Keeping Foods Fresh

Consumers like - no, love - the concept of fresh food. However, fresh and convenience foods don't always go together. While a number of ingredient and processing technologies can help foods stay fresher longer, they may not meet the government's idea of "fresh" as far as the label. But product designers draw on these to provide or enhance the fresh characteristics of products as long as they avoid the legal faux pax of mislabeling.

Codified since January 1993 in Title 21 of the Code of Federal Regulations (CFR), Section 101.95, the 11-year-old definition of "fresh" has its fans, but many more challengers. For the most part, food manufacturers using advanced technologies to keep foods fresh, per se, cannot actually label the foods as such, as the definition rigidly limits the term.

The FDA definition applies to all direct or implied references to foods on their labels, including use in a brand name and as a sensory modifier. In general, FDA says that the term "fresh," when used on labels in a manner that suggests or implies that the food is unprocessed, means that the food is in its raw state and has not been frozen or subjected to any form of thermal processing or any other form of preservation. This has four exceptions: the addition of approved waxes or coatings; the post-harvest use of approved pesticides; the application of a mild chlorine wash or mild acid wash on produce; and the treatment of raw foods with ionizing radiation, as specified in 21 CFR 179.26. The definition also states that the necessity of refrigeration does not preclude use of the term.

FDA further says that manufacturers can use "fresh" on labels if it does not suggest or imply that a food is unprocessed or unpreserved. Thus, the term can describe pasteurized milk because it does not imply that the food is unprocessed, and consumers understand that milk nearly always undergoes pasteurization. However, it cannot be applied to pasta sauce that has been pasteurized or that contains pasteurized ingredients, as this implies that the food is not processed or preserved.

The CFR also states that the terms "fresh frozen" and "frozen fresh," on the label or in labeling food, mean that the food was quickly frozen while still fresh. Blanching before freezing does not preclude use of the term.

Many in the food industry believe that codifying and enforcing the definition of "fresh" has strengthened consumers' confidence in the term, creating greater certainty in their minds and greater value to the industry. Others believe that the 1993 rule was short-term and only was created to remedy misuse at the time in the marketplace. These groups want FDA to reexamine the "fresh" definition to correct any inconsistencies and to consider accommodating new processing technologies. Some proposed approaches would require that the agency evaluate each food product on its own merit to determine whether the term "fresh" applies.

Because this requires financial and manual resources, it is unlikely that the current definition of "fresh" will be changing any time soon, as FDA is not equipped for such an evaluation process. So for now, manufacturers should put aside the idea of using the term on product labels if they choose to include most of the following process or ingredient technologies.

Of the freshness-enhancing nonthermal technologies, many consider irradiation to be the most effective approach to eliminating pathogens and spoilage microorganisms from the food supply. Not only does it make food safe and extend shelf life, it does so while maintaining the product's freshness and nutritional wholesomeness. Irradiated foods undergo no major chemical, physical or sensory changes.

Unfortunately, when many people see the word "irradiation," they associate it with radioactivity. Unlike the gamma rays of radiation, however, irradiation uses ionizing radiation, also referred to as electronic beams, to zap microorganisms.  

In general, irradiation exposes food, either prepackaged or in bulk, to controlled levels of ionizing radiation. This type of energy is similar to radio and television waves, microwaves and infrared radiation. However, ionizing radiation's high-energy output allows it to penetrate deeply into food, disrupting the genetic material of microorganisms, thus destroying them.

Scientific studies, including many long-term, multi-generation animal-feeding tests conducted during the past five decades, have fully established the safety of irradiated food. More than 40 countries throughout the world have approved the use of food irradiation, and numerous national and international food and health organizations and professional groups have recognized its usefulness. FDA has approved irradiation for beef, poultry, pork, eggs, fruits, vegetables, roots and tubers, grains and legumes, spices and other types of foods.

In anticipation of a greater need for irradiation, the Institute of Food Science and Engineering at Texas A&M, College Station, TX, is establishing the National Center for Electronic Beam Food Research through a $185,000 USDA grant. The center will focus on conducting research, training and outreach on the use of electricity as an energy source for irradiating foods. It will work in conjunction with the year-old Electron Beam Food Research Facility, the result of a 10-year, $10 million research contract between Texas A&M and SureBeam Corp., San Diego, CA.

This past year, USDA approved a first-of-its-kind food irradiator located inside a cold-storage space in Pennsylvania. The irradiator accommodates food manufacturers' standard packaging up to 24 in. thick, in any shape or size. The facility meets the requirements for maintaining the cold chain of the meat, poultry, fruit and vegetable, and spice industries. The 4.4-million-cu.-ft. storage facility is dedicated to meet the needs of food companies in the Northeast, says Jim Wood, president of CFC Logistics Inc., Hatfield, PA. "Having an irradiator located within a cold-storage/logistics operation provides a unique service opportunity to food companies in the Northeast that want to irradiate their food and perishable products to kill foodborne illnesses," he says.

Another increasingly popular nonthermal technology, high-pressure processing (HPP), breaks noncovalent bonds, which interrupts cell functions and inactivates pathogenic bacteria. It also reduces spoilage microorganisms, so foods stay fresher longer. The foods' taste, color, texture and nutrition remain unchanged. While current HPP products require refrigeration, ongoing research that combines controlled heat with greater pressure will lead to the next generation: shelf-stable items.

"Our goal is to make fresh foods safe, without compromising their integrity. That's what makes HPP products attractive to consumers, retailers and foodservice distributors," says Terry Anstine, marketing director, Avure Technologies Inc., Kent, WA. "With our systems, we have a commercial, effective and reliable process to create the pressure, up to 87,000 psi, that destroys harmful pathogens without using significant heat, adding chemicals or irradiating food."

Recent USDA Food Safety and Inspection Service (FSIS) regulations have increased requirements for control of Listeria monocytogenes in ready-to-eat meats, like sliced sandwich meats. Now, processors can choose HPP as a post-packaging lethality step, and qualify for a preferred testing alternative.

HPP has already proven to be quite helpful in the seafood industry. For example, some oyster-industry processors turn to HPP technology to keep oysters fresh and safe for consumers to eat. Raw oysters can carry Vibrio vulnificus. FDA estimates that 5% to 10% of shellfish are contaminated with this dangerous bacterium; consumption of improperly cooked or raw shellfish harvested from infected waters can transmit the pathogen to humans. California recently instituted a law requiring Gulf oysters sold in the summer months to undergo a post-harvest processing method such as HPP. Pressure at about 45,000 psi reduces the Vibrio bacteria to nondetectable levels, and causes the oyster shell to relax and "shuck" itself, which creates a financial benefit for the processor.

HPP is also commonly used in the manufacture of increasingly popular refrigerated fruit and vegetable items such as guacomole and salsa. With both of these south-of-the-border products, consumers' desire for fresh taste and longer shelf life have encouraged use and acceptance of HPP among key retailers and distributors. Now, consumers can purchase and enjoy new categories of products, including nonthermally processed fresh fruit smoothies and organic juices, ripe avocado halves, chopped specialty onions and applesauce. "A taste is usually all it takes to be sold on HPP," says Anstine.

Pulsed electric field (PEF) technology, another common nonthermal food-preservation technique, applies a short burst of high voltage through fluid foods placed or flowing between two electrodes. The treatment is conducted at ambient or refrigerated temperatures for microseconds, minimizing heat generation due to energy transfer. PEF allows foods to retain fresh-like physical, chemical and nutritional characteristics, and extends refrigerated shelf life.

Radio-frequency electric fields (RFEFs) make an attractive option in fruit and vegetable juices to conventional heat pasteurization, which destroys nutrients and flavors. USDA Agricultural Research Service (ARS) scientists have shown that RFEFs inactivate bacteria in apple juice without heating. When moderate heat accompanies RFEFs, the combined inactivation effect greatly increases compared to the effect of either process alone.

Processors can add an array of ingredients to foods to help keep them fresh. Some must be labeled as a preservative, while others simply look like they are part of the product formulation.

For example, when added as a noncharacterizing ingredient, dried plums show effective antimicrobial properties in meat applications. Daniel Y.C. Fung and other researchers at Kansas State University, Manhattan, KS, have investigated the antimicrobial effects of varying levels of dried-plum purée and fresh plum juice in uncooked ground beef inoculated with five strains of pathogens. After five days, data show that the samples containing 3% or more of either plum ingredient contained fewer pathogenic bacteria than the control. In fact, the plum-containing beef samples had lower total bacterial counts, indicating plum ingredients suppress all bacteria.

The raisin is another ingredient that manufacturers can add to foods without drawing attention to its preservative effects. Raisins possess antimicrobial properties, thanks to their phenolic content. Golden raisins show the highest concentration of phenolics, due to their lack of browning. Even though many of the phenolics in dark raisins disappear because of browning reactions, the raisin drying process concentrates the remaining phenolics, making them significant on a per-weight basis.

Throughout history people have used spices for food preservation. Certain spices contain phenolic compounds, which can delay the onset of oxidation, and thus prolong foods' freshness. These compounds help neutralize the oxidation reaction by contributing hydrogen ions from their hydroxyl groups to unstable free radicals formed during the initiation of oxidation. The phenolic compounds are transformed into free radicals; however, these are more stable than the initial free radicals involved in oxidation. Thus, rather than preventing oxidation, they slow its progression, naturally.

Rosemary is likely the most widely used spice for its antioxidative properties, but other spices, such as cinnamon, sage and thyme, also demonstrate similar benefits. Meat, poultry and fish applications usually use such spices for preservation, as their sensory profiles are complementary. However, any fat system where the spice flavor complements the foods' overall flavor profile can use them.

Some suppliers have identified extraction methods that remove many of the characterizing flavors and aromas from spice extracts, rendering them virtually taste-free at levels used for antioxidative purposes. These levels vary by ingredient and supplier.

"Our Guardian line of antioxidants is rosemary-based, so it can be claimed as 'natural flavor' on the label," explains Bob Coyne, manager, sales and marketing/culinary, Danisco USA, New Century, KS. "Rosemary is also an effective antimicrobial agent when used in combination with other ingredients.

Appropriate applications include dressings, sauces, meat products, any precooked items and pet food - most any foods that are in need of keeping a 'freshness' flavor."

Through the years, live cultures have been used to keep fermented foods fresh, and they do so without many consumers being aware of this role. The preservative effect of lactic-acid bacteria during the manufacture and storage of such foods was historically believed to result from the acidic conditions created during fermentation, which converts carbohydrates into organic acids.

However, researchers have discovered that the preservation process involves more than simply a drop in pH. In fact, they have found that lactic-acid bacteria produce and excrete a variety of inhibitory substances other than lactic and acetic acids, including ethanol, hydrogen peroxide, diacetyl, free fatty acids, benzoate, antibiotics and bacteriocins. In addition, some beneficial microorganisms inhibit pathogens' growth by utilizing the resources that pathogens need to survive and proliferate.

Hence, cultures are another "natural" way to keep some foods fresh for a longer period of time, without raising the concern of chemical-wary consumers. For example, nisin, a polypeptide produced from Lactococcus lactis bacteria, inhibits the growth of Clostridium botulinum. Natamycin, also known as pimaricin, an antifungal agent produced by Streptomyces natalensis, is effective against yeasts and molds, but not bacteria.

Suppliers manufacture purified forms of both compounds for a limited number of FDA-approved food applications, mostly in the cheese category. Other foods, particularly nonapproved dairy applications, can reap the bacteriocidal benefits of nisin through the addition of nisin-producing lactic-acid bacteria.

For example, fermented dairy products, such as buttermilk, yogurt and sour cream, manufactured with a lactic-acid bacteria capable of synthesizing nisin or another bacteriocin have their own built-in, all-natural freshness system. Using cultured, bacteriocin-rich foods as ingredients in other foods is another way to indirectly add bacteriocins into foods without declaring them on labels.

For those fortunate FDA-approved applications, ongoing research is making the addition of purified forms of these ingredients more effective in keeping foods fresh. For example, researchers Joseph Marcy and John Koontz at Virginia Polytechnic Institute and State University in Blacksburg, VA, through funding by Dairy Management Inc.(tm), Rosemont, IL, are investigating methods to retard mold growth on the surface of cheeses with natamycin. The antifungal is approved for use on shredded cheese, which has a great deal of surface area, making it especially prone to mold.

Early in their research, Marcy and Koontz pinpointed and are successfully addressing two potential challenges, which are based on the fact that natamycin is practically insoluble in water and its stability is degraded during the ripening and storage of cheese, making it difficult to apply to cheese surfaces.

In its original form, natamycin is a dry powder that must be mixed in an aqueous liquid to form a supension that can be applied to food products. The problem starts during the application process, where natamycin suspensions can clog spray nozzles and prevent a uniform distribution of the bacteriocin onto the cheese surface. Once the spraying hurdle is overcome, another challenge arises.

"In terms of stability, natamycin is extremely sensitive to ultraviolet (UV) light," says Marcy. "Cheese products are exposed to high-intensity fluorescent lighting in the retail dairy case, resulting in natamycin degradation on the cheese by the time of purchase by consumers."

This degradation has traditionally rendered natamycin ineffective in prolonging the freshness of shredded cheeses. Marcy and Koontz's efforts to increase the water solubility and chemical stability of the antifungal have changed this. They formed molecular inclusion complexes of natamycin with cyclodextrins to increase solubility and chemical stability. "In these inclusion complexes, we found that more than 90% natamycin remained in the aqueous solution and it was significantly more stable than free natamycin," Marcy explains. "When addressing the issue of stability, we found that product packaging helped to greatly reduce natamycin photodegradation."

Indeed, proper packaging, along with process and ingredients, are essential to keeping food fresh. Barrier packaging is often combined with an antimicrobial gas flush. This system approach, referred to as modified atmosphere packaging (MAP), creates an environment that reduces or prevents spoilage by microbial growth.

The most frequently used gas is carbon dioxide, which is odorless and colorless and inhibits a variety of microorganisms. Effectiveness depends on variables such as gas concentration, initial contamination, water activity of the food and packaging barriers.

Researchers at Cornell University, Ithaca, NY, have identified a way of adding carbon dioxide to various dairy products, including cottage cheese and ice-cream mix. They believe that carbon dioxide penetrates microbial cell membranes, interfering with cytoplasmic enzymes and influencing cellular metabolism. The gas extends the lag phase of microbial growth, decreasing the growth rate. Since carbon dioxide is more soluble in water than oxygen, it displaces oxygen, and may minimize degradation reactions such as rancidity. Combined with high-barrier packaging, carbon dioxide can extend the shelf life of certain dairy products, keeping them fresh for a longer period of time.

Sulfur dioxide is another gas with a long history as an antimicrobial, as it is effective against bacteria, molds and yeasts. Applications include wine, dehydrated fruits and vegetables, fruit juices, syrups, pickles, and fresh shrimp. It is most effective at pH values below 4.0. Food manufacturers have decreased its usage in recent years due to a variety of health concerns; these include reports from asthmatic individuals of reactions to sulfur dioxide and consumers associating headaches with sulfite consumption.

Ozone, the gas that protects the earth from UV radiation, is a proven fruit and vegetable sanitizer. Ozone molecules form when ordinary oxygen molecules containing two oxygen atoms are forced to take a third. Ozone's action as a sanitizing agent comes from its unstable molecule structure - the third oxygen atom tends to break apart from the ozone molecule, releasing energy. When fruits and vegetables are exposed to ozone, surface bacteria absorb the highly unstable molecules. When that third oxygen atom breaks away, the bacteria explode. Tests have shown an ozone-enriched water wash kills almost all the bacteria on produce samples, along with some yeast and mold, increasing shelf life of fresh produce by up to two weeks. It also retards softening and browning.

Many other naturally derived ingredients prevent microbial growth in foods, and thus prolong freshness. One receiving much press these days is lactoferrin, a bioactive milk protein isolated from milk known to enhance human immune function.

The term "activated lactoferrin" describes a unique combination of natural ingredients that mimic the optimum environment necessary for lactoferrin to have maximum antimicrobial activity. This ingredient combination is patented in the United States under the brand name Activin(tm).

In January 2002, USDA approved the use of activated lactoferrin on fresh beef. In October 2003, National Beef Packing Co., LLC, Kansas City, MO, the nation's fourth-largest beef processor, commenced using Activin on its products. "We are fully committed to providing consumers with the safest, most-wholesome and most-nutritious beef possible," says John Miller, CEO. "The ability to use a natural ingredient to further-protect consumers against harmful bacteria is a significant step not only for National Beef, but for the entire industry as well."

Activated lactoferrin protects beef from pathogenic bacteria by detaching pathogens already attached to the meat, preventing other pathogens from adhering and inhibiting pathogen growth. Research shows that Activin protects beef against E. coli 0157:H7, Salmonella, Listeria and more than 30 other types of pathogenic bacteria. It does not affect the nutritional, taste, texture, color or aging qualities of beef products.

According to Miller, Activin will be included as the final step in the company's existing food-safety interventions. The system includes an electrostatic application of the activated lactoferrin, followed by a water rinse to detach any remaining pathogenic bacteria from the meat surface. However, the question remains: Under the current FDA definition, are beef products treated with lactoferrin still "fresh?"

Organic acids, such as acetic, citric, propionic and sorbic acids, and their soluble salts (i.e., calcium, potassium or sodium) can also effectively control the growth of select microorganisms by lowering the pH of food. Foods with a pH below 4.5 are considered acidic, and many microorganisms will not proliferate in such an environment. Organic acids occur naturally in some foods and may also be added as an ingredient or accumulate as a result of bacterial fermentation.

When attempting to keep food fresh, the first line of defense is to destroy bacteria, mold and yeast, as microbial growth is typically the first sign of food-product breakdown or decay. However, manufacturers can also add ingredients for the sole purpose of keeping finished products fresh. They must label some of these as preservatives, while others can simply be listed on the ingredient statement.

For example, fat-containing foods always run the risk of lipid oxidation, which can be detrimental to a food's sensory attributes. Lipid oxidation occurs when atmospheric oxygen combines with unsaturated fatty acids (containing one or more double bonds), producing compounds that can negatively affect a food's appearance, odor and taste, which is described as "rancid" or "stale" - all the opposite of fresh.

Antioxidants can slow oxidation by blocking free-radical formation by donating electrons or hydrogen ions to halt the oxidative process. This extends the shelf life of fat-containing foods. In general, the more double bonds in the fatty acid, or the higher the degree of unsaturation, the greater the probability that it will oxidize if left unprotected. Keep in mind that antioxidants protect fats or oils from oxidation but do not rejuvenate already oxidized fats or oils.

The most commonly used man-made antioxidants are butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate and tertiary-butylhydroquinone (TBHQ). These ingredients are FDA-approved for specific applications, with many having maximum usage levels.

If fresh and natural are the goal, an alternative to synthetic antioxidants is the tocopherols (vitamin E), which are found in vegetable oils, as well as grains, seeds and nuts. They protect fats and oils from oxidation, keeping them fresh. Tocopherols work best is in food products that are naturally deficient in antioxidants, such as prepared foods containing a mixture of fats. They exist in four forms - d-alpha, d-beta, d-gamma and d-delta - with the gamma and delta forms the most active for stabilizing fats. Ingredients that contain all four forms are referred to collectively as "mixed tocopherols." Manufacturers typically add mixed tocopherols to foods for their antioxidant activity. These ingredients do not impart flavor, color or odor to final food applications and are effective at very low concentrations.

FDA allows the use of tocopherols in most food applications. Typical usage levels are 0.01% to 0.02% of a food's total fat content. Food products formulated with tocopherols typically state their inclusion in the ingredient statement as "Natural vitamin E added to preserve freshness," or "Natural vitamin E added to protect flavor."

Another way to slow oxidation is to identify the presence of factors that catalyze oxidation, such as heat, light and the presence of trace metals and various pigments, and control them. For example, a way of controlling trace metals is to add sequestering/chelating agents such as citric acid, ethylenediaminetetraacetic acid (EDTA) - which occurs as calcium disodium EDTA and disodium dihydrogen EDTA - and phosphates. These ingredients inhibit metals from initiating undesirable lipid oxidative reactions by forming strong complexes with the metal ions.

EDTA blocks copper and iron from catalyzing oxidative chain reactions. It is FDA-approved for use in various vegetable oil-based products. USDA also allows manufacturers to add citric acid to meat products with a high iron content. And phosphates such as sodium tripolyphosphate and tetrasodium pyrophosphate also sequester metal ions; however, they are primarily added to meat products to improve moisture retention, which, of course, contributes to perceived freshness.

Moisture retention in certain foods, such as bakery products, is key to maintaining perceived freshness, as it prevents staling. "Manufacturers of bakery products continue to look for ways to extend the shelf life and enhance the textural properties of cakes, cookies and other sweet goods," says Dan Putnam, technical manager, Grain Processing Corp., Muscatine, IA. Starch can aid this endeavor. "Our new Inscosity(r) B656 food starch-modified improves moisture retention, softness and eating quality of bakery products," he says. "In extended frozen storage, the starch helps prevent shrinkage and moisture loss. Furthermore, a frozen cake that includes this ingredient tastes fresh after being thawed and stays moist for several days in the bakery or grocery store."

This starch also instantly hydrates, which controls batter viscosity. Use levels range from about 0.5% by weight in a cookie formulation to 0.8% in muffin or cake batter. Of course, FDA's "fresh" definition excludes all bakery products, regardless of the ingredients used in their manufacture, as the baking process itself eliminates the use of the term.

In summary, the descriptor "fresh," as it relates to foods, is very limited by FDA. Though many in the food industry support changing the definition in order to accommodate new technologies - process-, package- and ingredient-related - if manufacturers employ any of these technologies today, they likely cannot call the food "fresh." However, they can call themselves proactive and progressive, and customers will see the improvement.

Donna Berry, president of Chicago-based Dairy & Food Communications, Inc., a network of professionals in business-to-business technical and trade communications, has been writing about product development and marketing for 9 years. Prior to that, she worked for Kraft Foods in the natural-cheese division. She has a B.S. in food science from the University of Illinois in Urbana-Champaign. She can be reached at [email protected].

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