The oldest method of packaging and distributing fresh poultry meat is in a “wet shipper.” The wet shipper is a wax-coated corrugated box in which whole birds are placed with ice (Figure 6.1). The “dry shipper” is similar to the wet shipper with ice excluded. More recently, whole carcasses have been placed in polymer bags and sealed or clipped (Figure 6.2). Almost 90% of all chicken parts are packaged directly into consumer portions using highly oxygen permeable polystyrene foam trays with a high oxygen permeable PVC or polymer-based, stretch film overwrap. These include breast, thigh, drum, and wing por- tions (Figure 6.3). Most of the remaining portion of poultry meat is packaged in bulk ice packs at the central processor, but it ultimately ends up in a similar tray and stretch wrap package at the retail level (Figure 6.4).
Figure 6.1 “Ice-pack” broilers packaged in a wax-coated corrugated box, “wet-shipper.” (Courtesy of Mountaire Farms, Selbyville, DE.)
In a bulk pack system described by Timmons,3the retail packages are placed in corru- gated containers with plastic liners. The liner is then gas-flushed with a modified atmos- phere and sealed within the corrugated container (Figure 6.5). This system provides approximately five additional days of shelf life, compared to the non-modified atmosphere packaging method. A low oxygen barrier material such as HDPE/LDPE co-extrudate is used to allow release of off odors produced during storage. Due to the concern for buildup of off odors in the package, high barrier film materials have limited use in the poultry industry. Only about 1–2% of poultry meat requires high oxygen barrier packaging, includ- ing precooked products. Other requirements of fresh/frozen poultry packages are non-fog- ging, non-wrinkling, high clarity, puncture resistance, and sealability.
Poultry parts can be deep-chilled or crust-frozen in overwrapped trays by passing the package through a chill tunnel (40°C or lower) for approximately one hour. This process hardens the surface of the meat without freezing the interior and greatly extends the shelf- life of the product. USDA regulations require that poultry meat must remain above 26°F at the meat core to be labeled “fresh.” The typical fresh meat package for retail display is a foam tray overwrapped with a clear film. An absorbent pad is usually placed under the Figure 6.3 Chicken parts packaged in polystyrene tray with an oxygen permeable overwrap film.
Figure 6.4 Turkey drum portions packaged at the retail store in a polystyrene tray with an overwrap film.
meat to absorb purge. The pad is comprised of an absorbent material such as cellulose, sur- rounded with a porous, non-absorbent “plastic.” The overwrap film has a relatively high degree of oxygen permeability to allow the raw meat pigment to “bloom.” Fresh meat packaging overwrap materials are stretch PVC or stretch-shrink PE, with the trays made from EPS.
Raw poultry meat is highly perishable even when stored under chilled conditions. The growth of psychrotrophic spoilage bacteria is most often the cause of spoilage. While other factors will limit the shelf life of the poultry meat (especially initial bacterial levels), vacuum or modified atmosphere packaging can extend it. Generally, when vacuum or CO2 atmosphere is combined with chill temperatures, a significant increase in shelf life can be obtained. Furthermore, increasing the CO2levels to 80 and 100% can reduce the growth rate of spoilage bacteria on chicken compared to 20% CO2and vacuum packaging.
There are generally three methods used to vacuum-package poultry meat, depending upon the type of meat:
1. Whole carcasses are packaged in heat-shrinkable plastic bags with low oxygen per- meability, using a rotomatic or chamber with a clip seal or heat-seal system. 2. Cut-up poultry uses a vacuum system prior to heat-sealing the package.
3. Ground poultry uses a thermoforming or horizontal overwrap machine where the meat is placed in a tray, a vacuum is pulled, then the package is gas-flushed before being sealed.
Ground poultry meat requires different packaging due to color stability. Ground turkey breast meat is a popular product and is sometimes mixed with ground turkey thigh meat. Ground chicken thigh meat has a less stable color, so there is currently less on the market. All of these ground products are packaged in high oxygen atmospheres of 70 to 90%, usu- ally in PS foam trays with an overwrap film or lid stock that is a barrier to oxygen (Figure 6.6). The package headspace is usually held at a gas volume to meat/volume ratio of 1:1 or greater.
Retail package
MASTER PACKAGE
Contains CO2 or N2 gas
Research
Film permeability
Film permeability has been found to affect the growth of bacteria on fresh poultry. Generally, the reduction in the presence of oxygen in the package inhibits growth of the typical spoilage organisms associated with fresh poultry meat. Shrimpton and Barnes4 evaluated chilled poultry packaged in high and low oxygen permeable films testing PE, PVC/PVdC copolymer, and a modified PE. The high oxygen permeable copolymer delayed the detection of off odors and resulted in a higher concentration of oxygen in the package headspace compared to the other films evaluated. Fluorescent pigment produc- tion, lipolytic activity, and proteolytic activity of chicken spoilage bacteria were directly related to the availability of oxygen due to the packaging procedures.5The bacterial num- bers paralleled the increases measured in biochemical activities. In addition, fresh poultry meat packages must maintain constant moisture content within the package in order to maintain product quality as well as restrict bacterial growth.6The use of films with various oxygen permeabilities will affect the growth of bacteria and the color and odor of refrige- rated poultry meat.7Generally, low OTR films will retard bacterial growth while high OTR films will lower the off odor impact upon opening the package (Figure 6.7).
Vacuum and Modified Atmosphere Packaging (MAP)
Vacuum and modified atmosphere packaging (MAP) has been used to extend the shelf-life of packaged meat for several decades. Several MAP packaging systems for fresh poultry meat exist including: flexible trays with vacuum or gas-flush, rigid trays with lid stock and gas flush, heat-sealable bags with vacuum or gas flush, and master/bulk packaging over- wrap for vacuuming or gas flush multiple packages.8Carbon dioxide content is critical in MAP to control the growth of aerobic spoilage bacteria. Haines9was the first to show an inhibitory effect of CO2on aerobic spoilage bacteria. Barnes et al.10 found that vacuum- packaged, chill-stored poultry lead to the growth of mainly lactic acid bacteria and, in some cases, cold-tolerant coliforms. The use of CO2-enriched atmospheres for chilled poultry is based on the early work of Ogilvy and Ayres.11They found that the ratio of poultry meat shelf life in CO2to the shelf life in air could be expressed as a linear function with CO2con- centration. The CO2affected both the lag growth phase and generation time of the bacteria present. A minimum concentration of 20% in the package headspace is required to see a sig- nificant improvement in shelf life.12, 13The growth of pathogens on fresh chicken was inhib- ited by increasing the concentration of CO2with storage at 1.1°C, however, the lactic acid bacteria present were not inhibited, due to their facultative anaerobic abilities.14Thomson15 also found that a high CO2atmosphere inhibited the growth of bacteria on poultry com- pared to chicken packaged with ambient air. Fresh ground or skinless poultry meat is pack- aged in high oxygen atmosphere (70 to 80%) with the balance of atmosphere being CO2to Figure 6.6 Ground chicken and turkey packaged in a high oxygen modified atmosphere in poly- styrene trays with a barrier film overwrap.
maintain color yet limit the growth of spoilage bacteria. A refrigerated shelf life of 14 days is attainable using this system,8and slightly longer if accompanied by deep chilling. For retail packages, the CO2concentration should be limited to 35% to minimize package col- lapse and excessive purge. Nitrogen is often used as a filler gas, which minimizes purge without the addition of oxygen.