Lesson- 29 Performance evaluation of packaging on meat products and dairy products
It has become increasingly important to integrate packaging into the total product system if the objectives of delivering safe and high quality food are to be achieved.
Most meat is offered to consumers in a freshly or recently cut form, with little further processing to suppress the normal microbiological flora present from the contamination received during the killing and breaking operations required to reduce carcass meat to edible cuts. Reduced oxygen also leads to fresh meat color being the purple of myoglobin, a condition changed upon exposure to air which converts the natural meat pigment to bright cherry red oxymyoglobin characteristic of most fresh meat offered to and accepted by consumers. Reduced oxygen packaging is achieved through mechanical removal of air from the interiors of gas barrier multilayer flexible material pouches closed by heat scaling the end after filling.
About 40% of fresh beef is offered in ground form to enable the preparation of hamburger sandwiches and related foods. Ground beef was originally a byproduct, that is, the trimmings from reducing muscle to edible portion size. The demand for ground beef is so great that some muscle cuts are specifically ground to meet the demand. The most common packaging technique is pressure stuffing into chubs which are tubes of flexible gas barrier materials closed at each end by metal clips. At retail level the coarsely ground beef is finely ground to restore the desirable red color and to provide the consumer with the desired product.
The retail cuts and portions are placed in expanded polystyrene (EPS) trays which are overwrapped with plasticized polyvinyl chloride (PVC) film. The tray materials are fat and moisture resistant only to the extent that many trays are internally lined with absorbent pads to absorb the purge from the meat as it ages and/or deteriorates in the retail packages. The PVC materials are not sealed but rather tacked so that the modest water vapor barrier structure does not permit loss of moisture during distribution.
29.1.3 Case-Ready Meat
Case-ready retail packaging involves the cutting and packaging under hygienic conditions to reduce the probability of microbiological contamination. The package is usually in a gas barrier structure, typically gas/moisture barrier expanded polystyrene trays heat seal closed with polyester/gas barrier film. The internal gas is altered to a high oxygen/high carbon dioxide internal atmosphere. The high oxygen concentration fosters the retention of the consumer desired red color while the elevated carbon dioxide suppresses the growth of most spoilage microorganisms. for ease-ready beef and pork include the master bag system used widely for cut poultry in which retail cuts are placed in printed polyolefin film overwrapped EPS trays and the trays are multipacked in gas barrier pouches whose internal atmospheres are carbon dioxide to retard the growth of aerobic spoilage microorganisms.
29.1.4 Processed Meat
Longer-term preservation of meats is achieved by curing using agents such as salt, sodium nitrite, sugar, seasonings, spices, and smoke, and processing methods such as cooking and drying to alter the water activity, add antimicrobials, provide a more stable red color, and generally enhance the flavor and mouth-feel of the cured meats. Frankfurters are generally packaged in twin web vacuum packages in which the base tray is an in-line thermoformed nylon/polyvinylidene chloride (PVDC) web and the closure is a heat-sealed polyester (PET)/PVDC flexible material. Sliced luncheon meats and their analogs are in thermoformed Unplasticised PVC or polyacrylonitrile (PAN) trays heat-seal closed with PET/PVDC film. Sliced bacon packaging employs one of several variations of PVDC skin packaging (in contact with the surface of the product) to achieve the oxygen barrier.
Poultry is largely chicken, but turkey has become a much more significant category of protein. The dressed birds are chilled in water close to their freezing points after which they are usually cut into retail parts and packaged in case-ready form: expanded polystyrene trays overwrapped with printed PVC or polyethylene film. All meat products may be preserved by thermal sterilization in metal cans. Product is inserted and the container is hermetically sealed usually by double seam metal end closure. After sealing, the cans are retorted to destroy all microorganisms present and cooled to arrest further cooking. The metal serves as a gas, moisture, microbial, etc., barrier to ensure indefinite microbiological preservation.
29.1.6 Sea Foods
Packaging for fresh seafood is generally moisture resistant but not necessarily against microbial contamination. Simple polyethylene film is employed often as a liner in corrugated fiberboard cases. The polyethylene serves not only to retain product moisture but also to protect the structural case against internal moisture. Seafood may be frozen in which case the packaging is usually a form of moisture resistant material plus structure such as polyethylene pouches or polyethylene coated paperboard cartons. Canning of seafood is much like that for meats because all sea foods are low acid and so require high pressure cooking or retorting to effect sterility in hermetically sealed metal cans.
29.2 Dairy Products
Milk and its derivatives are generally excellent microbiological growth substrates and therefore potential sources for pathogens. For this reason, almost all milk is thermally pasteurized or heated short of sterility as an integral element of processing. Refrigerated distribution is generally dictated for all products that are pasteurized, to minimize the probability of spoilage. Milk is generally pasteurized and packaged in relatively simple polyethylene- coated paperboard gable top cartons or extrusion blow-molded polyethylene bottles for refrigerated short-term (several days to 2 weeks) distribution. Three general types of aseptic packaging equipment are employed commercially: vertical form / fill/seal, in which the paperboard composite material is sterilized by hydrogen peroxide, erected preformed paperboard composite cartons that are sterilized by hydrogen peroxide spray, and bag-in-box in which the plastic pouch is presterilized by ionizing radiation. The former two are generally employed for consumer sizes while the last is applied to hotel/restaurant/institutional sizes, largely for ice cream mixes. Fluid milk is generally pasteurized, cooled, and filled into bag-in-box pouches for refrigerated distribution.
Fresh cheeses such as cottage cheese, fabricated from pasteurized milk, are generally packaged in polystyrene or polypropylene tubs or polyethylene pouches for refrigerated distribution. These package forms do not afford significant protection beyond barrier against recontamination, i.e., they are little more than rudimentary moisture loss and dust protectors because the refrigerated distribution time is so short.
29.2.3 Fermented Milks
Fermented milks such as yogurts fall into the category of fresh cheeses from a packaging perspective, i.e., they are packaged in either polystyrene or polypropylene cups or tubs to contain and to protect minimally against moisture loss and microbial recontamination. Aseptic packaging of such desserts is occasionally performed to achieve extended ambient temperature shelf life. Two basic systems are employed, one with preformed cups and the other, thermoform/fill/seal. In cured cheese, microbiological growths may be retarded by packaging under reduced oxygen and/or elevated carbon dioxide. Commercially, gas barrier packaging is used to retain the internal environmental condition. Generally, flexible barrier materials such as nylon plus polyvinylidene chloride or polyester/polyvinylidene chloride are employed.
29.2.4 Ice Cream
Ice cream and related frozen desserts are distributed under frozen conditions. The product must be pasteurized prior to freezing and packaging. The packaging is basically moisture resistant because of the presence of liquid water prior to freezing and sometimes during removal for consumption. Water-resistant paperboard, polyethylene-coated paperboard, and polyethylene structures are usually sufficient for containment of frozen desserts.