Effect of Supermarket Display Case Lighting on Modified Atmosphere Packaging (MAP) Meat
The rates of oxidation and decomposition can be slowed by the use of barrier films and various gas combinations in modified atmosphere packaging (MAP), but radiation from retail lighting, especially UV radiation but also visible spectrum radiation, can still initiate oxidation and spoilage as all wavelengths of light penetrate clear packaging to some extent.
Wrapping fresh meat provides the opportunity to encase the meat in an atmosphere composed of a specific combination of gases, which allows retailers to control the timing of meat blooming and prolongs the storage life of the meat.
Modified atmospheres range from Controlled Atmosphere Packaging (CAP), which is 100% carbon dioxide and maintains the initial purple color of freshly slaughtered meat, to high oxygen Modified Atmosphere Packaging (MAP), which contains 70% oxygen and 30% carbon dioxide and is ideal for initiating meat blooming, the change in meat color from purple to bright red.
MAP with high oxygen concentrations helps to keep the red pigment stable within the muscle tissue for twice as long as meat exposed to air. In one study beef in high oxygen (70% oxygen and 30% carbon dioxide) modified atmosphere packaging remained fresh for four weeks at -1.5°C, and three weeks at 0°C.
In addition, the transparent film can allow a greenhouse effect to occur especially when high intensity spotlights are used, in which the radiation from the lamp heats the meat beneath the wrapping and the heat is then trapped there, causing the moisture within the meat to evaporate and then condense on the inside of the package.
As meat case lighting penetrates the transparent meat wrapping surrounding the modified atmosphere, a greenhouse effect develops in which the meat absorbs ultraviolet and harmful yellow wavelength radiation as heat which cannot escape from the polyvinyl packaging and is then trapped next to the surface of the meat. This heat can cause moisture within the meat tissue to evaporate and then condense on the inside of the wrapping as it too is trapped. This provides an ideal environment for the growth of bacteria, which accelerates the discoloration and decomposition processes, and for the growth of food borne pathogens such as Listeria and Salmonella. A temperature increase of only a degree or two can cause fresh meat to spoil at much faster rates, reducing the shelf life of fresh meat displays.
However, even in modified atmosphere packaging, the lamps used in the meat display cases can have a tremendous impact on the shelf life of beef, poultry, pork, and lamb. Exposure to light causes myoglobin to oxidize to metmyoglobin, a chemical reaction that causes fresh meat to lose its bright red bloom and become brown. In a study conducted at the University of Zaragoza, beef steaks in modified atmospheres of 70% oxygen, 20% carbon dioxide, and 10% nitrogen were exposed to three types of light, with a control sample kept in darkness. Beef steaks displayed under regular fluorescent lamps quickly absorbed the ultraviolet light emitted by the lamps, causing the steaks to turn brown and decompose as bacteria multiplied exponentially on the surface of the steaks. In contrast, steaks displayed under low UV Promolux lamps, and those under regular lamps blocked by Promolux filters, maintained virtually the same freshness and bright red color over the 28 days of the study as the beef stored in the dark. Exposure to ultraviolet light is therefore a much stronger factor than MAP in maintaining meat freshness and meat bloom.