Meaty Solutions for Shelf Life

Consumers have myriad choices when buying meat, including raw, precooked and frozen. Behind the scenes, each product has unique requirements that ensure safety and quality throughout its shelf life.

Feared factors

Microorganisms can cause illness and also contribute to spoilage by creating off odors, slime, color and flavor change. You get different types of spoilage bacteria depending on how the product is packaged. For a meat product under anaerobic conditions, you get primarily lactic-acid bacteria, says Michael Doyle, Ph.D., director of food safety and quality enhancement, University of Georgia, Athens. Under aerobic conditions where you have oxygen present, you get organisms like Pseudomonas.

Oxidative rancidity also impacts meat palatability. Oxidized fat has a rancid flavor, and fat that has oxidized during refrigeration after the meat has been cooked has a warmed-over flavor.

Debugging meat

Nitrates in cured meats form their characteristic color and flavor, but also prevent Clostridium botulinum growth in dried sausages. Salt in cured meats also controls microorganism growth by creating osmotic pressure that dehydrates cells. Sugar acts as a food source for Lactobacillus, which in turn reduces the pH, creating a tangy flavor and inhibiting other microorganisms.

Smoke also adds flavor and inhibits oxidation and bacteria growth. A natural smoke ingredient with bactericidal capabilities can replace sodium lactate and sodium diacetate in hot dogs and possibly other meats. Weve been able to isolate the component in natural smoke to move from a bacteriostatic effect to a bacteriocidal effect, says Paul Hood, Zesti-Smoke® business manager, Mastertaste, Monterey, TN. He notes that the ingredient helps achieve USDA-required kill levels for Listeria and also extends shelf life. It is typically labeled as natural flavor or natural smoke flavor.

The criteria for selecting antimicrobials include regulations, meat species, formulation, processing, packaging, distribution and storage, according to David Charest, director of food protection, North America, Danisco USA, Inc., New Century, KS. For example, if a customer is interested in a kill step or controlling the outgrowth of Listeria monocytogenes, a number of organic-acid-based solutions or equipment-based solutions are available. If a customer is interested in a kill step and outgrowth control, the selection of ingredients is more limited to products like NovaGARD LM blends, which kill and control Listeria, he says.

Many antimicrobials for meat are based on acids and their salts. Lactates extend product shelf life by inhibiting spoilage and pathogenic bacteria. Sodium and potassium lactate can be added directly to meat at a maximum level of 4.8% lactate to comply with USDA regulations. On its website (www.purac.com), Purac, Lincolnshire, IL, says that salt in a formula may need to be reduced to compensate for sodium lactates salty flavor. Sodium diacetate can be used alone, and is synergistic with sodium or potassium lactate. Sodium diacetate has a maximum use level of 0.25% set by USDA, but is limited by flavor. Organic acids used as secondary additives in the form of a dip or spray include lactic, acetic and fumaric acids.

USDA approved lauric arginate for the antibiotic treatment of fresh and precooked meats. It can be applied topically as a dip or spray to protect the surface of ready-to-eat meats from L. monocytogenes. Lauric arginate is essentially a two-in-one system, whereas most other ingredients only offer one of the following benefitspost-pasteurization kill, or growth inhibition during shelf lifeit does both with one application, says Kiran Krishnan, regional sales manager, A&B Ingredients, Inc., Fairfield, NJ.

The application method depends upon product type and level of enhancement. Many organic acids are used as carcass washes. For the best distribution throughout the product, Charest recommends injection followed by tumbling. An ideal method of application is to add dry ingredients to the brine, which is then distributed within the matrix of the meat product, he says.

Cutting off oxygen

Chemically speaking, antioxidant is a general term that refers to compounds that interfere with the oxidation reaction. In foods, they can be divided into three classifications: natural extracts, phenolics or synthetic, and vitamin-based. Most antioxidants have at least one phenol group.

Natural extracts derived from herbs and spices that exhibit antioxidant properties include those from rosemary and oregano, as well as other plants. Fruit ingredients that contain high levels of naturally-occurring antioxidants include raisins, cranberries, cherries, dried plums, blueberries and grape seed. (See sidebar, Not Such a Fruity Idea, for more information on fruits in meat applications.) All of these ingredients are label-friendly, and often their flavor can help mask oxidized flavor, as well as prevent it.

Synthetic antioxidants include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquinone (TBHQ) and propyl gallate. These are used in minute amounts, on the order of parts per million. Title 9 of the Code of Federal Regulations, Sec. 424.21, gives the maximum usage of these ingredients.

Vitamin-based antioxidants include ascorbic acid, ascorbyl palmitate and tocopherols. Ascorbyl palmitate is less polar than ascorbic acid, and will dissolve in fats more readily. Erythorbic acid is a stereoisomer of ascorbic acid, used as an antioxidant in processed meats. Tocopherols have good process stability, and their ability to arrest oxidation carries through past heat treatment. The tocopherols generally used as antioxidants are mixed tocopherols, and those with the highest levels of delta and gamma tocopherols will have the highest antioxidant activity. EDTA (ethylenediaminetetraacetic acid) and citric acid are chelating agents that bind up metal ions that promote oxidation.

Antioxidants have different strengths and will vary in effectiveness according to the meat composition and handling. Selection criteria include legal status and labeling requirements (which vary from country to country), dispersion and application of the antioxidant, and carry-through beyond cooking. Some antioxidants are synergistic.

Atmospheric approaches

The mix of gases surrounding the meat can affect meat color, oxidation and the growth of spoilage organisms. A high-oxygen environment allows beef myoglobin to retain a cherry-red color. At retail, the shelf lifes limiting factor of fresh red meats, such as ground beef, is usually a rapid color deterioration, which results in loss of consumer appeal, says Christine Boisrobert, applications development manager, food science, Air Liquide Industrial U.S. LP, Houston.

High-oxygen environments accelerate oxidative rancidity, the growth of aerobic spoilage organisms and, in the case of cured meats, the rate of color deterioration. Therefore, low-oxygen environments extend shelf life. Boisrobert explains: While beef processors often choose highoxygen MAP for retail applications, they might consider the use of low-oxygen MAP, i.e., mixtures of nitrogen and carbon dioxide, for foodservice operations. Hotel, restaurant and institutional establishments will typically favor reduced lipid oxidation and a longer microbial shelf life over the preservation of meat color.

Frozen meat is also prone to oxidization, albeit more slowly than its refrigerated counterpart. We see the need for good oxygen barriers and packaging materials for long-hold frozen-meat products, says Mark Franzreb, director of new business development, Cryovac Food Packaging Division of Sealed Air Corporation, Duncan, SC. In many cases they do not use oxygen barriers, but you will see lipid oxidation develop over time in freezer storage.

Meat-packaging material should be a good oxygen barrier with a high moisture-vapor transmission rate, explains Franzreb. He does list a few exceptions: With fresh poultry you want something that is considered a non-barrier. In a barrier film or bag, poultry, particularly if it is bone-in with the skin on, will develop a very strong confinement odor within about five or six days. Another exception is fresh seafood. The FDA mandates a film permeability rate of at least 10,000 cc per square meter for the sale and distribution of fresh seafood, because of the potential issue of botulism growth within seafood packages, he says.

The carbon dioxide and the nitrogen with no oxygen increases the shelf life by reducing the rate of spoilage, Doyle says. It does two things. The anaerobic environment delays chemical spoilage that occurs when oxygen is present and results in lipid oxidation that makes meat smell and taste rancid. Theres also a change in the microbial spoilage bacteria as well.

Lactic acid bacteria largely grow in the carbon dioxide/nitrogen/ carbon monoxide treated package, whereas in the overwrap packages in which oxygen is present, pseudomonads grow as primary spoilage bacteria. The pseudomonads can produce major off odors and off flavors. The lactic acid bacteria generally do not produce offensive off odors and flavors like pseudomonads.

One concern about this technology is that even spoiled meat would look fresh. The processor should not put too long of a shelf life on these types of products, but rather should validate shelf lives with controlled studies, Doyle recommends. Secondly, temperature control of products throughout distribution and retail is important to retain the integrity of the expected shelf life.

One other promising technique involves packaging sensors. Food Quality Sensor International, Inc., Lexington, MA, developed freshQ, a smart label that senses spoilage in fresh meat and poultry products. This stick-on sensor label goes on the outside of fresh wrapped meat and poultry packages and detects foodborne bacteriological levels through the wrap. When the inside of the quality Q on the label appears orange, the product is fresh. When the bacteria count in the package builds to a critical level, the orange turns to grey to indicate spoilage.

As effective as MAP is, Boisrobert stresses that it works in concert with other preventive measures. One cannot emphasize enough that gases are not remedial but complementary to good sanitation practices and strict temperature control, she says. High-oxygen MAP cannot improve a poor quality product, nor can it protect from temperature abuse. Carbon dioxide is most effective when the initial bacterial load is low.

Karen grenus, Ph.D., has eight years combined experience in applied research and product development in the area of dry blends for savory applications. She holds a doctorate degree from Purdue University in Agricultural and biological Engineering. Meat-packaging material should be a good oxygen barrier with a high moisture-vapor transmission rate.

Not Such a Fruity Idea

There has been a lot of buzz about antioxidants and human health lately, but antioxidants in fruit can also help minimize oxidation in meat, fight rancidity and the resulting off-flavors, and help maintain color. Fruits contain antioxidant compounds such as quercetin, isoquercitrin, cinnamic acid, anthocyanins, flavonoids and proanthocyanidins. Plus, their citric, malic and ascorbic acids can sequester trace metals that promote oxidation.

In research supported by the California Dried Plum Board, Sacramento, CA, Jimmy T. Keeton, Ph.D., and his team at Texas A&M University, College Station, found that at 3%, dried plum puree is an effective antioxidant in preventing oxidative rancidityas effective as a combination of BHA (butylated hydroxyanisol) and BHT (butylated hydroxytoluene), which are standard chemical antioxidants used at 0.02%, says Keeton, for both refrigerated and frozen precooked pork sausage.

Sour cherry also exhibits antioxidant power comparable to that from BHA and BHT, according to a study (J Agric Food Chem, 1998; 46:4891-7). Secondary lipid oxidation products in raw patties containing cherry puree were reduced by up to 80% after nine days storage. For cooked patties, stored for four days, the amount of oxidation was reduced by almost 90%, compared to controls without cherry.

One study (J Muscle Foods, 2006; 17, 248-266) showed that various cranberry-powder components inhibit meat fat oxidation. Fractions enriched in phenolic acids, anthocyanins, flavonols and proanthocyanidins were tested. A high-flavonol version showed the greatest inhibitory effect on oxidation in cooked pork (81%), with the others ranging from 22% to 56%.

According to a report commissioned by the California Raisin Marketing Board, Fresno, CA, Evaluation of the Potential Anti-Microbial Properties of Raisins and Their Application in Food Safety and Preservation, by Mark A. Daeschel, Ph.D., Professor, Oregon State University, Corvallis: Our results suggest that raisins have antioxidant and antimicrobial properties that are related to their phenolic content. Even though much of the phenolics is lost because of browning reactions, the drying process, when making raisins, concentrates the remaining amount and make them significant on a per weight basis.

Whats more, some of the naturally occurring compounds in all these foods also knock down the microbial count. So although these natural ingredients might be a bit tricky to incorporate, in some applications they may bear fruit in keeping meats fresher.

Lynn A. Kuntz