Food Packaging Technology 3(2+1)

Lesson- 17 Selection criteria of packaging material for raw foods

17.0 Raw Meat

The adoption of preservative packaging for raw meats has led to major changes in the processing and marketing of such products. As a result of the widespread adoption of vacuum packaging for primal cuts of red meats, trade in red meat carcasses has declined to trivial proportions in many developed countries, and the international trade in chilled raw meats has greatly increased, with a consequent decline in trading of frozen meats. The enhanced stability of vacuum-packaged products has facilitated consolidation of meat-packing facilities. 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. Fresh meat is vulnerable to microbiological deterioration from microorganisms. These microorganisms can be as benign as slime formers to stink producers to pathogens such as E. coli O157:H7. The major mechanisms to retard fresh meat spoilage are temperature reduction, often coupled with reduced oxygen during distribution, to retard normal spoilage microbial growth. 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 ultilayer flexible material pouches closed by heat scaling the end after filling.

17.1. Fish and Sea foods

Varieties of fish are among the most difficult of all foods to preserve in their fresh state because of their inherent microbiological populations many of which are psychrophilic, i.e., capable of growth at refrigerated temperatures. Further, seafood may harbor a nonproteolytic anaerobic pathogen, Clostridium botulinum type E, capable of toxin production without signaling spoilage.

The high-quality shelf life of most seafood in chill storage is relatively short, being only a few days. This short period does not allow sufficient time from reception through to distribution and display to ensure the restaurateur or consumer can obtain seafood at its best. 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.

17.2. Fruits and vegetables

Increasing demand for a wide range of harvested fruits or vegetables (raw and fresh-cut) has led to dynamic growth in sales and new market opportunities for the fresh produce sector. However, their preservation still constitutes one of the most challenging applications for the food industry. Fresh produce is a living, “breathing” entity fostering the physiological consumption of oxygen and production of carbon dioxide and water vapor. From a spoilage standpoint, fresh produce is more subject to physiological than to microbiological spoilage, and measures to extend the shelf life are designed to retard such reactions and water loss. One major problem is that produce may enter into respiratory anaerobiosis if the oxygen concentration is reduced to near extinction. In respiratory anaerobiosis, the pathways produce undesirable flavor compounds. To minimize the production of these undesirable end products, elaborate packaging systems have been and continue to be developed. Most of these involve mechanisms to permit air into the package to compensate for the oxygen consumed by the respiring produce. High gas permeability plastic films, micro perforated plastic films, plastic films disrupted with mineral fill, and films fabricated from temperature-sensitive polymers have all been proposed or used commercially.

Fresh-cut vegetables, especially lettuce, cabbage, and carrots have been a major product in both the retail and the hotel/restaurant/ institutional market. Cleaning, trimming and size reduction lead to greater surface to volume of the produce and to the expression of fluids from the interior to increase the respiration and microbiological growth rate. On the other hand, commercial fresh-cutting operations generally are far superior to mainstream fresh produce handling in cleanliness, speed through the operations, temperature reduction, and judicious application of microbicides such as chlorine. Uncut produce packaging is really a multitude of materials, structures, and forms that range from the old and traditional, such as wood crates, to inexpensive, such as injection-molded polypropylene baskets, to polyethylene liners within waxed corrugated fiberboard cases. Much of the packaging is designed to help retard moisture loss from the fresh produce or to resist the moisture evaporating or dripping from the produce (or, occasionally, its associated ice) to ensure the maintenance of the structure throughout distribution. Some packaging recognizes the issue of anaerobic respiration and incorporates deliberate openings to ensure passage of air into the package, as, for example, perforated polyethylene pouches for apples or potatoes.

For freezing, vegetables are cleaned, trimmed, cut, and blanched prior to freezing and then packaging, or prior to packaging and then freezing. Blanching and the other processing operations reduce the number of microorganisms. Produce may be individually quick frozen (IQF) using cold air or cryogenic liquids prior to packaging or frozen after packaging as in folding paperboard cartons. Frozen food packages are generally relatively simple monolayer polyethylene pouches or polyethylene-coated paperboard to retard moisture loss. Fresh-cut vegetables coupled with bread sticks and dip constitutes a reasonably flavorful mouthful and nutritious snack for adults and younger persons.

17.3. Milk

Milk is a complex mixture of water, proteins, lipids, carbohydrates, enzymes, vitamins, and minerals. Due to its specific composition and a pH close to neutral, it is a highly perishable product with high spoilage potential that can result in rapid deterioration of quality and safety. Packaging serves a number of different functions, including containment, protection, convenience, and communication, the most important being protection. Packaging protects milk and dairy products against environmental, physical, chemical, as well as mechanical hazards. It also protects the product from loss of desirable flavor compounds or pick-up of undesirable odors, and contamination from spoilage or pathogenic microorganisms, insects, or rodents during storage and distribution. An effective packaging system should fulfill numerous other requirements, including compatibility with the dairy product it contains recyclability or reuse, tamper evidence, nontoxicity, aesthetics, machinability, and functionality in terms of shape, size, and disposability.

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. In recent years, milk packaging has been upgraded to incorporate reclosure, a feature that has been missing from gable top polyethylene-coated paperboard cartons. Further, in recent years, the packaging environmental conditions have been upgraded microbiologically to enhance refrigerated shelf life. Aseptic packaging is employed to deliver ambient temperature shelf stable fluid dairy products. The most common processing technology is ultra high temperature short time thermal treatment to sterilize the product, followed by aseptic transfer into the packaging equipment. Fluid milk is generally pasteurized, cooled, and filled into bag-in-box pouches for refrigerated distribution.