Shelf life can be defined by several factors including safety, microbial spoilage and quality deterioration. Quality deterioration can be related to off-flavor development often associated with lipid oxidation and discoloration can occur in raw meat with pigment oxidation or with cured color fading with cured meats, explains Gary Sullivan, assistant professor of meat processing for the University of Nebraska-Lincoln.

“Providing safety is essential for all products, and the shelf-life and quality characteristics must achieve the desired specifications for the product you are producing,” he says.

Many companies seem to be comfortable with the current shelf-life properties of their processed products, says Jim Dickson, a professor in the Department of Animal Science at Iowa State University in Ames. Most shelf-life extenders are antimicrobials, and the main driving force in processed meats is the control of Listeria monocytogenes, he adds.

While many shelf-life extending ingredients are applied as ingredients in the formulation, others are sprays or dips applied post-lethality. Work has been done to incorporate some into casings for use in comminuted products as well, Dickson says. Shelf-life extending ingredients that are growing include anything perceived as natural or clean label, such as vinegar or cultured sugar products, he says.

Shifting to natural

When looking at shelf-life extending ingredients used for meat processing, many ingredients provide multiple functions. For example, sodium nitrite provides cured meat color, flavor and aroma, but also reduces lipid oxidation and can slow or inhibit the growth of some pathogens and spoilage microorganisms, Sullivan explains. In addition, sodium erythorbate is used as a reducing compound, which increases the rate and effectiveness of sodium nitrite in cured meats. Salt also increases water retention, yield, provides protein extraction and can slow microbial spoilage. In addition, sodium phosphates work with salt to increase yield, water retention and protein extraction in part by dissociating the actomyosin bonds, but also can function as an antioxidant compound by chelating metals in meat products. Organic acid salts, such as lactates, diacetates, propionates and benzoates, also are used as antimicrobial ingredients for pathogen control of Listeria monocytogenes and Clostridium perfringens, but some organic acid salts can reduce microbial spoilage rates as well. Lactates also can delay discoloration in raw products injected with a lactate containing solution.

But these multifunctional shelf-life extending ingredients are among those that are being targeted to be removed and replaced with natural and clean-label ingredients.

“Often one or more ingredients are added to replace the functional properties of the ingredient being removed,” Sullivan says. “The combination of ingredients can provide additive and synergistic effects or a hurdle method to replace the control provided by the traditional ingredient being replaced.”

For example, sodium nitrite is being replaced with cultured celery juice powder, where bacteria have reduced nitrate to nitrite, as a natural nitrite source and acerola cherry powder is used as a natural source of ascorbic acid in production of alternatively cured meat products. “Some of these products are formulated with less ingoing nitrite than the regulatory limits of sodium nitrite,” Sullivan adds. “With less ingoing nitrite, additional methods to control pathogens and spoilage microorganisms in these products may be needed.”

The use of organic acid salts, with the combination of lactate and diacetate being the most common, are effective at controlling pathogens and provide the added benefit of reducing microbial spoilage. Some of the ingredients used to replace these include ferments such as cultured sugars, buffered vinegar products and lemon juice/citrus-based products, Sullivan says. “These may be used individually or in combination to provide pathogen control and reduced microbial spoilage rates,” he says. “Much research has been conducted on other natural antimicrobials from various fruits, vegetables and spices, but their effectiveness and application in the meat products have been limited.” 

As an alternative to added ingredients, high-pressure processing (HPP) can be used as an effective tool to reduce pathogens and spoilage

“The pressures and holding times will impact the extent of microbial reduction,” Sullivan explains. “HPP is most often applied to cooked processed meat products where the proteins have been stabilized [or set] during thermal processing. If HPP is applied to raw red meat products, it can lighten the color resulting in products losing some of its raw appearance and can increase lipid oxidation.”

Additional research in extending shelf life has included the use of bacteriophage, peptides (bacterial or animal sourced) and plant-based compounds/extracts, such as fruits, spices and herbs. From a shelf-life standpoint, the antioxidant function of sodium phosphates and from other synthetic antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene  (BHT), propyl gallate (PG) and tertiary butylhydroquinone (THBQ), is being replaced with various plant extracts including but not limited to rosemary, green tea and cherry along with lemon and other citrus products that are high in phenolic compounds, reducing capacity, and/or ability to chelate metals.

“It is not uncommon to use a combination of different plant extracts to provide a synergistic effect as they have different modes of action and/or locations of function in the products,” Sullivan says.

In addition, Vitamin E can be included in animal diets to improve oxidative stability in meat products, he adds.  

Including these natural and clean label ingredients do not always provide an easy transition though, Sullivan cautions, and some are much simpler than others.

“It is easier when developing a new product using natural/clean label ingredients as you have a whole new set of product characteristics, expectations, flavor profiles and shelf life,” he says. “When reformulating an existing product, it can be challenging to substitute natural/clean label ingredients for traditional ingredients while maintaining the exact same flavor, texture and appearance as the existing formulation.”

Additionally, Sullivan says it is important to keep in mind it is not always a one ingredient direct placement for one ingredient. One example is when using many of the natural and clean label antimicrobials, it is advised to add the ingredient at the very end of processing to prevent damage to the proteins from acid in the products. The replacement of sodium nitrite and sodium erythorbate with cultured celery juice powder and cherry powder is a more straight-forward replacement as they provide a direct replacement, Sullivan says.

“These challenges can be increased when more than one traditional ingredient is being replaced by multiple natural/clean label ingredients,” he says. “Work in industry and academia continues to search for the next new antimicrobial and antioxidant compounds.”

Moving forward, Dickson also expects emphasis to continue to grow for natural and clean-label products as that is the direction consumers are going. He also expects to see classification of some processing aids, which do not require labeling.  NP