Preserving color

by Donna Berry
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Processors must never forget that the color of meat influences consumer purchasing decisions.
Processors must never forget that the color of meat influences consumer purchasing decisions.

Consumers often perceive hand-prepared and packaged sandwiches, salads, wraps and other meals as being fresher, simpler, less processed, or even homemade. The truth is, just like most commercially prepared and packaged foods, commissary-produced foods rely on preservation systems to ensure product integrity and safety through shelf life.

First and foremost, it is necessary that meats used to build sandwiches or are included in packaged salads maintain color appeal, as humans are visually oriented. They eat with their eyes.

“What we see directly impacts our expectations about the taste of that product,” says Herbert Stone, spokesperson and past president for the Institute of Food Technologists in Chicago, and an authority on sensory science. “When consumers shop, their choices are impacted by how the product appears.”

Faded roast beef, grayish ham and pink grilled chicken do not sell. These discolorations can occur as a result of surface myoglobin oxidation and result in product discard even though they are safe to eat.

“Fortunately, the color of meat can be controlled,” says Jane Boles, associate professor of meat science at Montana State Univ., Bozeman, Mont. This control comes in the form of proper handling, preparation, packaging and added ingredients.

“Myoglobin is a water-soluble protein that contains iron, with the state of the iron atom influencing meat color,” Boles says. “During the cooking process, myoglobin is denatured, resulting in the brownish color easily recognized in cooked meat products.”

In some ready-to-eat (RTE) meats, such as sliced roast beef, the myoglobin is not completely denatured. Care must be taken to prevent oxidation, as the consumer expects some red.

With cured meats such as ham, added nitrites assist with color development. These are either added directly via curing salts or indirectly through “natural” ingredients such as celery powder, which contain inherent high concentrations.

When nitrite meets water, it forms nitrous acid and nitric oxide. “In meat, these compounds combine with the protein myoglobin to form nitric oxide myoglobin,” Boles says. “This pigment is not stable until after cooking when the final cured pigment, nitrosylhemochrome, is formed. The cooked pigment is more stable, but is still sensitive to oxygen, temperature and light. This is why most cured products are vacuum packaged.

“Many problems can occur in the curing of meat products that can result in the development of strange colors,” Boles says. “One of the most common is the oxidation of the pigment to form a green or gray color.” This can be caused by metal contamination, such as that encountered in slicers and knives containing copper or iron.

Sometimes pink color forms in uncured cooked meat products. For example, cooked beef can become contaminated with nitrite by contact with a cured product, incomplete cleaning of utensils used with cured products or water contaminated with nitrites. This contamination can develop cured meat color on cooked beef.

“A pink color can also be formed in slow-cooked meat products that have not been contaminated with nitrite,” Boles says. “It is caused by specific conditions that promote interaction of natural meat pigments and nitrogen containing constituents of meat.”

Such surface pinking, also termed “pink ring,” can occur if gas ovens or barbecue grills are used to cook meat products. “Incomplete burning of the gas or contaminates in the gas result in the formation of nitrogen dioxide and nitric oxide, with the latter producing a pink color,” Boles says.

Iridescence is another type of color defect, one quite common in sliced roast beef and ham products. “The dominant color is frequently green and consumers sometimes confuse this with green myoglobin pigments associated with microbial growth,” Boles says. “Iridescence is produced by a combination of the angle of incidence of light on the muscle fibers and the wetness of the surface. If the fibers are pulled slightly out of alignment during slicing, the light strikes at an angle that scatters the light, having it appear as a rainbow or greenish color on the surface of the meat.” This off color can also develop after the meat is exposed to the metal on a knife or slicer, with the iron content of the meat undergoing a chemical change that alters the pigmentation.

Understanding Antioxidants

Consumers' choices are impacted by how the product appears.
Consumers' choices are impacted by how the product appears.

Flavor and aroma changes can also occur as a result of oxidation. This time it’s with the fat either inherent to the RTE meat or introduced via a condiment or marinade, not the myoglobin. When not properly stabilized, autoxidation of fat occurs, which produces a stale, old, rancid taste and smell. Again, the food is perfectly safe to eat, but not so delicious anymore.

“Packaging materials – and ingredients with antioxidant properties – are designed to slow the rate of oxidation and thus extend the product’s appeal,” Stone says.

Most RTE meat processors rely on some form of vacuum packaging to assist with retarding oxidation. In addition, suppliers offer a number of ingredients known as antioxidants that also assist.

Traditional synthetic antioxidants are chemically derived. Their names give them away: ethylene diamine tetra acetic acid (EDTA), tertiary butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT).

With today’s consumers increasingly reading food labels and often rejecting products containing ingredients that sound like they were concocted in a lab, processors are embracing clean-label antioxidants that can be discreetly added to product formulations.

For example, rosemary extract is a concentrated source of phenolic compounds, in particular carnosic acid, which has been shown to retard oxidative rancidity in meat, as well as function as an antimicrobial. Advanced technologies are used to remove or reduce the rosemary taste, yet the ingredient is labeled as rosemary extract or natural flavor.

It is often used alone or in combination with green tea extract, which is a concentrated source of the antioxidants classified as catechins, half of which are the highly effective epigallocatechin gallate. Green tea extract also contains an array of other chemicals that work together synergistically to slow oxidation.

A newer entry is acerola cherry extract. It is proving to be a highly effective ingredient in delaying both lipid and myoglobin oxidation, thereby delaying the onset of color loss and maintaining the desirable color and quality of meat products.

Another popular oxygen scavenger is vitamin E. Specifically, vitamin E classified as mixed tocopherols is best recognized for its ability to prevent lipid oxidation in meat.

Operators of RTE meal preparation facilities must never forget that the color of meat products influences consumer buying decisions. Color affects their perception of the freshness of the product. Knowing the factors that affect color and the best practices and ingredients that can prevent discoloration must be factored into meat sourcing and commissary procedures.

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