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Chapter 13

Meat Packaging

Maurice G. O ’ Sullivan and Joseph P. Kerry

Introduction

The packaging of muscle - based foods is necessary to ensure that such products reach the consumer in a condition that satisfi es his or her demands on a number of levels, namely: nutrition, quality, safety, and conve-nience, as well as the ability to deliver a product shelf life that will endure the stresses of handling, transportation, storage, sale, and consumer contact. However, in order for such products to be truly commercially suc-cessful, consumer desires and demands must be addressed and met with respect to the sensory properties of such products, before other quality dimensions become relevant (Chambers and Bowers 1993 ). The three sensory properties by which consumers most readily judge meat quality are: appearance, texture, and fl avor (Liu et al. 1995 ). Each food product category presents its own unique challenges in this regard, and meat is no different. Unfortunately, fresh meat color is short - lived and surface discoloration that occurs during chilled and frozen storage is considered a sign of unwholesomeness and product deterioration (Faustman and Cassens 1990 ). The bright, cherry - red color of fresh beef is used by consumers as an indicator of meat quality (Cassens et al. 1988 ; Kennedy et al. 2004 ). In red meats, consumers relate the bright red color to freshness, while dis-criminating against meat that has turned brown in color (Hood and Riordan 1973 ; Morrissey et al. 1994 ). It is because of such sensory quality changes in fresh meat

that so much attention has focused on devel-opments within the area of packaging tech-nologies, especially in the last twenty to thirty years. In the case of beef, two impor-tant visual clues that determine perceived quality are color and packaging (Issanchou 1996 ).

There are four categories of preservative packaging that can be used with raw muscle foods. These are vacuum packs (VP), high oxygen modifi ed atmosphere packs (high O 2 MAP), low oxygen modifi ed atmosphere packs (low O 2 MAP), and controlled atmo-sphere packs (CAP) (Gill and Gill 2005 ). Over the past number of years, much research has focused on the infl uence of modifi ed atmosphere packaging (MAP) on meat quality attributes and the purchasing prefer-ences of consumers (Carpenter et al. 2001 ; Jayasingh et al. 2002 ). Discoloration in retail meats during display conditions may occur as a combined function of muscle pigment oxidation (oxymyoglobin to met-myoglobin) and lipid oxidation in membrane phospholipids (Sherbeck et al. 1995 ). MAP is one of the principle methods of maintain-ing and prolonging meat color sensory quality.

High O 2 concentrations promote the oxy-myoglobin (OxyMb) cherry red form of myoglobin (O ’ Grady et al. 2000 ) but may impact negatively on the oxidative stability of muscle lipids and lead to the development of undesirable fl avors (Rhee and Ziprin 1987 ; Estevez and Cava 2004 ). The breakdown products of lipid oxidation have been associ-

Handbook of Meat Processing Edited by Fidel Toldrá

© 2010 Blackwell Publishing. ISBN: 978-0-813-82182-5

248 Chapter 13

Modifi ed Atmosphere Packaging of Meat Products

MAP is defi ned as “ a form of packaging involving the removal of air from the pack and its replacement with a single gas or mixture of gases ” (Parry 1993 ). MA packs usually contain mixtures of two or three gases: O 2 (to enhance color stability), CO 2 (to inhibit microbiological growth), and N 2 (to maintain pack shape) (Sorheim et al. 1999; Jakobsen and Bertelsen 2000 ; Kerry et al. 2006 ). An example of MA packed meat is presented in Figure 13.1 . The capacity for such gases to promote the overall quality of fresh red meat is well established (Gill 1996 ). Beef steaks are commonly displayed under high oxygen concentrations in MAP in order to promote color stability (Zakrys et al. 2008 ). The color of lamb may also be extended by storage under MAP conditions (Kerry et al. 2000 ).

MAP has now been available to producers for many years. As far back as 1933, Killefer (1930) , using 100% carbon dioxide (CO 2 ) at 4 – 7 ° C, found that pork and lamb remained fresh for twice as long as equivalent products

ated with the development of off - fl avors and off - odors and loss of color in meat (Faustman and Cassens 1989 ).

A variety of packaging systems and tech-nologies are currently available for muscle foods. Fresh red meats may simply be placed on trays and over - wrapped with an oxygen - permeable fi lm, or placed within a gaseous - modifi ed atmosphere. As the meat industry moves toward central processing that employs MAP and vacuum packaging, they may need to overcome consumer preference for fresh beef that is bright red in color and packaged with the traditional PVC over - wrap (Carpenter et al. 2001 ).

Finally, the changing faces of ecologically friendly packaging require the addressing of multiple aspects of packaging, including recyclability, simple packaging, reusable, refi llable, renewable materials, less materi-als, less or no plastics, and bulk rather than individual packaging (Doyle 2008 ). Also, the noncontact preservative effect of active packaging offers the opportunity to produc-ers of prolonging shelf life further, while maintaining the clean label status of meat products.

Figure 13.1. Modifi ed atmosphere packed meats, beef burgers, and beef steak. Gas mixtures 80% oxygen and 20% CO 2 .

Meat Packaging 249

order to maintain bloom, with at least 20% CO 2 to prevent selective microbial growth (Eilert 2005 ). Whether these gases were placed in the primary package or in a master bag surrounding the primary package, the basic technology has been unchanged for a number of years. This technology has been successful for a number of larger retailers, as the shelf life provided by this package has been suffi cient for usage in a controlled dis-tribution system (Eilert 2005 ). High O 2 MA packs contain atmospheres of O 2 and CO 2 , and often N 2 . Mixtures of O 2 /CO 2 have been used commercially for a considerable time (Brody 1970 ). A patent in 1970 specifi ed a range of O 2 and CO 2 concentrations suitable for MAP beef (Georgala and Davidson 1970 ). Results demonstrated that at least 60% O 2 is required to achieve a color shelf life of 9 days, and the patent claims that a mixture of 80% O 2 plus 20% CO 2 keeps meat red for up to 15 days at 4 ° C (Georgala and Davidson 1970 ). Typically, fresh red meats are stored in MAP containing 80% O 2 :20% CO 2 (Georgala and Davidson 1970 ), while cooked meat equivalents are stored in 70% N 2 :30% CO 2 (Smiddy et al. 2002 ).

Beefsteaks are commonly displayed under high oxygen concentrations in MAP in order to promote color stability (Zakrys et al. 2008 ). As previously stated, the major func-tion of O 2 is to maintain the muscle pigment myoglobin in its oxygenated (oxymyoglobin) form (Kerry et al. 2006 ), but high oxygen levels within MAP also promote oxidation of muscle lipids over time (O ’ Grady et al. 1998 ). These high O 2 levels may also impact negatively on the oxidative stability of muscle lipids and lead to the development of undesirable fl avors (Rhee and Ziprin 1987 ; Estevez and Cava 2004 ). This distinctive off - fl avor develops rapidly in meat that has been precooked, chilled - stored, and reheated. The term warmed - over - fl avor (WOF) has been adopted to identify this fl avor deterioration (Renerre and Labadie 1993 ). Membrane phospholipids are particularly susceptible to

stored in air and held at similar temperatures. Also, the shelf - life extension of bacon by packaging in CO 2 - enriched atmospheres was investigated by Callow in 1932 (Callow 1932 ). Additionally, in the 1930s a carbon dioxide - enriched environment was employed to transport refrigerated beef carcasses from Australia and New Zealand (Floros and Matsos 2005 ). The retail use of MAP did not occur until the 1950s, in the form of vacuum packaging (Floros and Matsos 2005 ). In 1981, Marks & Spencer introduced to the United Kingdom gas - fl ushed fresh meat in plastic trays (Inns 1987 ). It is now used ubiq-uitously across the meat industry for many different meat products. As previously stated, MA packs usually contain mixtures of two or three gases.

The use of high O 2 concentrations in MA packs promotes oxymyoglobin (OxyMb) for-mation, the cherry red form of myoglobin (O ’ Grady et al. 2000 ). Packaging beef in MA packs and storing at low temperatures extends the product shelf life considerably (Young et al. 1983 ). Beef and lamb are both red meats and share similar properties, but con-siderable differences in shelf lives are apparent between them due to their relative susceptibility to chemical and microbial spoilage. In contrast to beef cuts, much of the surface of lamb is adipose tissue, which has a pH close to neutrality and has no signifi cant respiratory activity (Robertson 2006 ). The pH of beef is lower than that of lamb, thus making it less susceptible to microbial spoil-age (Gill 1989 ; Kerry et al. 2000 ). In order to optimize shelf life, sensory quality, and microbiological safety using MAP, the pack-aging system applied must be product spe-cifi c (Church and Parsons 1995 ).

High O 2 MAP Meat Packs

The vast majority of meat products have been and continue to be offered in high oxygen pack formats (approximately 80% O 2 ) in

250 Chapter 13

the correct blend of gases that maximizes initial color, color stability, and shelf life, while also minimizing microbial growth, lipid oxidation, and gaseous headspace (Mancini and Hunt 2005 ). Jakobsen and Bertelsen (2000) reported that while O 2 levels higher than 20% were necessary to promote meat color, package O 2 contents higher than 55% did not result in additional color stabi-lizing benefi ts.

High O 2 concentrations can cause protein oxidation, which has been linked to increased toughness in MAP meat, particularly beef. Thus, protein oxidation may decrease eating quality by reducing tenderness and juiciness, and enhancing fl avor deterioration and dis-coloration (Xiong 2000 ). Zakrys et al. (2008) showed that high O 2 concentrations in MAP - stored beefsteaks were shown to have increased toughness scores after cooking, as determined by 134 consumers (Fig. 13.2 ; Zakrys et al. 2008 ).

oxidation processes, thereby causing the rapid development of meat rancidity (Renerre 1990 ). The oxidation of polyunsaturated fatty acids not only causes the rapid development of meat rancidity, but also affects the color, the nutritional quality, and the texture of beef (Kanner 1994 ).

High O 2 - MAP increases lipid oxidation in meat: beef (Jakobsen and Bertelsen 2000 ; Zakrys et al. 2008 ; Zakrys et al. 2009 ), pork (Lund et al. 2007 ), and lamb (Kerry et al. 2000 ). High - oxygen atmospheres (80% O 2 ) also promote pigment oxygenation, and therefore, prolong the time before metmyo-globin is visible on the muscle surface. The drawback to high O 2 MAP is that although it maintains redness during storage, rancidity often develops in the meat while color is still desirable (Jayasingh et al. 2002 ). Because consumers use meat color as an indicator of freshness and wholesomeness, recent advances in MAP have focused on fi nding

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Figure 13.2. An overview of the variation found in the mean data from the ANOVA - partial least squares regression (APLSR) correlation loadings plot for each of the 5 MAP treatment groups: 40%, 50%, 60%, 70%, and 80% oxygen, with all packs containing 20% CO 2 and the make - up gas N 2 . Shown are the loadings of the X and Y variables for the fi rst 3 PCs for raw data. • = days and MAP treatments, � = sensory descriptor and instrumental variables. The concentric circles represent 100% and 50% explained variance, respectively. (Adapted from Zakrys et al. 2009 .)

Meat Packaging 251

concluded that the use of 0.4% CO during storage in MAP improved beef color without masking spoilage. Upon removal of product from CO packaging, meat color (likely to be a combination of COMb and OMb) deterio-rated during display in a manner not different from product exposed only to air. Thus, the inclusion of 0.4% CO in conjunction with O 2 will not infl uence color stability, metmyo-globin - reducing activity, or O 2 consumption. This is likely the result of greater formation of oxymyoglobin (oxyMb) in atmospheres containing 20 – 80% O 2 , which dominates or limits the ability of carboxymyoglobin (COMb) to form (Seyfert et al. 2007 ). COMb is more resistant to oxidation than oxymyo-globin, owing to the stronger binding of CO to the iron - porphyrin site on the myoglobin molecule (Wolfe 1980 ). However, one of the main consumer fears relating to the use of CO is the possible loss of quality due to a break in the cold chain, causing deteriora-tion in spite of its attractive appearance (Wilkinson et al. 2006 ). Concern has been expressed in the United States in the past that such a system would mask spoilage that could occur in fresh meat products (Eilert 2005 ). The FDA noted that while color did not degrade in a package containing CO, offensive odors could still form normally in the product in the presence of CO (FDA 2004 ). Although there are distinct advantages for the storage and display life of meat with CO in VP or low O 2 MAP, consumers have a negative image of CO because of its haz-ardous nature and the concern that products may appear fresher than they actually are (Cornforth and Hunt 2008 ). The declaration of CO for meat as generally recognized as safe (GRAS) in the United States has a legal basis (Boeckman 2006 ). The use of CO in the primary package of fresh meat in the United States is a major breakthrough. This will allow for the wider distribution of case - ready products and adequate shelf life needed to achieve distribution of these products (Eilert 2005 ).

Carpenter et al. (2001) showed that con-sumer preference for beef color was suffi -cient to infl uence their likelihood to purchase, but was not enough to bias taste scores. It is likely that once a decision to purchase beef is made in the market, whether the beef is presented in the form of cherry red fresh - bloomed beef, the brown of discounted beef, or the purple of vacuum - packaged beef, con-sumer eating satisfaction at home will depend only on the beef quality attributes of tender-ness, juiciness, and fl avor (Carpenter et al. 2001 ).

Low O 2 MAP Meat Packs

Low O 2 packaging systems have been readily available for usage in the United States, but are not as widely implemented as their high O 2 counterparts (Eilert 2005 ). Low O 2 MAP are generally packed with CO 2 (usually enough to dissolve into the product) and also N 2 , while residual O 2 may be present or included during the packing process. The CO 2 acts as the antimicrobial and N 2 as the pack shape stabilizer (S ø rheim et al. 1997 ). For Low O 2 MAP in the United States, carbon monoxide (CO) may also be used as a gas for meat color enhancement. Within the EU, only Norway adopted the use of CO (0.3 – 0.5%) in primary packs in the mid 1980s; however, this practice has since ceased, following a decision by the EU Parliament committee in 2004 not to allow the use of CO in meat packaging applications (S ø rheim 2006 ).

Industrially, CO has been added to pack-ages to eliminate the disadvantages of com-mercial ultra - low O 2 MAP, because CO has a high affi nity for myoglobin and forms a bright cherry red color on the surface of beef (S ø rheim et al. 1999 ; Luno et al. 2000 ; Jayasingh et al. 2001 ; Hunt et al. 2004 ). CO is a colorless, odorless and tasteless gas. It is produced mainly through incomplete com-bustion of carbon - containing materials (S ø rheim et al. 1997 ). Hunt et al. (2004)

252 Chapter 13

(Dixon and Kell 1989 ). The absorption capacity is related to biological factors (i.e., pH, water, and fat content) (Gill 1988 ; Jakobsen and Bertelsen 2002 ), but also to a large extent to packaging and storage con-ditions, specifi cally CO 2 partial pressure, headspace to meat volume ratio, and storage temperature (Jakobsen and Bertelsen 2002 ; Zhao et al. 1995 ). O ’ Sullivan et al. (2010) used sensory panelists to assess the prefer-ence of steaks packed under atmospheres containing 50% O 2 (50 CO 2 ), 70% O 2 (30 CO 2 ), 80% O 2 (20 CO 2 ), or 100% CO 2 . The principal aim of this study was to explore off - fl avors developed by CO 2 in commercial MA packs as well as 100% CO 2 . Samples were tested by assessors after immediate cooking, upon removal of the respective packaging, and a second identical sample set was served with samples left for 30 minutes in ambient air to let any CO 2 dissipate prior to cooking. From sensory analysis, panelists had a preference for steaks packed under atmospheres containing 50% O 2 . The 50% O 2 packed treatments displayed a signifi cant ( P ≤ 0.05) and negative correlation with CO 2 fl avor, and this was even more pronounced for samples where the CO 2 was allowed to dissipate (Dis, P ≤ 0.001). There also appeared to be a directional correlation of the 100% CO 2 samples to CO 2 fl avor, although these results were not signifi cant (Fig. 13.3 ). All other treatments proved to be nonsignifi -cant. One explanation for this may be the leanness of the meat used in this study, which had a very low fat content. In addition, the meat purchased was very stable in terms of composition, with no signifi cant variation in protein, fat, and moisture content. These cuts are typical of those found in Irish supermarkets.

In general, CAP is used for bulk product or items of irregular shape, such as whole lamb carcasses, or as master packs for retail - ready product (Gill 2003 ). CAP is not suit-able for individual trays of retail - ready product because of the undesirable color of

Controlled Atmosphere Packaging of Meats

The storage life of chilled meat can be extended by packaging the product under controlled atmosphere packaging (CAP) with N 2 or CO 2 (Gill and Molin 1991 ). The absence of O 2 in an O 2 - free MAP or CAP system results in a signifi cant shelf - life extension, as these packaging formats offer hostile envi-ronments to obligate aerobic spoilage micro-organisms. CAP packaging has been used commercially for the shipment of chilled lamb to distant markets (Gill 1990 ).

However, these packaging systems initi-ate the development of metmyoglobin in the meat, which is unattractive to the consumer (Hunt et al. 1999 ). The meat will bloom to an attractive bright red color shortly (20 – 30 min) after opening the pack and exposing the meat to air. Another negative attribute associated with these packaging formats is that the high usage of CO 2 may cause off - fl avor or CO 2 taint in the meat, which can be detected upon consumption (Nattress and Jeremiah 2000 ). CO 2 is highly soluble in water, most of which is contained in the muscle, and also in fat tissue. This solubility is increased with decreasing temperature. When an atmosphere rich in CO 2 is used, the high solubility of the gas in meat tissues must be taken into account (Gill 2003 ). In an atmo-sphere of 100% CO 2 , meat will absorb approximately its own volume in gas. Thus, the initial gas volume must exceed the required fi nal volume by the volume of the enclosed meat (Gill 2003 ). When high CO 2 levels are applied in a package headspace, the concentration of CO 2 will decline due to absorption of CO 2 in the meat. CO 2 dissolves in meat until saturation or equilibrium is reached. CO 2 is also suspected of affecting the chemical quality of the meat (Jakobsen and Bertelsen 2002 ). A lowering of meat pH is a result of CO 2 absorption into the meat and is a consequence of carbonic acid being dissociated to bicarbonate and hydrogen ions

Meat Packaging 253

Vacuum Packaging of Meat

Vacuum packaging (VP) was one of the ear-liest forms of MAP methods developed com-mercially and still is extensively used for products such as primal cuts of fresh red meat and cured meats (Parry 1993 ). An example of vacuum packed meat is presented in Figure 13.4 . The fi rst signifi cant commercial appli-cation was for vacuum packaging of whole turkeys using rubber stretch bags (Purdue 1997 ). VP extends the storage life of chilled meats by maintaining an O 2 defi cient envi-ronment within the pack (Bell et al. 1995 ). Vacuum packs are comprised of evacuated pouches or vacuum skin packs, in which a fi lm of low gas permeability is closely applied to the surface of the product. Preservative effects are achieved by the development of an anaerobic environment within the pack

anoxic meat, and because packaging materi-als that are impermeable to gases are mostly opaque (Gill 2003 ). The inclusion of O 2 in CAP systems at low levels can have a delete-rious effect on meat color. The inclusion of just 100ppm oxygen can cause this discolor-ation, but this is usually transient, since the metmyoglobin is reduced to myoglobin, usually within four days, as anoxic condi-tions are established and maintained (Gill and Jones 1994 ). However, O 2 scavengers may be used in CAP systems to prevent the formation of metmyoglobin, if very low levels of O 2 are accidentally incorporated during pack fi lling. Buys (2004) found that the inclusion of an oxygen scavenger ensured that retailed bulk - packaged pork chops held in approximately 100% CO 2 were still accept-able to a consumer panel after 14 days of storage.

Figure 13.3. An overview of the variation found in the mean data from the ANOVA - Partial Least Squares Regression (APLSR) correlation loadings plot for each of the 4 MAP treatment groups. Shown are the loadings of the X and Y variables for the fi rst 2 PCs for � = days and the individual MAP treatments, • = sensory descriptor and instrumental variables. Im (Immediate) = meat samples cooked immediately after opening of the MA packaging and presented to panelists. Dis (Dissipate) = meat samples left 30 min in ambient air to let any CO 2 dissipate, then cooked and presented to panelists. The concentric circles represent 100% and 50% explained variance, respectively. (Adapted from O ’ Sullivan et al. 2010.)

254 Chapter 13

The consumer has been shown to reject those myoglobin forms that are not acceptable meat colors from their perspective (Parry 1993 ; Allen et al. 1996 ). Consumers have demonstrated a bias against the purchase of vacuum packaged beef, which displays the purple color of deoxymyoglobin (Meischen et al. 1987 ). Also, prolonged storage of meat in vacuum packs results in the accumulation of drip, which is also unappealing to consum-ers (Jeremiah et al. 1992 ; Parry 1993 ; Payne et al. 1997 ).

VP continues to be used in numerous ways for effi cient meatpacking and is still the most cost - effective packaging strategy employed for the packing of meat. A recent innovation in VP has been the evolution of shrinkable fi lms in use with horizontal form - fi ll - seal machinery (Salvage and Lipsky 2004 ).

Vacuum Skin Packaging of Meat

Drip formation in vacuum packed meat, as discussed above, can partly be overcome by vacuum skin packaging (VSP), using a fi lm that fi ts very tightly to the meat surface, leaving little space for the accumulation of

(Gill and Gill 2005 ). The objective is that any residual O 2 in the remaining atmosphere, including O 2 dissolved in the product, will be removed by enzymatic reactions within the muscle tissue, or through other chemical reactions with tissue components (Gill and Gill 2005 ). Respiration of the meat in vacuum packs will also quickly consume the vast majority of residual O 2 , replacing it with CO 2 , which eventually increases to 10 – 20% within the package (Taylor 1985 ; Parry 1993 ; Gill 1996 ). However, the amount of O 2 remaining in the pack at the time of closure must be very small if the product is to be effectively preserved, as the capacity of the muscle tissue for removing O 2 is limited (Gill and Gill 2005 ). The oxygen level is generally reduced to less than 1% under good vacuum conditions. Due to the barrier properties of the fi lm used, entry of oxygen from the outside is restricted (Parry 1993 ; Robertson 2006 ).

Vacuum - packaged meat is unsuitable for the retail market because depletion of O 2 , coupled with low O 2 permeability of the packaging fi lm, causes a change in meat color from red to purple, due to the conver-sion of oxymyoglobin to deoxymyoglobin.

Figure 13.4. Vacuum - packed meat products, chorizo and salami.

Meat Packaging 255

gives rise to active packaging (Camo et al. 2008 ). An active package was defi ned by Rooney (1995) as a material that “ performs a role other than an inert barrier to the outside environment. ” They can actively control microbial contamination of foods during storage and distribution. The fundamental concept behind this technology is the incor-poration of an antimicrobial agent into the packaging material by either spraying, coating, physical mixing, or chemical binding (Berry 2000 ). Food manufacturers may be able to maintain the minimum inhibitory con-centration of an antimicrobial to prevent growth of pathogenic and spoilage microor-ganisms by using controlled - release packag-ing (Koontz 2006 ). The major potential product applications for antimicrobial fi lms include meat, fi sh, poultry, bread, cheese, fruits, vegetables, and beverages (L ó pez - Rubio et al. 2004 ).

Antimicrobial (AM) packaging research generally started with the development of antimicrobial packaging materials that contain antimicrobial chemicals in their mac-romolecular structures (Han 2005 ). Chemical preservatives can be employed in antimicro-bial - releasing fi lm systems, including organic acids and their salts (sorbates, benzoates, and propionates), parabens, sulfi tes, nitrites, chlorides, phosphates, epoxides, alcohols, ozone, hydrogen peroxide, diethyl pyrocar-bonate, antibiotics, and bacteriocins (Ozdemir and Floros 2004 ). Antimicrobial fi lms can be classifi ed into two types: (1) those that contain an antimicrobial agent that migrates to the surface of the food, and (2) those that are effective against the surface growth of microorganisms without migration (Suppakul et al. 2003 ). Also, antimicrobial coatings may be developed by incorporating nisin, lactoferrin, sodium diacetate, sorbic acid, and potassium sorbate into a coating material (Limjaroen et al. 2003 ). Antimycotics and antimicrobials have been added to food pack-aging fi lms to delay outgrowth of mold. Potassium sorbate release from low - density

any fl uid exudate (Hood and Mead 1993 ). This style of package uses a polystyrene or polypropylene tray, coupled with the use of a barrier fi lm that can form around the product to reduce any liquid purge emanating from it. An additional web of fi lm or a header can also be added for pre - pricing and pre - labeling. Depending on one ’ s perspective, an advantage or disadvantage of this package is that it gives the product a very unique appear-ance (Belcher 2006 ). VSP involves produc-tion of a skin package in which the product is the forming mold. It was fi rst introduced using an ionomer fi lm, which softens on heating to such an extent that it can be draped over sharp objects without puncturing (Robertson 2006 ). The product shelf life can be 15 – 22 days, depending on the meat cut used. Since the product is displayed in the myoglobin state, there is no loss of color in the display case and oxidation issues are minimized using this packaging format (Belcher 2006 ).

In summary, VSP eliminates the wrinkled appearance of traditional vacuum - packaged meat products, thus improving the appear-ance of products, which will have a positive effect on consumer appeal.

Active Packaging

Antimicrobial packaging is a promising and rapidly emerging technology in which anti-microbial agents are incorporated into or coated onto food packaging materials to prolong the shelf life of the packed food, usually by extending the lag phase and reduc-ing the growth rate of microorganisms (Floros et al. 1997 ; Han 2000 ; Suppakul et al. 2003 ). The aim of active packaging is to increase the display life of the contained products, while maintaining their quality, safety, and sensory properties, without direct addition of active agents to the product (Camo et al. 2008 ). Inclusion of the active agents, be they antioxidants, antimicrobials, or any other, within the packaging material

256 Chapter 13

dation in beef, leading to the enhanced display life of the meat. Additionally, Camo et al. (2008) investigated and compared the effect of two natural antioxidant sources (rosemary and oregano extracts) incorpo-rated into an active package fi lled with a modifi ed atmosphere on the display life of lamb steaks. These workers found that a rose-mary extract, a rosemary active fi lm, or an oregano active fi lm resulted in enhanced oxi-dative stability of lamb steaks. Also, active fi lms with oregano were signifi cantly more effi cient than those with rosemary, exerting an effect similar to that of the direct addition of the rosemary extract and extended fresh odor and color from 8 to 13 days compared to the control.

Active packaging has the advantage of maintaining the preservative effects of various compounds (antimicrobial, antifun-gal, or antioxidant), but without being in direct contact with the food product. This is an important development, considering the consumer drive toward clean labeling of food products and the desire to limit the use of food additives.

Summary and Future Trends in Meat Packaging

In recent years, much attention has focused on the shift from consumers buying meat at the family butcher shop to purchasing it at the local supermarket. More and more tradi-tional butcher shops have closed because they cannot compete on price, offer the same supermarket one - stop shop opportunity, or provide the extended shelf life of MAP meats to the consumer that are available on refriger-ated supermarket shelves. This is the situa-tion in most developed countries, particularly within the EU, where sales of fresh meat have increased in supermarkets at the expense of the specialized butcher ’ s store (Mannion 1995 ). However, recently, consumers have become very much more discerning with respect to the origins of the food they

polyethylene (LDPE) and high - density poly-ethylene (HDPE) fi lms has been studied in food systems. In such systems, release rates and migration amounts must be closely mon-itored for the system to effectively preserve the contents of the package (Han 2000 ). Looking to the consumers ’ demand for chemical preservative - free foods, food man-ufacturers are now using naturally occurring antimicrobials to sterilize and/or extend the shelf life of foods (Han 2005 ). Present plans envisage the possible use of naturally derived AM agents in packaging systems for a variety of processed meats, cheeses, and other foods, especially those with relatively smooth product surfaces that come in contact with the inner surface of the package. This solution is becoming increasingly important, as it represents a perceived lower risk to the consumer (Nicholson 1998 ). Various bacte-riocins, such as nicin, pediocin, lacticin, pro-pionicin, etc., can be incorporated into foods and/or food packaging systems to inhibit growth of spoilage and pathogenic microor-ganisms (Daeschul 1989 ). The extracted bacteriocins, which are generally small molecular weight peptides, can be utilized in various ways; however, it is very important to characterize their resistance to thermal treatment and pH (Han 2005 ). The storage temperature may also affect the activity of AM packages. Several researchers have found that the protective action of AM fi lms deteriorated at higher temperatures, due to high diffusion rates in the polymer (Vojdani and Torres 1989 ). The diffusion rate of the AM agent and its concentration in the fi lm must be suffi cient to remain effective throughout the shelf life of the product (Cooksey 2000 ).

Antioxidant packaging is a recent devel-opment in active packaging technologies that has had some success. Ner í n et al. (2006) described the promising results of a new anti-oxidant active packaging system; a plastic fi lm with an embodied rosemary extract was able to inhibit both myoglobin and lipid oxi-

Meat Packaging 257

beef that is bright red in color and pack -aged with the traditional PVC overwrap. Nevertheless, it is encouraging that the initial perceptions of quality will likely not bias eating satisfaction once a decision to pur-chase is made and the meat is taken home, thereby hastening the acceptance of the newer packaging technologies (Carpenter et al. 2001 ). Additionally, meat processing and packaging technologies that are accepted by the market and adopted by the industry will have to become more effi cient, consis-tent, and leaner in activity if future global challenges are to be met. Low - oxygen pack-aging technologies will continue to evolve as long as they can successfully and economi-cally enable the wider distribution of cen-trally packaged fresh meat (Eilert 2005 ).

It is critical that we understand the factors that will have the largest infl uence on the evolution of meat packaging. The demand for convenience foods will continue to be fueled by the aging of our population, the diminished cooking skills of the typical con-sumer, and the reduced time available for home preparation of meals. The ability of materials to offer fl exibility in primary pro-cessing as well as reheating at home will be critical (Eilert 2005 ).

The volatility of oil prices has a direct effect on the cost of traditional petrochemi-cal - based packaging materials. Also, the environmental considerations of disposing of traditional packaging after use have become center stage in recent years with respect to green solutions to modern living. The increased costs of petroleum will continue to drive the demands for bio - based packaging materials. Consumer demand for more envi-ronmentally friendly packaging and more natural products will also create increased demand for packaging from biodegradable and renewable resources (Cutter 2006 ). Even though food manufacturers cannot eliminate packaging, they can redesign packages to reduce the amount of material used or to incorporate newly developed materials such

consume. Poor labeling by the supermarkets has resulted in a swing back toward the local butcher, where meat traceability is transparent and promoted as a selling point; in addition, green issues relating to product movement to markets (air miles) and support for local product producers has encouraged this same trend. The impact of such develop-ing trends on the pre - pack sales of meat at the supermarket level remains to be seen.

Mize and Kelly (2004) reported the trends in fresh meat packaging at retail level in the United States. They found that in 2002, 69% of the linear footage of the self - service meat case was occupied by fresh meat and poultry. This fi gure declined to 63% in 2004, refl ect-ing a growing conversion of meat items to products with greater consumer convenience, such as fully cooked entrees and marinated meats, as well as hams and sausages. They also reported an increase in packages that were case ready, from 49% in 2002 to 60% in 2004.

As stated earlier, high O 2 MAP is now used ubiquitously across the meat industry for many different meat products. Alternatively, low O 2 packaging systems have been readily available in the United States, but not as widely implemented as the high O 2 counterparts. Vacuum packaging continues to be, in many cases, the most cost - effective packaging strategy. A relatively recent innovation in vacuum packaging has been the evolution of shrinkable fi lms in use with horizontal form - fi ll - seal machinery (Salvage and Lipsky 2004 ). This packaging format uses a polystyrene or polypropylene tray and uses a barrier fi lm that can form around the product to reduce any amount of purge coming out of the product. An addi-tional web of fi lm or a header can also be added for pre - pricing and pre - labeling (Belcher 2006 ).

As the meat industry moves toward central processing that employs MAP and Vacuum - Skin Packaging (VSP), processors may need to overcome consumer preference for fresh

258 Chapter 13

“ NatureTray ” product aimed at fresh meat. Both these companies use a foam form that is derived from 100% annually renewable resources. In the future, we can hope to see even more applications for renewable pack-aging materials in the packaging of meat products. These products will address the various technical challenges of MAP and vacuum packaging and overcome the gas permeability issues required to make such packaging effective.

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as biodegradable plastic in their products ’ packaging. This is particularly important in the European Union, where many countries are considering tougher legislation to encour-age the use of less packaging material (Dodds 2007 ). Biopolymer fi lms may serve as poten-tial replacements for synthetic fi lms in food packaging applications to address strong marketing trends toward more environmen-tally friendly materials, but hydrophilicity is a central limitation to replacement and full-scale commercial utilization of biodegrad-able fi lms (Han et al. 2005 ). However, a variety of bio - based materials have been shown to prevent moisture loss, reduce lipid oxidation, improve fl avor, retain color, and stabilize microbial characteristics of foods (Cutter 2006 ).

Additionally, any assessment of the envi-ronmental impact of food packaging must consider the positive benefi ts of reduced food waste in the supply chain (Marsh and Bugusu 2007 ). The demand for pre - packaged fresh meat will continue to grow, but it is critical that packaging formats that enable wider distribution of these products evolve (Eilert 2005 ). Foamed food trays made of polylactic acid (PLA) resin, the corn - based biopolymer, have recently been trialed in the United States and Europe for commercial meat packaging applications (Schut 2008 ). The polymers are said to biodegrade when packages that are made from them are com-posted. Moisture and heat in the compost pile break the PLA polymer chains to smaller chains, and then ultimately to lactic acid. Microorganisms in the compost consume the lactic acid for nourishment (Nachay 2008 ).

An Italian company, Coopbox SpA in Reggio, which is a major producer of foam food packaging, introduced the fi rst foamed PLA trays, called Naturalbox, in 2005, which can be used for the packaging of meat, fi sh, or poultry. Also Cryovac Inc. (Reading, Pennsylvania) has commercialized a PLA foam tray in the U.S. market with its

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