Commercial food manufacturing is always searching for low-cost ways to reduce waste and increase profitability. Many today have heard the foodservice industry mnemonic device “FAT TOM” referencing the six favorable conditions required for the growth of foodborne pathogens: food, acidity, time, temperature, oxygen, and moisture. Vacuum packaging of food evolved from an attempt by food manufacturers to reduce or eliminate one of those conditions: oxygen.
Vacuum packaging should not be confused with shrink wrapping. Although both use a sealing bar and polymer film, they differ in two important ways. During the shrink-wrap process, products are enclosed in film and heat is applied to shrink the polymer, creating a form-fitting poly-enclosure. Air escapes the shrink-wrapped package through tiny vent holes along the film surface; because the packaging is not airtight, aerobic microorganism growth is not prevented. While this method is used for food products that require off-gassing, it does pose potential exposure to exterior elements.
Vacuum packaging does not use perforated polymer films, rather oxygen is removed from the food environment inside the packaging with suction. The product is then completely sealed off from exterior elements to modify the atmosphere in the package and extend the life of the product. Thus, vacuum packaging is used to protect food from the growth of harmful microrganisms during storage and distribution. It reduces the amount of air from a package and hermetically seals it so that a near-perfect vacuum remains inside. A common variation of the process is vacuum skin packaging (VSP), a process in which a flexible thermo-plastic barrier molds itself to the contours of the food being packaged when heat is applied. Although VSP sounds similar to shrink wrapping, the material used for the process is impervious to air, providing a hermetic seal. Both methods extend shelf-life without requiring heat or federally regulated chemical food additives for pathogen reduction.
Vacuum packaging can create a significantly anaerobic environment that prevents the growth of aerobic spoilage organisms or bacteria such as mold, aerobic yeasts, and pseudomonads. These organisms are responsible for the signs of spoilage, including off odors, slime, and texture changes.
Reducing the oxygen in and around a food helps prevent shrinkage or oxidative processes/water loss of the food and slows the amount of oxidative rancidity in fats and oils. Reduced-oxygen packaging (ROP) also prevents color deterioration in raw meats caused by oxygen. Additional benefits of vacuum packaging are: no or low risk of post-pasteurization contamination, ease of handling (flexibility reduces potential for damage to finished products and allows for a variety of sealing methods, including heat), inhibition of aerobic spoilage organisms, transparency, and chemical resistance.
Other ROP packaging processes include cook-chill, controlled atmosphere packaging (CAP), modified atmosphere packaging (MAP), and sous vide. ROP allows an extended shelf-life for vacuum packaged, MAP, and CAP foods displayed for retail sale. Food processed through cook-chill or sous vide cannot be sold directly to consumers or to other businesses, but provide extended shelf-life and quality benefits for foodservice. Because of the potential weaknesses of these packaging methods (alone) to manage known pathogenic hazards, they are controlled by government regulation.
Economic and quality advantages of these include extended shelf-life for ready-to-eat convenience foods and the ability to be advertised as “Fresh — Never Frozen.”
Not all pathogens require air for survival or growth. Clostridium botulinum, the most persistent known spore-forming foodborne pathogen, is a pathogen which is provided a suitable growth environment in the absence of oxygen, although it cannot multiply in an oxygen-rich environment. Vacuum-packaged foods that have not undergone a strict thermal process to destroy C. botulinum spores are susceptible to those spores persisting and thriving. Refrigerated storage is required throughout the product’s shelf-life to inhibit pathogen growth, though there are C. botulinum strains which can grow to toxic levels even when refrigerated.
Processors of products using vacuum packaging or other reduced-oxygen packaging are required by federal and international regulations to build in extra safeguards if they plan to rely on refrigeration as the sole (supporting) barrier to ensure product safety. If extended shelf-life is sought, a temperature of 38°F or lower must be maintained to prevent growth of C. botulinum and the subsequent production of toxin. Listeria monocytogenes can grow at even lower temperatures, so appropriate use-by dates must be established.
If longer shelf-life is needed, manufacturers are required to apply additional measures or growth barriers to prevent bacteria growth or toxin formation. These measures include heat treatment, acidification, salt level increase to 3.5% or higher in the water phase, reduced water activity to 0.97 or lower, or preservative addition (e.g., nitrites). Any one hurdle, or a combination of several, may be used with refrigeration to control pathogenic outgrowth.