavor and Packaging Material The first and foremost function of a food package is to protect the product and preserve its inherent quality (Nielsen and Jgerstad 1994) Over the past decade the use of plastic packages has increasingly replaced metal and glass for food and beverage packaging the advantages being numerouslower costs lighter in weight less apt to shatter transparent flexible and convenient to the consumer In spite of all these advantages there are some properties of plastics that limit their use in food packaging (Salame 1989) Food packaging interactions defined as an interplay between food packaging and the environment can produce an adverse effect on the food andor the package (Hotchkiss 1997) Interactions between the plastic package and the flavor constituents can cause adsorption and absorption of flavor volatiles by the packaging material permeation of the flavor volatiles through the plastic material food- and flavor-induced changes in the physical properties of the plastic polymer as well as interactions of low-molecular-weight compounds in the plastic such as solvent and plastifiers with the food flavor or the food itself thereby resulting in an overall imbalance in the flavor profile of the food (Gremli 1996) Figure 2 shows the possible interactions between foodstuff polymer film and the environment and their adverse consequences (Nielsen and Jgerstad 1994) Flavor losses that result from interaction with the polymer package can be either losses occurring by permeation or migration through the package or those from sorption by the container (Strandburg and others 1991) Modeling Studies in Flavor Scalping There are several models more aptly theoretical considerations to predict the losses due to flavor scalping Flavor losses that result from interaction with the polymer package can be either losses occurring by permeation or migration through the package or those from sorption by the container (Strandburg and others 1991) The permeation process can be described as a multistep event First collision of the penetrant molecule with the polymer is followed by sorption into the polymer Next migration through the polymer matrix occurs and finally desorption of the permeant from the polymer completes the process For a polymer with thin film geometry Fick's first law can be written aswhere Mxt is the transport rate of the material x through a film of area A with a thickness of L and under a chemical potential created by pressure difference across the film of px P is the permeability coefficient and is a steady-state parameterThe permeability consists of 2 parameters the diffusion coefficient (D) and the solubility coefficient (S) The diffusion coefficient is a kinetic parameter It is a measure of how fast transport events will occur It reflects the ease with which a penetrant molecule moves within a polymer host The diffusion coefficient is determined from the following equation:where L is the film thickness and t12 is the time required to reach one-half the steady-state mass transport rate Once the permeability coefficient and the diffusion coefficient have been obtained the solubility coefficient can be calculated The solubility coefficient is a thermodynamic parameter It is a measure of the concentration of penetrant molecules that will be in position to migrate through the polymerwhere Cx is the concentration in the polymer and px is the partial pressure of x in the vapor phase The sorption of the flavor ingredient from solution onto the polymer involves the process of partitioning and diffusion The mechanism of sorption consists of both adsorption onto the solid surface followed by dissolution into the polymer and diffusion away from the surface under the driving force of a concentration gradient until equilibrium is established The partitioning step involves adsorption onto the polymer surface and mixing into the polymer matrix which depends on the relative forces of attraction between the solution and the polymer for the solute These forces are governed by the thermodynamics of the system and are affected by structure and polarity These factors can be considered on the basis of cohesive energy density (CED) forces or its square root the solubility parameter of the Hildebrand equation The Hildebrand approximation for the heat of mixing iswhere Hm is the partial molar heat of mixing v1 is the partial molar volume of the penetrant 2 is the volume fraction of the polymer in the mixture and 1 and 2 are the square roots of the CED of the penetrant and the polymer The differences in the CED values of the polymer-penetrant combination in a given system will affect the size of heat of mixing and a permeant with a larger CED will have larger heat of mixing and less negative G than the one with a smaller CED The diffusion step depends on the mobility of the solute which can depend on its size and interaction with the polymer to plasticize and relax its chain segments (Halek and Luttman 1991) Organic vapors often solvate host polymers that eventually exhibit increased permeability to oxygen and other gases suggesting that oxygen permeability might provide information on volatile scalping (Salame and Steingiser 1977) In one study limonene absorption by LPDE increased oxygen permeability which was proportional to the limonene concentration (Sadler and Braddock 1990 1991) As oxygen permeability is directly proportional to penetrant concentration MtM will equal PtP where Mt and Pt are respectively the absorbed volatile weight and oxygen permeability of the polymer at time t and M and P are the corresponding volatile weight and polymer oxygen permeability at t If results are expressed as a dimensionless ratio then oxygen permeability can be used to solve mass transfer equations Crank (1967) presented an applicable equation for membrane absorption and desorption (Sadler and Braddock 1990) whereand the absorption equation is (MtM)absorption 1 (MtM)desorption where D is the diffusion coefficient and is the membrane thickness when both surfaces are exposed to the penetrant For single-surface penetrant exposure is the full thickness of the membrane Migration testing using food simulants is the normal procedure for checking compliance of a food packaging material against specific migration limits (SMLs) However as Feigenbaum and others (2002) point out this is not practical for several reasons Industries that put packaged foods or materials intended for food contact on the market do not know the identity of the potential migrants; sometimes those who manufacture and sell these raw materials do not know the processing conditions or the final application; and even if the identity of the migrants were known it may be difficult to analyze them Therefore the use of mathematical modeling to predict migration which can reduce the amount of tests to be undertaken has been recently introduced into legislation Practical examples for the application of this new concept are described in the Practical Guide (European Commission 2003) Mass transfer from a plastic into food consists essentially of kinetic (diffusion in the polymer and foodstuff) and thermodynamic (equilibrium partitioning between the packaging and food) factors besides the geometric dimensions of a given foodpackaging system The most important variables that control migration of the substances are contact time t and temperature T Numerous migration tests have shown that the majority of measurements could be represented as being approximately proportional to the square root of time t and the initial concentration of the migrant in the polymer c P0 With the assumption that material transport obeys the law of diffusion the following equation can be applied to describe approximately the migration of a substance from a polymer into a food (simulant) for situations where mFtmFe 05:DP is the actual diffusion coefficient of the migrant in the polymer with a homogeneous distribution of the migrant at an initial concentration cP0 The constant k is the measure of the influence of factors that lie outside the polymermigrant system and has by definition a value of k 1 in the absence of such influences (such as for contact with ethanol and oil) as long as no polymer swelling takes place A practical application of this equation is that for cases with k 1 the actual diffusion coefficients of migrants in the polymer can be determined from the kinetic measurement of mFt from systems with knownmeasured values for cP0 Provided that the migration potential in the polymer that is the initial amount of migrant dissolved in the polymer mP0 is known thenwhereThe partition coefficient kPF is defined as the concentration ratio at equilibrium of a migrant in the polymer cPe divided by that at equilibrium in the foodstuff or food stimulant cFe The values for kPF range over several orders of magnitude depending on the polarity of the polymer involved the food simulant and the nature of the migrant The kPF value for limonene a nonpolar substance in the LDPEwater system at 23 C was found to be higher than 5000 This makes it retained in the polymer whereas a much more polar compound such as cis-hexenol shows a much lower value of 033 causing considerable transfer into water In recent years the possibility of modeling with easily available hardware and software opens a large field of complex applications MIGRATEST Lite (1997 1999) COATING TEST (1999) and MIGRATEST (2000) are specialized softwares offered for migration modeling (Brandsch and others 2000) Sorption of Food Flavors by the Packaging Materials Sorption of food flavors in polymers involves the process of both partitioning and diffusion Moreover although the intensity of aroma of a packaged foodstuff depends on the vapor pressure (influenced by the other food components) interaction of the volatile organic moieties with other food constituents and aroma barrier characteristics of the package (Mahoney and others 1988) the nature of the aroma is also imperative in determining the extent of sorption The extent of flavor absorption is influenced by the properties of the polymer the flavor molecules and also external conditions The chemical composition chain stiffness morphology polarity and crystallinity of the polymer influence flavor absorption as much as the chemical composition concentration and polarity of the flavor compounds as well as the presence of other chemical constituents External factors such as duration of storage relative humidity temperature and the presence of other food components can also affect the solubility of aroma compounds in a polymer (Nielsen and others 1992a; Leufven and Hermansson 1994) Some of the major factors influencing the scalping process are described in detail below Flavor Characteristics Concentration The higher the concentration of the sorbed material the higher the rate of transport into the polymer structure (Brody 2002) The presence of copermeants can affect the rate of transport of the molecules through the polymer usually by increasing the rate Carbon chain length boiling point and polarity The carbon chain length is closely related to the boiling point of a molecule and several researchers have indicated a relationship between solubility and boiling points of sorbates Thus the carbon chain length of volatiles affects their solubility in polymer films In a sorption study permeation and diffusion of volatile compounds into PE or ethylene vinyl copolymer films were evaluated using volatile compounds such as alkanes aliphatic ethyl ethers aldehydes and alcohols containing 4 to 10 carbon atoms Sorption and solubility coefficient were found to increase with an increase in the carbon chain length of the volatile compounds A study on the sorption behavior of flavor compounds by PE liner of laminated pouches (PETAlPE) containing 43 volatile compounds showed the distribution ratio of the flavor compounds to increase with carbon chain length of the flavor compounds from 001 to 01 for alcohols 003 to 123 for aldehydes 002 to 577 for aliphatic esters and 011 to 116 for benzoates (Shimoda and others 1988) The distribution ratio defined as the ratio of amount sorbed into PE film and the adhesive layer to the amount remaining in the solution with respect to each flavor component was used as the basis of comparison In each series the distribution ratios increased about 3-fold for each methylene group but in the compounds composed of 11 or more carbon atoms the increments were either less or in the case of aldehydes negative The sorption of esters ketones and aldehydes by PP has also been shown to increase as the number of carbon atoms in the compounds increased Moreover compounds with 8 or more carbon atoms were demonstrated to be sorbed from yogurt drinks by HDPE with shorter molecules remaining in the product (Linssen and others 1991) In the same study it was observed that highly branched molecules were sorbed to a greater extent than linear molecules Esters and aldehydes are reportedly absorbed much more than the alcohols in LDPE The absorption of aldehydes has been correlated to their structure the shorter chain aldehyde decanal being absorbed to a lesser extent than the C12 aldehyde and dodecanal The chain length of the lipophilic portion of the molecule appears to affect its absorption the unsaturated aldehydes (for example perillaldehyde and geranial) being absorbed to a lesser extent than the saturated aldehydes (Charara and others 1992) The length of the carbon chain might account for the differences between the esters; the longer the chain the lesser the polarity and ease of absorption of the compounds by the nonpolar polyolefins According to Shimoda and others (1988) the effect of functional groups on the distribution ratios of flavor compounds between a film and a solution was greater in the liquid phase because of closer interactions whereas the effect of molecular weight or boiling point was much larger than the functional group in the vapor phase Strandburg and others (1991) obtained a linear relationship between the logarithm of the solubility coefficient in vinylidene chloride copolymer and the boiling point of linear esters alkanes and ketones Similar results are reported for the solubility of alkyl esters in polyvinyl alcohol (Landois and Hotchkiss 1988) The higher solubility of linalool compared to limonene in PE is also shown to be influenced by its boiling point Linalool is a more linear less bulky molecule than limonene which would facilitate its ability to move into the polymer matrix In addition its higher boiling point (198 C for linalool 175 C for limonene) is indicative of its ability to condense and remain within the matrix (Roland and Hotchkiss 1991) Boiling point has been correlated to higher solubility by several workers Also linalool usually present at 110 the concentration of limonene may have a greater potential in affecting aroma due to sorption by a PE package than limonene The higher solubility of linalool coupled with its higher sensory impact increases the effect of linalool sorption Figure 3 and 4 differentiates linalool and limonene with respect to their structures Solute polarity is one of the predominant controlling factors influencing sorption Flavors are absorbed more easily in a polymeric film of similar polarity The sorption of a number of citrus flavors by LDPE is almost instantaneous the partitioning depending on the polarity of the compounds Comparing carvone (C10H14O) and limonene (C10H16) both similar terpenes but with different polarity it has been shown that the less polar limonene is not only sorbed at a faster rate but also diffuses more rapidly probably due to lesser cohesive forces (Halek and Luttman 1991) In the sorption of citrus oil constituents by polyolefins terpenes showed the highest affinity for the polymers followed by sesquiterpenes (C15); larger amounts of esters and aldehydes were sorbed than alcohols due to polarity (Charara and others 1992) For the same reasons saturated aldehydes were sorbed to a greater extent than those with double bonds Orange juice aromas have been demonstrated to be sorbed to different extents starting with hydrocarbon compounds which showed the highest affinity to LDPE followed by ketones esters aldehydes and finally alcohols (Linssen and others 1991; Nielsen and others 1992a; Linssen and Roozen 1994) Factors that affect absorption include molecular size of the aroma compounds and polarity and solubility properties of both the polymer and the aroma compounds Table 1 shows the solubility parameters and hydrogen-bonding characters of aroma compounds and the polymers used in the study by Nielsen and others (1992b) In general the smaller the difference between values of the polymer and the flavor compound the greater the solubility of the flavor into the polymer Alcohols have much larger solubility parameter values than LDPE LLDPE and PP which might explain why they are less absorbed compared to esters and aldehydes while PET has a solubility parameter closer to that of the alcohols Also polarity and hydrogen-bonding character play an important role in the prediction of solubility The reason why the alcohols are not absorbed to a greater extent into PET might be due to their strong hydrogen-bonding character which PET lacks Esters and aldehydes have solubility parameters very close to LDPE LLDPE and PP which partly explains their large partition coefficient in these polymers The differences between the esters might be accounted for by the length of the carbon chainthe longer the chain the less polar the compounds facilitating easier absorption by the nonpolar polyolefins (Nielsen and others 1992b) Polymer Characteristics Surface area The degree of sorption is directly related to the available surface area in contact with the food (Gremli 1996) Polarity Different plastic materials have different polarity hence they differ in their affinity toward the flavor compounds Flavors are absorbed more easily in a polymeric film of similar polarity (Gallo and others 1999) Polyolefins are highly lipophilic and are incompatible for packaging products with nonpolar substances (such as fats oils aromas) since they can be absorbed and retained by the package (Hernandez and others 2001) The polyesters however are more polar than the polyolefins and hence show less affinity for the nonpolar components Table 2 shows the approximate upper and lower limits for partition coefficients one may normally encounter in plasticfood systems based on the polarities of the solutes plastics and foods (Baner 2000a) It also shows the approximate ranges of partition coefficient values for various solutes between typical food-contact plastics and liquid phases LLDPE and oriented polypropylene (OPP) (both nonpolar) have been shown to easily absorb limonene and myrcene and to smaller extents decanal hexyl acetate nonanone carvone linalool octanol and hexanal (Willige and others 2002a) The flavor molecules carvone and limonene have similar structure but limonene is a nonpolar terpene while carvone is an oxygenated polar terpene Hence limonene is absorbed in larger quantity than carvone Glass transition temperature Sorption rates to a certain extent depend on the glass transition temperature (Tg) of the polymer that determines the flexibility of the polymer molecules Below Tg the polymer molecules are stiff (glassy state) and the chance of a flavor molecule finding a sufficiently large void is limited Above Tg the polymer molecules are highly flexible (rubbery state) which makes this chance higher Table 3 shows the glass transition temperatures of polymers commonly used for food packaging Rubbery polymers such as the polyolefins PE and PP which have a Tg below ambient temperature have a high diffusion coefficient for flavors with steady-state permeation being established quickly in such structures (Giacin and Hernandez 1997) Stiff-chained polymers that have a high glass transition temperature generally have low permeability unless they also have a high free volume (Miller and Krochta 1997) Polymers such as the polyesters PET PC (polycarbonate) and PEN (polyethylene naphthalate) have a Tg above ambient temperature At room temperature these glassy polymers have very stiff chains and a very low diffusion coefficient for flavor molecules at a low concentration Glassy polymers such as polyvinylidene chloride have a low diffusion coefficient for aroma molecules at a low concentration and hence display high flavor-barrier properties (Brody 2002) PEN has excellent performance characteristics in comparison to PET for carbonated beverages allowing hot-fill rewash and reuse due to its high Tg (VanLune and others 1997) Polymer crystallinity Morphological properties that influence permeability and diffusivity include structural regularity or chain symmetry leading to 3-dimensional order or crystallinity (Brody 2002) The more ordered the polymer molecular structure the lower the rate of sorption of the food aroma constituents Crystalline regions can reduce sorption or act as impermeable barriers for diffusion through the polymer They can act as crosslinks to prevent swelling of the polymer The crystalline regions can also restrain polymer segmental mobility affecting the solute permeability to the amorphous regions Thus the degree of sorption for a given solute is often related to the degree of the amorphous polymer content (Charara and others 1992; Letinski and Halek 1992) PP is an example of a crystalline polymer that can exist in various degrees of crystallinity Absorption of limonene and myrcene by PC is found to be much higher than by PET and PEN although the Tg of PC is much higher than the Tg of PET and PEN This is attributed to the lack of crystalline regions in PC which is a totally amorphous polymer (Nielsen 1994) Surface polymer hydrolysis Surface hydrolysis of ethylene-vinyl acetate copolymer can alter sorption behavior While the sorption of hydrocarbons ethyl octanoate and decanal into hydrolyzed EVA film is depressed the sorption of alcohols is promoted This is mainly attributed to solubility of the individual compounds (available from: http://wwwfoodproductdesigncom) Polymer density The amount of aroma compounds sorbed in polymers has been shown to decrease with an increase in polymer density The sorption rate for limonene decreased from 75 to 63 and that of carvone decreased from 17 to 10 when the PP density increased from 08830 gcm3 to 09213 gcm3 respectively (Gremli 1996) Free volume of the polymer The free volume of a polymer is the molecular void volume that is trapped in the solid state (Salame 1989) The permeating molecule finds an easy path in these voids Generally a polymer with poor symmetry in the structure or bulky side chains will have high free volume and hence high permeability A polymer's molecular configuration is altered through solvation by organic penetrants (Takeuchi and Okamur 1976) Use of recycled plastics In an effort to reduce wastes from food packaging materials refillable PET bottles for carbonated drinks have been adopted in many countries A major problem associated with refilling is the sorption of flavors from foodstuffs by the container causing off-flavors in the products filled into the same container The extent of sorption is dependent on temperature the polymer type the carbon chain length and the type of functional groups of the sorbate Washing with sodium hydroxide solutions removes less than half the sorbed amount of terpenes from plastic bottles (Gremli 1996) A study to evaluate the efficacy of washing of PET bottles intended for reuse with sodium hydroxide solution in order to remove limonene linalool and linalyl acetate showed limonene to be significantly sorbed onto the walls of the bottles even after washing (Safa 1999) Recycling of old polymers as new bilayer bottles may be of value if a virgin polymer layer is placed between the recycled polymer and the food The virgin polymer layer plays the role of a functional barrier In the case of solid foods the process of contamination by the recycled polymer is controlled by radial diffusion through the bottle and the food An increase in the volume of the bottle is associated with a decrease in the area of the bottlefood interface per unit volume of food (Rosca and Vergnaud 1998) External Factors pH pH influences the sorption of aroma compounds into the packaging material pH has been shown to affect sorption by a factor of 40 between pH 3 and 5 for 2-hexanal into PE (Leufven and Hermansson 1994) Lowering the pH to 3 increased the sorption of alcohols into LDPE (Nielsen and others 1992a) Sorption of limonene is shown to be 13 times more in LDPE at 22 C and at pH 52 than at pH 26 (Blain 1994) Nonetheless a study on limonene in orange juice showed pH to have no significant effect on scalping (Nielsen and others 1992a) Leufven and Hermansson (1994) studied the interaction of aroma compounds such as trans-2-hexanal 2-heptanone 6-methyl-5-hepten-2-one 6-methyl-5-hepten-2-ol and limonene from tomato juice with polymers such as PET PE and EVOH as a function of pH The amount of extractable aroma compounds in the different polymers at all pH values decreased in the following order: EVOH PE PET Between these polymers the sorption of the aromas was less influenced by pH in PET than in the other 2 polymers where PE contained larger amounts of the compounds at pH 4 than at pH 7 For EVOH there was an increase in sorption of d-limonene with increasing pH Table 4 shows the amount of added aroma compounds sorbed in the polymer films It is hypothesized that pH has a direct relationship with polarity solubility and structure of molecules and can be influenced by them Food composition Food constituents play an important role in influencing the sorption of flavors Not only the type of plastic used is of importance for the uptake of aroma compounds but also the possible interactions between the flavor and food components Flavor components may be dissolved adsorbed bound entrapped encapsulated or retarded in their diffusion through the food matrix by food components The relative importance of each of these mechanisms varies with the properties of the flavor chemical (functional groups molecular size shape volatility and so on) and the physical and chemical properties of the components in the food Proteins carbohydrates and lipids interact with flavors changing the concentration of free flavor in solution and consequently affecting their absorption Absorption of flavor compounds by linear low-density polyethylene (LLDPE) was studied in model systems representing differences in composition of the food matrix The extent of flavor absorption by LLDPE was influenced by food components in the order oil or fat polysaccharides and proteins disaccharides (Willige and others 2000a) Due to the lipophilic character of many flavor compounds food products with high oilfat content tend to lose less flavor by absorption into LLDPE packaging than food products containing no or a small quantity of oil (Willige and others 2000b) The presence of a relative small amount of oil (50 gL) has been shown to decrease absorption substantially Also proteins particularly -lactoglobulin and casein are able to bind flavors resulting in suppression of absorption of the flavor compounds Polysaccharides such as pectin and carboxymethylcellulose increase viscosity and consequently decrease absorption Disaccharides such as lactose and saccharose increase absorption probably by a salting out effect of less nonpolar flavor compounds Selective flavor sorption by packaging materials constitutes a major problem in beverages packaged in PE that has very high affinity for nonpolar compounds Since most beverages are water based the compounds more miscible in PE are absorbed It is hypothesized that by lowering the solution polarity or creating nonpolar regions (emulsified oil droplets) the equilibrium partition coefficient could be reduced thereby increasing flavor retention A study to determine whether oil or sucrose in solution could reduce flavor sorption by PE showed that the sorption and partition coefficient of various compounds into PE were greatly influenced by the presence of oil in solution but not sucrose For compounds most preferentially absorbed by PE addition of oil greatly reduced flavor loss the reduction magnitude being very significant with only 01 oil It is postulated that flavors incorporated into an oleoresin could be used to make beverages resistant to flavor scalping (available from: http://wwwfoodproductdesigncom) Durr and others (1981) reported a 50 loss of limonene from orange juice to LDPE during 2 wk of storage The sorption of limonene by LDPE from model solutions was much greater than that from orange juice attributed to the presence of other constituents in the juice which increased the solubility of limonene in the aqueous phase (Manheim and others 1987) This suggests that the tendency of a beverage to lose flavor might be overcome by the addition of components to the beverage that would reduce the transfer of the individual compounds to the polymer Relative humidity (RH) The presence of water vapor often accelerates the diffusion of gases and vapors in polymers with an affinity for water The water diffuses into the film and acts like a plasticizer opening the polymer structure to molecular transport The solubility of ethyl propionate in polyvinyl alcohol has been shown to reduce with an increase in RH (Landois and Hotchkiss 1988) This is attributed to the competition between ethyl propionate and water molecules for available sorption sites Recently the use of EVOH materials providing a high barrier to organic compounds is gaining much attention as a means to reduce food aroma scalping However although EVOH is an excellent barrier to food aroma when dry a property that even improves at low RH the solubility and diffusivity of the compounds increase dramatically with humidity at medium to high water activity An increase in moisture content of moisture-sensitive plastics such as polyamides or EVOH is reported to increase the rate of permeation of aromatic compounds (Brody 2002) However even at 100 RH EVOH outperforms LDPE as a barrier to organic vapors (Carballo and others 2005) Storage conditions Generally permeability diffusion and solubility coefficients follow a van't Hoff-Arrhenius relationship resulting in increased permeation with an increase in temperature (Brody 2002) Since the effect is accentuated at ambient temperatures compared to refrigerated temperatures the adverse effects have appeared more frequently in foods contained in retort pouches aseptic packages and hot-filled flexible packages The increased flavor absorption at higher temperatures is due to increased mobility of the flavor molecules: changes in the polymer configuration such as swelling or decrease of crystallinity and changes in the volatile solubility in the aqueous phase (Gremli 1996) In 1 study the total amount of flavor absorbed increased considerably with temperature from 4 C to 40 C the absorption by polyolefins such as LLDPE and OPP being several times higher than by the polyesters such as PC PET and PEN indicating polyesters to be more preferable over polyolefins as packaging materials (Willige and others 2002b) Storage temperature has been demonstrated to affect the degree of sorption of aromas by PE Sorption of limonene and myrcene from commercial orange drink stored for 12 wk in PET bottles was found to be 340 and 990 g of limoneneg PET and 011 and 033 g of myrceneg PET at 4 C and 25 C respectively The higher values at 25 C could be due to the greater mobility of the molecules or more swelling of the polymer generating more space for incorporation of the dissolved molecules (Nielsen and others 1992a; Gremli 1996) Similarly the solubility coefficient for aldehyde vapors in linear LDPE was maximal at 25 C with sorption being lower at both 5 C and 75 C (Leufven and Stollman 1992) The sorption of aldehyde vapors by polyvinyl chloride (PVC) also decreased as the temperature decreased VanLune and others (1997) suggested that the crystallinity of PET decreased while free volume increased at higher temperatures resulting in molecules' easier absorption Tawfik and others (1998) demonstrated that PET stored for 15 d at 37 C in a model solution containing 320 ppm limonene absorbed 7 times more limonene than when stored at 5 C but 4 times more after 45 d It is concluded that the diffusion process is temperature dependent as evidenced by the slower rate at a lower temperature Nonetheless absorption of decanal and myrcene by PET film was found to decrease on prolonged storage notably due to desorption from the polymer to the model solution on degradation (Willige and others 2002b) With increasing storage time and temperature degradation of aldehydes such as octanol decanal and citral was also observed in orange juice (Durr and others 1981; Moshanos and Shaw 1989a) Examples of Specific Flavor Systems with Packaging Materials Citrus flavors Citrus flavors which contribute to the flavor of orange juice have been the major subject of study with respect to flavor scalping for quite some time Citrus components from cold-pressed and terpeneless oils have been shown to be absorbed into various polymers such as LDPE HDPE PP and surlyn used in aseptic packaging (Charara and others 1992) Citrus essential oils consist of terpenes sesquiterpenes oxygenated compounds and nonvolatile components while terpeneless oil consists of a higher concentration of oxygenated compounds and a very low concentration of terpenes Table 5 shows the percent absorption of flavors from cold-pressed and terpeneless orange oil extracted from 4 polymers using cyclohexane LDPE has the highest absorption value because of its large amorphous area and low crystallinity the absorption and diffusion taking place in the amorphous area of the polymer Terpene hydrocarbons being lipophilic tend to diffuse into the amorphous regions of the polymers HDPE and PP absorbed constituents to a lesser extent probably due to their higher crystalline structure About 70 of limonene was lost from cold-pressed orange oil in contact with LDPE for 4 d while only a 30 loss was observed from orange oil in contact with HDPE and PP Surlyn was shown to absorb flavor constituents moderately The most extensively studied aroma compound with respect to its sorption by polymers is limonene Limonene is an unsaturated terpene hydrocarbon present in citrus flavors It is a highly nonpolar substance and has shown high affinity for many polymeric packaging materials It is a highly nonpolar substance with high affinity for many polymeric packaging materials A decrease in limonene content in stored orange juice is attributed to its lipophilic nature and hence the ease of its diffusion into the polymer (Moshanos and Shaw 1989b) The absorption of caryophyllene and copeane was lower than that of limonene while that of octyl acetate and sesquiterpenes was similar For limonene in model solutions the affinity onto the polymer is in this order: LDPE polyamide polystyrene Also an increase in the thickness of the polymer film and consequently the mass of the polymer available as sorbent increase the sorption of limonene (Ikegami and others 1991; Pieper and others 1992) The sorption of limonene by LDPE has been demonstrated to be biphasic showing both adsorption and absorption (Halek and Luttman 1991) A study on the flavor absorption by LDPE PC and PET from model solutions containing 7 flavor compounds showed valencene to be almost completely absorbed by LDPE followed to a lesser extent by decanal hexyl acetate octanol and nonanone (Willige van and others 2003) Fewer and less of the flavor compounds were absorbed from the model solution by PC and PET However limonene was readily absorbed from the orange juice by LDPE while myrcene valencene pinene and decanal were absorbed in smaller quantities Berlinet and others (2005) have reported the evolution of aroma compounds from orange juice made from concentrate and stored in glass standard monolayer polyethylene terephthalate (PET 1) multiplayer PET (PET 2) and plasma-treated PET (internal carbon coating) (PET 3) to be due to the high acidity of the matrix implying acid-catalyzed reactions PET packaging materials and their corresponding oxygen permeability were found to have no correlation with the loss of aroma compounds The quality of juices asceptically packed in laminated cartons has been the subject of extensive research during the last decades (Marshall and others 1985; Moshanos and Shaw 1989a 1989b) In another study 2 polyesterpolyolefin adhesive laminates coated with a PVDC-PVC copolymer were surface-exposed to lemon juice and a hot sauce product as well as to food simulant systems at 45 C (Schroeder and others 1990) Sorption of flavor volatiles resulted in delamination of both laminates following exposure to the food products d-limonene being identified as the primary component sorbed by the laminates The shelf life of aseptically filled orange and grape fruit juices has also been shown to be significantly shorter in laminated cartons than in glass jars one of the attributes being the absorption of d-limonene by the PE-contacting surface (Manheim and others 1987) Orange juice packaged in juice board paperboard sandwiched between 2 layers of LDPE has been shown to have a slight turpentine-like off-flavor owing to the absorption of limonene into the paperboard (available from: http://wwwfoodproductdesigncom) The retention of aldehydes ethyl butanoate and other flavor compounds in orange juice is reported to be significantly higher in PET than in HDPE and LDPE (Ayhan and others 2001) Commercially most aseptically filled juices are packed in LDPE-laminated carton packs such as Tetra Brik and Combibloc Food industries often correct the absorptive effect by adding excess flavors to the food for keeping taste and flavor acceptable for consumers until the end of the product's shelf life While flavor absorption may be high enough to affect the sensory quality of a packaged food only a few authors have conducted sensory tests to go along with the analytical results (Kwapong and Hotchkiss 1987; Manheim and others 1987; Sharma and others 1990) Durr and others (1981) showed that the absorption of d-limonene up to 40 did not affect the sensory quality of orange juice during 3 mo of storage at 20 C They suggested that d-limonene contributed scarcely to the flavor of orange juice Moreover they considered limonene absorption even as an advantage since limonene is known as a precursor to off-flavor compounds They also reported the storage temperature to be the main quality parameter for the shelf life of orange juice Apple aroma compounds Evaluation of 5 polymer packaging films with respect to the sorption of 10 apple aroma compounds from its aqueous solution showed major differences in the amount of aroma compounds absorbed by the polymers (Nielsen and others 1992b) LDPE LLDPE and PP absorbed larger quantities of aroma compounds than did the polar polymers PP absorbed larger amounts of aroma compounds than the 2 polyethylenes which may be a consequence of differences in crystallinity and morphology of the polymers LDPE is reported to possess long-chain branching while LLDPE exhibits short-chain branching but similar density and equal heat of fusion and degree of crystallinity Konczal and others (1992) reported larger amounts of apple aromas to be sorbed by LDPE than by EVOH with high ethylene content Migration from Packaging Materials Migration is an important safety aspect to be considered when designing food packaging materials Plastic additives frequently used to improve polymer properties and residual monomers or oligomers are not chemically bound to the polymer molecules and can therefore move freely within the polymer matrix Consequently at the interface between the packaging material and food they can dissolve in the food product and thus adversely affect the flavor and acceptability of the food (Hernandez and Gavara 1999) Some of the additives that are more likely to migrate are the plasticizers used in a range of plastics but more particularly in PVC films where they can migrate in PVC food-contact situations (available from: http://wwwfoodscienceafisccsiroau) While paper and board materials may transmit taint or odor to a food plastics have a much greater potential to do this The presence of monomers can contribute to significant off-flavors styrene monomers at 05 in polystyrene (PS) being responsible for the characteristic plastic odor of many packaged foods Fats and oils in food products however can help mask off-flavors from monomers and odorous residues from plastic processing Nevertheless as consumers shift toward lower fat products off-flavors contributing directly via packaging materials may become more of a problem A number of components of ink may cause unpleasant flavors in food if the manufacture of the packaging material is not carefully controlled Solvents associated with packaging inks and with resins used in bonding the various layers of laminated packaging films can be absorbed by the product to contribute off-flavors (available from: http://wwwfoodprodcutdesigncom) The nature and strength of off-odors migrating to the food depend on a number of factors including the chemical nature of the migrant (its volatility and polarity) the lipophilicity of the food matrix the physical structure of the food (solid compared with liquid) timetemperature conditions during storage and the aroma activity (strength) of the migrant (available from: http://wwwfoodproductdesigncom) Migration of off-flavors from the packaging material could be a result of plasticizers inks and dyes used for graphics or from resins used in the bonding of the package Some factors that could affect migration or be a source of undesirable flavors in the final packaged product are described briefly Molecular weight of the migrant Migration is a term used to describe the process of mass transfer from a food packaging material to its contents If one reduces the migration process to the diffusion in and from the plastics then the migratability of plastic constituents corresponds predominantly to the volatility or molecular weight of these organic substances and to the basic diffusivity of a polymeric type (Franz 2000) For a given plastic this means that the mobility of a migrant decreases with increasing molecular weight Solubility of the migrant in the food matrix Thermodynamic properties such as polarity and solubility influence the migration rate due to interactions between polymer migrant and food stimulant (Helmroth and others 2002) For instance if a migrant has poor solubility in the food simulant it will rather remain in the polymer than migrate into the food simulant This is often the case with nonpolar additives in nonpolar polymers such as LDPE PP and PS in contact with more polar food simulants such as water or 3 acetic acid Higher migration rates are therefore often found for fatty simulants such as olive oil 95 ethanol or isooctane than for aqueous food simulants (Till and others 1987; Riquet and Feigenbaum 1997; Linssen and others 1998) If the food simulant itself has a high affinity for the polymer then it may be absorbed by the polymer Most of the plastic constituents have a lipophilic rather than hydrophilic character and therefore migration increases strongly with increasing fat content and especially so where the fat or oil represents the outer phase of the food matrix (Franz and others 2000) The increase in migration is not necessarily due to an increase in the substance's diffusion coefficient due to interactions between the fat and the plastic as is often assumed (Baner and others 1992) The amount of substances migrating from plastics into foodstuffs with high fat content is higher than in foodstuffs with water content owing to the higher solubility of the migrating organic compounds in fat compared to water In fact the higher the fat content of the product the higher the taste threshold concentration For styrene Bruck and Hammerschmidt (1977) developed an equation that relates the fat content of the food product to the taste threshold concentration as threshold (mgL) 00025 (80 fat in food water in food) Conversely water and products with high water content (juices skim milk) have lower taste thresholds usually on the order of 50 ppm Storage temperature At lower temperatures including refrigeration migration of plastic components to foods may occur the migration being much slower than at higher temperatures (available at: http://wwwfoodscienceafisccsiroau) An understanding of the interactions between food ingredients and polymeric packaging materials requires knowledge of several factors It is worthwhile to examine the relative balance of the various factors and their overall effect on migration Resins as a source of off-flavors Resins used in bonding of paper layers can be a culprit in the migration of off-flavors in packaged foods Quaker Oats Co discovered a pineyspruce off-flavor in packaged ready-to-eat cereals (available from: http://wwwfoodproductdesigncom) that contributed an uncharacteristic flavor note to the cereal When the packaging material used for the outer boxes was examined it did not possess a piney odor but the inner glassine liner contained a strong piney odor The liner was composed of 2 sheets of Kraft paper laminated with a resin in microcrystalline wax and over-waxed on both sides with paraffin wax Odors from inks and dyes Residual solvents from inks and dyes used for packaging graphics can cause off-flavor problems in foods (available from: http://wwwfoodprodcutdesigncom) A nondairy coffee creamer manufacturer noticed shipping boxes of foil-wrapped nondairy creamer to have a severe musty odor Results showed that all of the new production samples contained the odor problem and had a peak identified as 135-trimethylbenzene (mesitylene) The trimethylbenzene peak had a strong musty odor identical to the odor of contaminated boxes Further checking revealed that the packaging supplier had used a new type of ink containing high levels of 135-trimethylbenzene for graphics on the foil packets Inks and model ink components incorporated deliberately into carton boards at low temperature and during microwave heating have shown benzophenone to migrate to the packaged food even from PE-coated boards attributed mainly to the permeability of PE to low-molecular-weight substances (Johns and others 2000) Migration of benzophenone benzylbutyl phthalate butyl benzoate chlorodecane and dimethyl phthalate was also detected after storing the food at 20 C for 1 wk in the impregnated cartonboard It was concluded that for inks used to print food-contact materials the content of low-molecular-weight volatiles should be controlled to lower the migration levels Off-odors from polyamideionomer laminates An off-odor with a smell of cat urine is reported to have occurred in cooked ham products packed in polyamideionomer laminate films (Piringer and Ruter 2000) A gas chromatograph (GC) study of such products was able to identify the presence of diacetone alcohol (DAA) which was used in the printing ink of the film that subsequently migrated into the laminate Dehydration reaction of DAA by the ethylene ionomer resulted in the formation of 4-methyl-4-mercaptopentane-2-one off-odor It is proposed that when printing ionomer films or laminates containing ionomer in which foods with sulfur-containing proteins are packed the absence of mesityloxide and its chemical precursors such as acetone and diacetone alcohol must be guaranteed Styrene taint in dairy products An example of a product that has had styrene taint problems over the years has been dairy products such as coffee creamers and condensed milk packed in thermoformed PS single-serve portion-pack containers the sensory threshold being on the order of 01 mgkg (ppm) of styrene in the product (Baner 2000b) The British Ministry of Agriculture Foods and Fisheries (MAFF 1994) carried out a trade survey of 22 coffee creamer portion packs and found styrene monomer levels in the product ranging from 23 to 223 gkg (ppb) with an average of 134 gkg Of the commonly PS-containing portion-pack materials mono-material PS was found to have the greatest migration followed by PSPE; and the material with the lowest migration was PSEVOHPE Surprisingly even the product packed in PSEVOHPE barrier material contained styrene at a perceptibly significant level at the end of the shelf life despite the EVOH barrier layer between the PS layer and the product The possible explanation for styrene in the product comes from the fact that styrene from the PS layer transfers to the inner PE layer during shipment and storage This takes only a few days given the relatively high diffusion coefficient of PS and PE However lower temperatures and shorter shelf life can reduce the amount of styrene transferred to the product Measurement of styrene monomer migration from PS cups into milk samples containing 05 35 or 10 fat as well as 4 waterethanol mixtures containing 0 15 50 or 100 ethanol indicated that water the simulant prescribed for milk under European Commission legislation (Directive 85572EEC) does not exhibit the required physicochemical properties for an adequate simulation under practical migration conditions (O'Neill and Tuohy 1994) Styrene migration was found to depend strongly upon the fat content of the milk and on the ethanol concentration in the simulant Pure water gave migration values considerably lower than all of the 3 samples of milk and 50 ethanol was shown to correlate approximately with 35 fat milk Styrene migration from PS cups into different food systems such as water milk (05 155 or 36 fat) cold beverages (apple juice orange juice carbonated water cola beer and chocolate drink) hot beverages (tea coffee chocolate and soup with 0 05 1 2 or 36 fat) take-out foods (yogurt jelly pudding and ice cream) aqueous food simulants (3 acetic acid 15 50 or 100 ethanol) and olive oil was also found to be fat dependent the maximum migration being for the fatty foods (Tawfik and Huyghebaert 1998) Studies of styrene migration from PS foam articles have shown the amount of styrene migrating into food oil to be proportional to the square root of the time of exposure (Lickly and others 1995) Cork taint in wines One of the most critical problems in the enological industry is associated with cork taint Significant research has been carried out with respect to cork taint particularly in wines The main compounds responsible for this off-flavor are some chloroanisoles such as 246-trichloroanisole (TCA) 2346-tetrachloroanisole (TECA) and pentachloroanisole (PCA) Tests have confirmed the presence of 246-TCA and 2346-tetrachlorophenol with extremely low-flavor thresholds the dominant odor being close to that of mold (or moldy cork) leaving a sensation of dryness in the mouth very similar to the feeling of a plastic film covering the taste buds (Cantagrel and Vidal 1990) Thus use of compounds containing chlorine in bad conditions in the steps in the manufacture of cork (or in the wine-making process) runs the risk of imparting an off-flavor Off-odors in premiums A common promotional tool is the insertion of premiums inside food packages The volatiles in the inserts if not properly controlled can impart an undesirable flavor to packaged foods Odor testing of unwrapped premiums intended to be inserted in packaged dry mix beverages demonstrated a very strong solvent-like objectionable odor (Apostolopoulos 1998) The source of the residual chemicals was found to be solvents used with either the resin or the paint employed in the manufacturing and painting of the premiums Overwrap films are recommended to prevent direct contact and contamination of the food products Influence of Food Processing on Scalping of Flavors Sorption High-pressure food processing Single-layer and multilayer plastic structures can be used in combination with high-pressure processing (HPP) without concern that the process will enhance sorption In 1 study sorption behavior and flavor scalping potential of selected packaging films in contact with food simulant liquids (FSL) (ethanol and acetic acid solutions) were evaluated after high-pressure processing (Caner and others 2004) HPP treatment (800 MPa 10 min 60 C) showed d-limonene concentration in the films and food simulants to be insignificantly affected by HPP except for the metallized PETEVALLDPE in comparison to the control pouches which were exposed to atmospheric pressure at 60 C for 10 min in an electric oven Irradiation Recently irradiation has been explored as a viable means in the shelf life extension of many foods Apple cider packaged in 3 plastic polymers PS LDPE or nylon-6 (N6) and irradiated at 2 kGy was compared with unirradiated cider packaged in glass containers (Crook and Boylston 2004) The extent of flavor absorption by the packaging materials was influenced by the polarity of the polymer and the flavor compound with plastic polymer having a greater affinity for compounds with similar polarity Cider irradiated and stored in PS containers was shown to have a lower rate of loss than untreated cider or irradiated cider packaged in LDPE for volatile flavor compounds characteristic of the apple or fruity taste and aroma Migration Microwave treatment In the microwave oven plastic containers and wraps are often warmed to a point that plasticizers are released from the plastic into the food (Bishop and Dye 1982) Numerous studies indicate that some plasticizers can cause undesirable side effects in animal tissue and that the amount of migration could be as high as 23 of the total weight In 1 study migration of plasticizers such as dioctyladipate (DOA) from plasticized PVC and acetyltributylcitrate (ATBC) from polyvinylidene chloride (PVDCPVC) (Saran) films into ground meat heated for 4 min was found to be 84 mgkg (147 mgdm2) and 951 mgkg (25 mgdm2) respectively (Badeka and Kontominas 1998) Such migrations could result in deterioration of the final food quality posing off-flavor andor safety problems The migration of compounds from a polymeric material into a food-contacting phase would depend on several factors such as the nature and thickness of the packaging material the nature of the food in contact initial concentration of additives in the polymer compatibility of the additivepolymer system temperature time of contact and others One development in food packaging that has received much attention lately is the microwave susceptor a package developed to meet consumer demands for convenience and quality in microwaveable food products A susceptor is typically a piece of polyester film that has been metallized with aluminum laminated either to paperboard or between 2 layers of paper Foodpackage interactions that result from the use of microwave susceptors and dual ovenable trays have been extensively studied by the US Food and Drug Administration (FDA) 's Indirect Additives Laboratory Susceptors are typically constructed of plastic such as PET adhesives and paper and temperatures in excess of 212 F are common for such packaging At elevated temperatures both volatile and nonvolatile chemicals from the package can migrate into foods (Hollifield 1991) Generally the more paper in the susceptor construction the greater the amount and number of volatile substances released on heating The number of substances released at levels greater than 05 ginch2 of susceptor surface from susceptors containing acrylic-based or vinyl-acetate-based adhesives includes acetone methyl vinyl ketone pentanal toluene hexanal furfural heptanal benzaldehyde nonanal furan isobutanol acetic acid butanol octanal styrene octyl acetate 5-hydroxymethylfurfural and crotonaldehyde (Hollifield 1991) Ionizing radiation Irradiation for the control and reduction of microorganisms and insects and the extension of product shelf life has become a potential preservation technique in many countries Several researchers have studied migration into food simulants describing it to be a consequence of irradiation Lox and others (1991) found an increase in migration as a function of dose up to 10 kGy and a decrease at higher doses from extruded PVC irradiated with 3 to 25 kGy -rays With accelerated electrons the migration increased steadily with the absorbed dose However no significant migration was observed with LDPE and PP at absorbed doses of up to 25 kGy with either electron irradiation or a cobalt-60 -source (Rojas and Pascat 1990) The gas permeability of LDPE HDPE PET and PVC packaging materials is unaffected by irradiation doses of up to 8 kGy (Buchalla and others 1993) However irradiation of these polymers can result in the release of hydrogen CO2 CO and methane gases and the formation of volatile oxidation products including peroxides alcohols aldehydes ketones and carboxylic acids Flexible food packaging materials (LDPE EVAc PETPEVOHPE) irradiated with low (5 kGy corresponding to cold sterilization) intermediate (20 kGy) and high (100 kGy) doses produced these volatile compounds in amounts that increased with increasing irradiation dose (Riganakos and others 1998) The extent of radiation-induced changes depends on many factors such as the type of polymer processing exposure and irradiation conditions (Buchalla and others 1993) Odor intensity values for various polymers have been reported by Tripp (1959) More intense odors on irradiation were observed in LDPE than in HDPE developing stronger off-odors than PS and various polyamides and polyesters The intensity of off-odors of irradiated PE was found to increase with oxygen concentration in the atmosphere with a good correlation existing between the amount of products formed by irradiation and the intensity of off-odor (Azuma and others 1984) The odor-producing volatiles from LDPE films irradiated with a dose of 20 kGy from a 25 MeV electron beam were identified to be mainly aliphatic hydrocarbons aldehydes ketones and carboxylic acids Migration studies with 9 different polymers irradiated at 60 kGy showed increased migration into distilled water for polyamide-6 polyamide-11 polyvinyl chloride-vinyl acetate and poly (vinylidene chloride-vinyl chloride) after -irradiation (Killoran 1972) The extracted substances were identified as low-molecular-weight materials of the polymers and in the case of PVC as an ester-type plasticizer Transfer of off-odors from 2 laminates (with LDPE and HDPE as inner layers) into water was evident at the lowest dose applied (10 kGy) and increased with the absorbed dose to reach a maximum at 150 kGy; however during storage the off-odors gradually disappeared Nevertheless polyester-aluminum-HDPE did not produce any off-odors up to 500 kGy Retorted foods Migration from multilayer laminated film pouches intended for retort foods was investigated using HPLC analysis a fluorescence detector and measurements of residue on evaporation consumption of potassium permanganate and total organic C (Uematsu and others 2005) HPLC analysis revealed that the levels of migrants in oil and water heated in the pouches (121 C 30 min) were 10 times those in the corresponding official simulants n-heptane (25 C 60 min) and water (95 C 30 min) Bisphenol A diglycidyl ether and related compounds were found in oil and water heated in the pouches as well as in the official simulants Results indicate that these compounds were present in the adhesive between the laminated films and migrated through the food-contact film of the package Analytical Techniques Sorption of food flavors In the quantitative analysis of flavor sorption by packaging materials solvent extraction of flavor compounds is generally followed by determination of the extract concentration by GC (Imai and others 1990) Increasing the extract concentration by distillation or vacuum evaporation is usually used to increase the sensitivity of measuring low-magnitude sorption (Kwapong and Hotchkiss 1987) Solvent extraction and multiple headspace extraction using a purge and trap injector (MHE-PTI) can also be used to study sorption While the solvent extraction step is highly tedious and time consuming the MHE-PTI is more convenient rapid fully automated and suitable for volatile aroma compounds The techniques currently employed in the evaluation of flavor sorption include GC-MS (mass spectroscopy) analysis using static headspace sampling dynamic headspace sampling and solid-phase microextraction (SPME) (available from: http://wwwfoodproductdesigncom Paik 1992); solvent extraction coupled with GC (Shimoda and others 1988; Imai and others 1990; Nielsen and others 1992a); electronic nose (available from: http://wwwfoodproductdesigncom) supercritical fluid extraction (SFE) coupled with GC (Nielsen and others 1991; Johansson and others 1993); and vacuum microgravimetry (Roland and Hotchkiss 1991) A novel method developed by Nielsen and others (1991) using supercritical carbon dioxide extraction directly coupled to GC might prove essential in the continuous investigation of absorbed food components in plastic packaging materials It is based on the advantageous properties that carbon dioxide has at a pressure and temperature above the critical point when the carbon dioxide is in the supercritical stage Leufvn and Hermansson (1994) used SFE with carbon dioxide to extract aromas from film samples and deposit them in a chemical adsorbent for thermal desorption onto a GC-FID (flame ionization detection) capillary column Nielsen and Jgerstad (1994) also used SFE to strip the polymer off the sorbed volatiles which was then deposited directly onto a GC-FID capillary column for elution These SFE techniques are limited to aromas that are soluble in the given supercritical fluid (Nielsen and others 1991) In a study on the interaction of orange juice with inner packaging material of an aseptic product the volatile components absorbed by the inner packaging material were extracted by ether and analyzed by GC-MS (Jeng and others 1991) The empty pack after rinsing with deionized water and air-drying was filled with ethyl ether for 24 h at room temperature and the ethyl ether extract so obtained was concentrated with a vigreux column Ethyl cinnamate was added as an internal standard The volatile components so extracted from the inner packaging material were subjected to GC analysis on a Varian 3400 gas chromatograph using a fused silica column with a stationary phase equivalent to Carbowax 20 M In another study using headspace chromatography attempts were made to fingerprint key flavor compounds sorbed by aseptic packages containing juice products (Arora and others 1991) The package that contained juice showed extra peaks in the chromatogram compared to the control container which did not contain any juice The extra peaks represented the uptake of flavor compounds by the package In a study on the sorption of 5 classes of flavor compounds (aldehydes methyl ketones methyl esters alkylpyrazines and sulfur compounds) representing a wide range of food products such as dairy fruit vegetable and meat products by PP at room temperature the PP was cut into small discs and mounted onto a silanized stainless steel wire alternating with silanized glass beads (Arora and others 1991) The stainless steel wire with PP discs and glass beads were inserted into a silanized screw tight glass bottle Each of the glass bottles containing a 2 alcoholic buffer of simulated milk ultrafiltrate (SMUF) and a flavor compound was placed on a shaker for uniform dispersal of the flavor compound for 24 h at room temperature (24 C) Two sets of controls (buffer solution containing only the flavor compound and buffer solution containing the flavor compound wire and glass beads) were placed on the shaker along with the bottles containing the PP samples After 24 h the flavor compound in the buffer solution was extracted with methylene chloride and analyzed by GC The GC analysis was performed using a Supelcowax 10 fused silica capillary column The buffer solution in the controls was also extracted in the same manner as the buffer solution containing the PP discs The quantity of flavor compound extracted was determined using peak areas Calibration curves were generated using peak areas from known concentrations of flavor compounds In the use of refillable bottles such as PET and PC there is a possibility that the bottles returning to the loop could have been used for the storage of detergents pesticides and other chemicals posing a threat of severe contamination problems (Demertzis and Franz 1998) A quick test to predict the sorption properties of refillable bottles involves measuring the uptake of model contaminants onto bottle strips and subsequent remigration of the chemicals in food simulants The model contaminants include alcohol-type compounds such as ethylene glycol phenol n-hexanol 2-phenylethanol menthol and 12-decanediol; esterketone-type compounds such as ethyl acetate cyclohexanone iso-amyl acetate benzopheneone linalyl acetate and methyl stearate; hydrocarbon-type compounds such as toluene n-heptane p-xylene limonene phenyl cyclohexane and phenyl decane; and chlorinated compounds such as chlorobenzene and 111-trichloroethane The GC analytical methodology is usually applied in the detection of the contaminants In the headspace solid phase microextraction (HS-SPME) volatiles are captured by SPME based on the theory of equilibrium partitioning of the analytes between the solid phase of SPME liquid or solid sample matrix and headspace above the matrix and analyzed by GC (Zhang and Pawliszyn 1993) Traditional methods for the extraction and concentration of volatile compounds for analysis by GC such as liquid-liquid extraction solid phase extraction SFE static headspace sampling or dynamic headspace (purge-and-trap) methods have one or more drawbacks such as high cost multistep preparation low sensitivity prolonged extraction time artifact formation or solvent contamination (Braggins and others 1999) Compared to these methods the SPME technique is a simple rapid and economical method requiring no solvents (Yang and Peppard 1994) Nevertheless SPME analysis is reported to be affected by factors such as the nature of the SPME solid phase adsorption time adsorption temperature salt addition stirring condition and sample size (Steenson and others 2002; Lee and others 2003; Rodriguez-Bencomo and others 2003) The oxygen electrode (OE) method provides a rapid and accurate test for gauging the absorption of volatile compounds In a study to measure scalping of limonene by LDPE the LDPE test film was mounted on a YSI 5331 OE The probe was then placed in the headspace of a flask that contained the selected volatile at the test temperature (Sadler and Braddock 1991) Absorption-induced changes in the readings were monitored on a strip chart recorder When stable permeation readings indicated maximum absorption the probe was withdrawn and placed in an air stream equilibrated to the test temperature As the air stream forced desorption of limonene from the probe membrane a strip chart recorder was used to monitor permeability loss in response to desorption Desorption was monitored until the permeation reading was within 5 of its reading prior to volatile treatment Limonene absorption produced an increase in oxygen permeability which appeared to be proportional to limonene concentration Time-course changes in the readings were used to calculate diffusion coefficients of volatiles in the polymer Diffusion coefficients were found to be proportional to the volatile's solubility in the polymer A vacuum-gravimetric method to quantify the sorption of aroma compounds by food-contact polymers developed by Roland and Hotchkiss (1991) consisted of a microgravimetric balance contained in a vacuum chamber Polymer samples were placed on the balance in a sealed chamber and outgassed to 104 torr Small amounts of aroma compounds (d-limonene or linalool) were admitted to the evacuated chamber and the mass increase in the polymer resulting from compound sorption and the pressure within the vessel were recorded by means of a computer This method is proposed to be a useful predictor of individual flavorpolymer interactions at flavor concentrations and amounts that are usually encountered in foods In a method based on weight change in order to study the absorption of citrus flavor volatiles by LDPE tarred LDPE sheets were stored in a closed desiccator over a 50-mL pool of the selected volatile (Sadler and Braddock 1991) After 1 wk the samples were removed weighed and desorbed in a forced-air stream Weight loss was recorded every 15 min until the polymer was within 5 of its weight prior to volatile treatment The solubility of the volatile in the polymer was calculated as:where B and A represented the polymer weights before and after volatile absorption Cava and others (2005) analyzed the diffusion behavior of limonene in LDPE as a function of sample thickness permeant concentration and the outer medium by transmission Fourier transform infrared (FT-IR) spectroscopy A surprising reduction in diffusion (D) and permeability (P) coefficients with reducing film thickness was observed most likely attributed to the morphological differences arising during cast film extrusion Moreover the limonene desorption kinetics were found to slow down considerably when desorption of the volatile was carried out in water compared to desorption in air Finally the sorption kinetics of limonene in LDPE were found to be much slower when the polymer was put in contact with pressed orange juice (similar to a real juice packaging case) than when it was put in contact with the pure volatile A remarkable finding arising from this work is that the diffusion coefficient of limonene in LDPE can vary by up to 2 orders of magnitude depending on the testing conditions mainly limonene concentration but also polymer morphology and consequently these observations may well account for the extensive variability reported for this permeant in the existing literature Migrants from packaging materials With regard to migration the control of transfer from plastic packaging materials into foods is based on the measurement of the substance in the food or simulant The direct migration measurement consists of measuring either directly in foodstuffs or more commonly mimicking as closely as possible a given food packaging application using food simulants The semi-direct migration test applies more severe test conditions by using volatile solvents with strong interactions toward the plastic to enhance the migration rate from the plastic Thus the extraction test is based on accelerated mass transport mechanisms where the diffusion coefficients of migrants are increased by several orders of magnitude compared to the original migration test As a rule extraction tests are designed such that they make use of the following principle: polar polymer polar migrant polar solvent worst case nonpolar polymer nonpolar migrant nonpolar solvent (Franz and others 2000) When an off-odor problem occurs and is suspected to be packaging related it is suggested that the packaging supplier be approached to find out the nonproprietary aspects of the components used during manufacture The next step is to obtain an analytical profile of the product typically done using dynamic headspace GC-MS while simultaneously conducting taste and odor evaluation To confirm that the off-flavor problem is indeed packaging related a control should be run where the product is stored using a relatively inert barrier such as glass Finally one needs to look for volatiles that correlate with the defect and find their threshold levels If off-flavor increases over time then it would be best to look for alternative packaging materials or packaging materials with different barrier compositions In general the first stage in the determination of the migrants in polymers is their separation from the matrix When the migrant is a volatile compound such as styrene the headspace GC technique is very suitable for the analysis; it has been used in the EU project Specific Migration by heating the PS dissolved in dimethylacetamide at 90 C for 120 min If the migrant is a nonvolatile compound it is essential to use a liquid extraction step The solvent used should both dissolve the target compound and also swell or dissolve the polymer matrix When the polymer is dissolved in a solvent the polymer is then usually reprecipitated by addition of a solvent in which the polymer is insoluble Usually extraction procedures are carried out with hand shaking (Garcia and others 2006) Nevertheless sometimes ultrasonics (Marque and others 1998) or maceration (Monteiro and others 1998) could be employed to improve the process Gramshaw and Vandenburg (1995) used dynamic headspace to extract styrene from thermoset polyester passing through the U-tube nitrogen at 25 mLmin and heating the oven at 200 C To analyze styrene dimers and trimers Soxhlet extraction with dichloromethane was used followed by size exclusion chromatography to clean up the dichloromethane extracts Chromatographic separations in the gas and liquid phases are currently state of the art (Brandsch and others 2000) In the automatic PTI coupled to a GC used for the dynamic MHE of volatile compounds from aqueous solutions as well as films trapped volatiles after the purge time are thermally flash desorbed and directly injected onto the GC column (Feigenbaum and others 1998) In 1 study the source of an off-odor in premiums intended for use with dry mix beverages was evaluated in accordance with the ASTM F 151-86 (ASTM 1986) method using headspace GCmass spectrometry (Apostolopoulos 1998) The premiums were placed in Mason jars which were sealed with Teflon-lined lids equipped with sampling ports The Mason jars containing the premium samples were placed inside a mechanically convected oven and heated at 110 C for 90 min to ensure vaporization of the premium residuals into the headspace of the Mason jars Using a preheated gas-tight syringe to avoid condensation of the volatiles headspace aliquots of 1 mL were withdrawn from the Mason jars and injected into GC-MS equipped with a CP-Sil 8 CB chromatographic column operated at 20 C for 2 min and then increased at 10 Cmin to 250 C The compounds present in the injected aliquots were separated in GC-MS scans with mass spectral identifications GC-MS was also used in the identification of volatiles produced during electron beam irradiation (Riganakos and others 1998) About 12 to 16 g of packaging materials was weighed into glass headspace vials sealed and irradiated Helium gas at a flow rate of 30 mLmin was passed for 20 min through the headspace vials maintained at 80 C The volatile compounds were collected on a Tenax GC plug filled into the glass liner of an Optic PTV-Injector The headspace gas chromatographic (HSGC) method for determining volatile substances emitted from high-temperature food packaging is used to screen microwave susceptors and fatty food simulants (McNeal 2000) Levels of butadiene in a food or food simulant are usually determined by HSGC with automated sample injection and by FID (Franz and others 2000) HS-SPME coupled to GC-electron capture detection can be used for the direct determination of chloroanisoles in wine samples (Urunuela and others 2004) Additional selective methods of considerable importance include direct mass spectrometry using an electro-spray-ionization (ESI) or atmospheric pressure ionization (API) ion source which can quickly provide data for several species migrating into a stimulant in 1 run The ESI-MS is especially well suited for complex nitrogen-containing and phenolic structures; combinations of HPLC with ESI-MS or AI-MS also provide a very powerful tool An analytical procedure based on headspace GC and mass selective detection is usually used to determine volatiles whereas HPLC with UV detection is quite suitable for determining potential migrants of high molecular weight such as PET oligomers and adhesive plasticizers arbitrarily classified as nonvolatiles (Hollifield 1991) Total migration of components from packaging materials into fat-releasing foodstuffs is based on the determination of the weight of a sample of the packaging material before and after its storage in a test fat under standard conditions a correction being applied for the residual fat retained inon the sample (Figge and others 1978) The latter may be determined by physical or chemical methods the calculation being based in most cases on a single component of the triglyceride mixture that has migrated into the sample With most test fats differential migration of the individual components of the fat into and incomplete extraction of the absorbed fat from the test polymer are serious sources of error Fewer problems are associated with the use of 14C-labeled HB 307 as the fat simulant suitable for all types of plastics including the highly crosslinked and insoluble types A reference material for the determination of overall migration from a plastic coextrudate into the fatty food simulant olive oil was produced and certified in an interlaboratory study (Lund and others 2000) The analyses were carried out according to the ENV 1186 standard from the European Committee for Standardization (CEN) with exposure of the coextrudate to olive oil for 10 d at 40 C After an initial preliminary interlaboratory study 8 laboratories participated in the certification round and 2 different methods were used to obtain single-sided exposure of the plastic to the oil A reference value of 86 mgdm2 to 14 mgdm2 (half width of the 95 confidence interval) was obtained which is within the range relevant for the regulatory limit (10 mgdm2) making this reference material suitable for laboratories measuring according to the EU overall migration limit A neutron activation method developed for the analysis of HDPE LDPE PP PET and PS food-contact plastics provides for determination of over 50 elements at a concentration of below 1 mgkg (Thompson and others 1996) This technique has now been extended to study migration from food-contact materials into standard food simulants (olive oil acetic acid ethanol and water) Samples of plastic are irradiated in a thermal neutron flux to produce radionuclides of the elements present in the plastic Over a period of time the radionuclides of these elements may travel from the plastic into the food simulants and hence migration can be determined Gamma ray spectrometry performed on the simulants at the end of the test is used to quantify the migration any activity being attributed to the migration of radionuclides of elements in the plastic Detection limits of about 0002 mgkg were achieved for antimony (Sb) in retail PET bottles It is imperative that every analytical method adopted for migration studies be capable of reaching the required detection limit typically 50 parts per billion or less (Buck and Bussey 2002) To verify whether the methodology is capable of delivering the correct results FCN (Food Contact Notification) rules state that each analytical method be validated Extracts of samples or controls must be spiked with the potential migrant at known levels and then analyzed using the same method applied to the sample extracts Adequate recovery of the spiked material shows that the method works as reported While chemical analysis guides the search for off-flavor contributors in a food identifying these also requires sensory evaluation tools Legislation A major concern in packaging is whether the packaging components will migrate into the food product In addition to concerns about the safety of a packaged food packagers must also address concerns about whether the packaging will affect appearance flavor odor and other factors influencing consumer acceptance According to FDA regulations any packaging material that comes in contact with food must receive FDA clearance before it can be used (Buck and Bussey 2002) While consumer acceptance issues will determine the success or failure of a given product unsafe packaging is a public health issue and will affect the future of the food and packaging manufacturers Package component migration can result in food adulteration which violates government laws and food safety professionals must be aware of regulations pertaining to this area The major purpose for performing migration studies is to estimate exposure to food packaging components (Begley 2000) Exposure is calculated to determine an estimate of daily intake (EDI) The EDI for a particular migrant is compared with the acceptable daily intake (ADI) of the migrant as determined by FDA toxicologists In addition to positive lists and SMLs general provisions have been introduced under the European Community Directive controlling the suitability of materials and articles on the basis of overall migration limits Also European Council Directive 82711EEC as amended by European Commission Directive 938CEE (European Commission 1993) establishes in Article 3 that verification of compliance of migration into foodstuffs with the migration limits shall be carried out under the most extreme conditions of time and temperature foreseeable in actual use Time and temperature are 2 factors that affect the migration of substances from plastic materials in addition to other factors such as compression stacking or vacuum packing that should be taken into account when carrying out migration tests under the worst foreseeable conditions The transfer of substances is regulated by 200272 with 2 different migration limits that is overall migration limit and SML The overall migration limit the total quantity of substances released by the sample is 60 mgkg or 10 mgdm2 Some substances are also regulated with SML because toxicological data submitted to the Authority are limited or its impact in higher transfer level is considered to be a concern SMLs are mentioned in Annex II of 200272EC The Plastic Materials and Articles in Contact with Food Regulations 1998 set an overall migration limit for all food-contact plastics the limit being 10 mgdm2 of plastic surface area in general However a limit of 60 mgkg of food applies specifically in the case of containers or similar receptacles with a capacity between 05 L and 10 L or which have a contact area that cannot be determined and for sealing devices such as caps gaskets and stoppers (available from: http://wwwfoodgovuk) The Australian Food Standards Code has set maximum migration levels for 3 specific monomers vinyl chloride acrylonitrile and vinylidene chloride because of their known potential toxicity (available from: http://wwwfoodscienceafisccsiroau) A packaging material with exceptional importance for foods is PE Depending on the source of this plastic water in contact with it can produce characteristic flavor changes The description of the PE odor ranges from candle-like stuffy musty to soapy to rancid For this reason PE used for food applications has high-quality standard requirements Another packaging material for which toxicity and safety have been extensively studied is styrene which is reported to have no health consequence at the levels commonly found in foods The current European legislation sets no SMLs for styrene in food which means its content is controlled by the overall migration limit of 60 mgkg in the food The overall migration limit is never reached because styrene creates a strong astringent chemical plastic off-taste at levels much lower than the 60 mgkg Recent surveys of styrene levels in foods by the MAFF in England have led to the conclusion that there is no toxicological concern considering the levels (1 to 134 gkg) found in foods (MAFF 1994) Approaches to the Reduction of the Scalping Process Judicious selection of polymers is the best way to reduce scalping by the use of crystalline polymers polymer blends or edible films (Gallo and others 1999) Fluorination of polymer surface and inert coatings on the polymer surface is yet another approach Some of the common measures to prevent the scalping process thus maintaining the integrity of the packaged food items are described below Flavor encapsulation Protection mechanisms designed into commercial flavor delivery systems provide for release of the flavor at the appropriate time Advances in encapsulation technology allow encapsulation of hydrophobic or hydrophilic flavors which are available in a range of particle size shape and solubility Flavors can be encapsulated to protect them from undesirable interactions with the components and the package The industry is developing micro- and macroencapsulation technologies utilizing various coatings such as polymers waxes fats starch hydrogenated vegetable oils proteins maltodextrins mono- and diglycerides gum arabic alginates gelatin and cellulose compounds (available from: http://wwwfoodproductdesigncom) Electron beam irradiation Electron beam irradiation of ethylene vinyl acetate copolymer films is shown to markedly depress the sorption of flavor compounds such as hydrocarbons and low-polarity compounds (Matsui and others 1990) This effect is attributed to the radical reactions evolving changes in the structural characteristics such as crosslinking and scission reactions (Lawton and others 1960) Selective scalping Few researchers have addressed how scalping particularly selective scalping can improve the flavor profile of food systems Polymer blends included with an agent that has an affinity for specific compounds can be used to proactively remove deleterious substances in a packaging environment (Del Nobile and others 2002) The possibility to trap degradation products (produced by chemical reactions) with scavengers such as a zeolite additive or antioxidants and hence prevent degradation products from migrating to the polymer film surface and further into food in contact with the film was investigated by Anderson and Forsgren (2005) Adsorption of oxidative degradation products in a zeolite additive or protection of LDPE by using antioxidants could prevent off-flavor in the packed product such as water The migration of low-molecular-weight compounds formed during polymerization processing and forming of packaging materials could be a problem For example acetaldehyde is formed in the polyester PET by the thermal decomposition of the ethylene glycol hydroxyl terminal group and the main chain of the polymer (Ikgarashi and others 1989) In their study poly (m-xylidene adipamide) (nylon MXD6) D-sorbitol and -cyclodextrin aldehyde-scavenging agents were blended with poly (ethylene terephthalate) and thermally pressed into films The total amount of aldehydes sorbed by the films was 2 to 10 times higher for films containing the aldehyde-scavenging agents than nonblended films Aldehyde-scavenging films demonstrated selective scalping preferably for smaller-molecular-weight aldehydes Odor absorbent packaging can also be used in combination with base polymers such as PET LDPE and PP to eliminate off-odors produced during long-term storage (Perchonok 2003) The odor-producing compounds targeted could be aldehydes and ketones associated with lipid oxidation and cooked odors Ketones are found in beverages and foods such as ultra-high temperature (UHT) milk The use of polymeric amines in packaging to remove volatile food components may be an effective means to remove unpleasant flavor notes since ketones and aldehydes contain functional carbonyl groups that readily react with amines Choice of packaging material The choice of plasticizers must be made on the basis of the film's end use A possible approach to reduce the potential for migration of plasticizers from PVC into foods is to replace monomeric with polymeric plasticizer compounds of higher molecular weight with reduced tendency for migration due to limited mobility in the polymer matrix for example a polyadipate ester-type plasticizer used at 70 level for low-molecular-weight PVC or 50 level for a high-molecular-weight PVC (Demertzis and others 1990) Vinylidene chloride polymers Vinylidene chloride polymers are often used in connection with other structural polymers as a barrier to prevent the entry of oxygen into food containers and to limit flavor scalping during long periods of storage Although these polymers display outstanding characteristics for use in food packaging they suffer from sensitivity to thermal treatments undergoing heat-induced degradative dehydrochlorination at process temperatures of 150 170 C To scavenge evolved hydrogen chloride and thus prevent the formation of metal halides by interaction with extruder walls these materials are usually blended with a small amount of passive base prior to processing (Howell and Uhl 2000) Biobased food packages resistant to scalping In general plastic materials are not inert and where direct contact between the packaged product and the plastic container occurs there can be migration of substances into the product The amount of any component that migrates into food depends on the original concentration of the particular component in the polymer and its solubility as well as the temperature mechanical stresses and contact time Therefore there is a considerable interest in replacing some or all of the synthetic plastics by biodegradable materials in many applications Polylactic acid (PLA) has finally arrived as an alternative to PET PVC and cellulosics in some high-clarity packaging roles PLA an aliphatic polyester featuring high-clarity gloss stiffness and easy processing is fabricated by polymerizing lactic acid monomer (LA) produced by carbohydrate fermentation of corn dextrose Currently PLA is being used as a food packaging polymer for short-shelf-life products with common applications such as containers drinking cups sundae and salad cups overwrap and lamination films and blister packages (Ikada and Tsuji 2000) The novel resin is forging roles in thermoformed cups and containers and also single-serve drink bottles Synthesized from processed corn a renewable plant feedstock it biodegrades after use if composted PLA synthesis requires 30 to 50 less fossil fuel than polymers synthesized from hydrocarbons and thus reduces carbon dioxide emission These green benefits could provide users with a marketing edge Nonetheless PLA faces hurdles including its high density (125 gcc) relative to PP and PS It also has high polarity making it difficult to adhere without tie-layers to nonpolar PE and PP in multilayer structures But the greatest stumbling block is PLA's cost currently an average of 130lb Notably PLA delivers a balance of properties that has generated enthusiastic interest from some end users A good example of PLA's early success is a biaxially oriented PLA (BOPLA) film made by Mitsubishi Plastics in Japan This BOPLA film is laminated to paperboard in a golf-ball package for Dunlop Japan The reverse-printed PLA film becomes the clear viewing window when a panel is die-cut out of the paperboard BOPLA film laminates easily and justifies Dunlop's recyclable-compostable claims PLA and PHB (polyhydroxy butyrate) bottles or cups could be used for packaging fresh unpasteurized orange juice (Haugaard and Festersen 2000) PLA cups have relatively low water vapor permeability and high resistance to scalping compared to PE Since PHB has a much lower oxygen transmission rate than PLA (Krochta and De Mulder-Johnston 1997) and PHB has high water resistance (Hanggi 1995) coating of PLA with PHB is expected to give a useful biobased packaging material for beverages Packaging materials based on 100 PHB are also expected to be useful for beverages One major concern for biobased packaging materials is that they are moisture-sensitive To assure food safety it is advised that these packages be tested under the worst condition of 100 RH for the full anticipated shelf life Recently the application of the nanocomposite concept was shown to be a promising option to improve mechanical and barrier properties of packaging films (Avella and others 2005) Nanocomposite films were obtained by homogeneously dispersing functionalized layered silicates (clay minerals) in thermoplastic starch via polymer melt processing techniques These films were made by using different starch matrices such as potato starch and a mixture of potato starch with biodegradable polyester In the case of starchclay nanocomposites a good intercalation of the polymeric phase into clay interlayer galleries together with good mechanical parameters such as modulus and tensile strength was obtained Moreover the conformity of the starchclay nanocomposite films with actual regulations and European directives on biodegradable materials assessed demonstrated that these materials could be utilized in the food packaging sector owing to their low overall migration limit Packaging for wines and liquors Closure types vary considerably in scalping properties and may cause considerable changes in flavor concentration in wines (Capone and others 2003) Closures tested included screw caps natural cork closures a technical cork closure and 7 synthetic closures Semillon wine samples spiked with various aroma compounds including pyrazines oak-related phenols ethyl esters of fatty acids monoterpenes or hydrocarbons and sealed with the closures under test were stored for 2 yr No absorption of any of the flavor or aroma compounds on the screw caps was observed Relatively nonpolar compounds were absorbed by cork or synthetic closures The more polar compounds were not absorbed by any of the closures For the nonpolar compounds absorption was greatest for the synthetic closures; technical cork closures performed similarly to the natural corks but had a slightly higher absorption capacity For pale ale bottled in clear PET and PEN containers with plastic caps and a glass control bottle with a crown closure sensory and physicochemical properties at the 14th wk showed PEN bottles to have provided the best protection followed by glass and finally PET (Goodrich 1997) Packaging for aseptic foods Aseptic foods are packaged in a variety of polymeric materials The PE liner in brick type aseptic containers scalps d-limonene geranial octanal and decanal from juice products (Arora and others 1991) As a result the packaged fruit juice lacks flavor notes characteristic of fresh juice There are reports of 62 and 37 sorption of nonpolar and polar organics respectively by PP PP is ranked second after PE in the quantity of flavor compound sorbed Juices packed in coextruded PP containers consisting of PP outer and inner layers surrounding an internal EVOH layer have shown a marked decrease in d-limonene content compared to juices packed in foil containers due to sorption A layer of Saran is suggested with PP and HDPE to reduce the sorption of d-limonene (Arora and others 1991) Commercial scalping-resistant packaging options Some commercial packaging materials are specifically designed to circumvent the problems usually associated with flavor scalping For juices International Paper Co (Memphis Tenn USA) has introduced a new generation of Super-Marketing beverage packaging for juice and milk products which helps lock in vitamins and retain flavor longer International Paper's patented Barrier-Pak (R) technology reduces flavor oil scalping by up to 20 preserving the fresh taste of juice products The Lisle Ill based EVAL Co of America recommends the use of EVOH in direct contact with juices to reduce flavoraroma migration (available from: http://wwwfoodproductdesigncom) EVOH provides an effective barrier even in the presence of moisture as flavor molecules are significantly larger than oxygen molecules EVOH is not considered a recyclable material; however 0001 inches of EVOH provides the same barrier protection as 45 inches of HDPE (available from: http://wwwfoodproductdesigncom) It is advocated to use either PEpaperboardPEtie layerEVOHtie layerPEtie layerEVOH in direct contact with the juice or a slightly simpler structure consisting of PEPPtie layerEVOH The barrier is an excellent way to protect juice from losing flavor and aroma compounds Also a relatively simple structure of HDPEtie layerEVOHtie layerEVA protects against flavor migration McLean Marketing has announced a new concept in packaging for Uncle Matt's organic juices The company is offering its organic orange juice in PET bottles that are claimed to offer many advantages which for consumers could translate into better juice quality and taste plus an easy to recycle container The PET packaging produces better juice quality over the life of the product providing a better oxygen barrier with less flavor scalping Polymer nanocomposites have been demonstrated to help achieve packaged food a shelf life of 3 to 5 yr (Perchonok 2003) Aegis OX polymerized nanocomposite oxygen-scavenging barrier nylon resin specially formulated for high oxygen and carbon dioxide barrier performance even in high humidity is commercially available for a host of co-injection molded PET bottle applications including bottles and orange juice containers Another grade Aegis NC can be used as a coating or as the base resin for cast or blown films and replace nylon 6 coatings in paperboard juice cartons The new family of resins nearly doubles the heat resistance of nylon 6 and has a potential for less flavor scalping For wines and liquor A clear high-barrier film that creates a superior oxygen barrier to protect wine packaged in bag-in-box wine casks is now available from Scholle Corporation (Chicago Ill USA) a supplier of wine bags worldwide (available from: http://wwwbagnboxcom) This film replaces the traditional metallized PET film that used to be standard in the wine industry It essentially doubles the shelf life of the wine resists puncturing and flex-cracking and can withstand the rigorous transportation conditions required for export DuraShield is now being used in wine-producing countries worldwide Using the latest polymer technology it reduces flavor scalping However Flextank a world leader in using PE for wine aging maintains that food-grade PE of any density will retain its porosity in the presence of wine for many years resisting clogging by wine components or scalping flavor from the wine Cleartuf Power Polyester Resin (MG Polymers USA LLC Tortona Italy) is a PE terephthalate copolymer resin designed for liquor packaging and custom-packaging applications It is a high-molecular-weight polymer designed to provide highly desirable container properties for the one-way packaging of tunnel-pasteurized beers (available from: http://wwwmgpolymerscom) These include high clarity and sparkle increased temperature and pressure stability reduced flavor scalping reduced carbon dioxide loss due to creep and reduced carbon dioxide and oxygen permeability Cleartuf Power Polyester Resin is designed with a special catalyst and stabilizer system that offers property retention during processing Miscellaneous options Honeywell Specialty Films (Morristown NJ USA) has announced the commercialization of Aclon a polychlorotrifluoroethylene (PCTFE) resin for use in multilayer containers Aclon provides the moisture barrier and chemical resistance properties of PCTFE in resin form for the blow-molding of flexible and rigid plastic packaging Incorporated as a contact layer in multilayer extrusions Aclon has successfully demonstrated the barrier properties needed to improve the shelf life and reduce flavor scalping of liquids Fabri-Kal (Kalamazoo Mich USA) a thermoformer of semirigid plastic packaging has a patented approach for incorporating desirable aromas in thermoformed cups bowls tubs and trays (Brody 2005) The aromas can be engineered for release by an integer of trigger-time opening of the container microwaving and so on And the reverse removal of undesirable aroma by activated carbon has been developed at the Univ of Georgia with funding by Soldier Systems (Natick Mass USA) CompelAroma developed by ScentSational Technologies LLC is another patented and proprietary encapsulated-aroma release technology The Jenkintown Pa based company incorporates specially engineered FDA-approved food-grade flavors into microwave trays and other food and beverage packages (Bertrand 2005) The flavors which are generally recognized as safe by the Flavor and Extract Manufacturers' Assoc are incorporated within the polymetric structure of thermoformed packaging at the time of molding These heat-stable flavor additives withstand the high heat histories that plastic packaging experiences during extrusion and thermoforming and while cooking in the microwave Although this technology is beneficial to most foods that are microwaved it benefits foods that lack flavor and aroma needed to satisfy the consumers' taste buds Conclusions As consumers look for better-tasting and ready-to-eat foods the food industry will continue to develop new packaging options to meet consumer needs With these proliferating options comes the challenge of living up to consumer expectations of safety and wholesomeness of the packaged food item There is ample evidence that sorption of flavor constituents and migration of odors from the packaging material alter the overall flavor profile of a packaged product Recent advances in molecular modeling simulations serve as an attractive tool to verify and subsequently identify the most accurate mechanism for sorption and migration As new packaging materials are developed and new applications are found for the existing materials further research must be performed 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flavor analysis J Agric Food Chem 42 ( 9 ): 1925 30 Zhang Z Pawliszyn J 1993 Headspace solid-phase microextraction Anal Chem 65 ( 14 ): 1843 52 ABSTRACT:Food packaging although an integral part of the food chain has a major drawback in that often the packaging material interacts with the flavor constituents of the food causing either a selective or an extensive loss of desirable food flavors or absorption of undesirable off-flavors from the packaging material thereby resulting in an eventual loss of quality of the packaged food item The process is called scalping and is of great concern to the food industry which is always looking out for new avenues in packaging solutions for its final product quality needs The review highlights the various attributes of the scalping process explores approaches to the reduction of the manifested undesirable effects and covers other relevant aspects |