Food Engineering

ESL for Refrigerated Foods Maintaining the Chain

April 10, 2003
Extended Shelf Life for Refrigerated Foods A number of technologies can deliver longer shelf life.

US food industry consolidation is resulting in fewer, larger plants, expanded distribution areas and increased demand from retailers for quality products. Meanwhile, consumers are also presenting a long list of demands to food processors, requesting foods that are convenient, flavorful, healthy, fresh, already prepared or easily prepared, and portable.

All of these factors are leading producers of refrigerated foods to consider extended shelf life (ESL) technologies in order to provide fresh, healthy products and to allow them to ship products farther and significantly widen their markets.

There are a number of food processing and packaging technologies to help safely achieve a longer shelf life. But before employing any of these technologies, food and beverage manufacturers must consider one thing first and foremost - hygiene – says Dr. Gail Barnes, marketing manager, Global ESL Category, Tetra Pak ESL Application Center, located in Buffalo Grove, IL. “One can’t stress enough how important the hygiene focus is [when employing ESL technologies]. From the corner office to the factory floor, it’s the foundation on which ESL technology exists.”

Barnes notes that in addition to the hygiene foundation, processors need to take a systems approach to achieving an integrated ESL system, utilizing reliable processing and packaging equipment each step of the way. “Just like links in a chain, each [system] needs to be the same strength; there can be no weak link because ESL technology is only as strong as the weakest link in the chain,” adds Barnes.

Generally, there are three different methods, or “hurdle technologies” that can be used to provide safe ESL refrigerated foods. These include thermal processing, which includes hot fill, quick chill technologies, and pasteurization methods; non-thermal technologies including high pressure processing, irradiation, and use of ultraviolet light treatment; and finally packaging hurdle technologies including modified/controlled atmosphere packaging, clean room utilization, and active and “intelligent” packaging systems.

Land ‘O Lakes’ new Grip‘n Go line of regular and flavored milks in 12 oz. HDPE bottles are packaged using ESL filling which provides a 50-70 day shelf life.

Adding value to liquid dairy

Existing ESL technologies such as high temperature processing or “ultra pasteurization” are helping the dairy segment move into higher-margin, value-added products including flavored milks, soy and hybrid soy/dairy products, and functional dairy products, by offering shelf lives of 60-90 days. Processing temperatures range from 240?F up to ultra heat treatment (UHT) of approximately 284?F.

Dr. Barnes, presenting research results on ESL technology for chilled products at the International Dairy Federation’s World Dairy Summit, predicts growth in total ESL liquid dairy products from 1.1 billion liters (3.1 percent of the total chilled dairy market) in 1998 to 8.1 billion liters (22.3 percent of the total chilled dairy market) by the end of 2003. Most of this growth will come from the U.S., the U.K. and Japan, says Barnes.

Just one look at the refrigerated dairy case in any U.S. supermarket backs up these numbers. By employing ESL technologies, single-serve dairy-based beverages can now compete with carbonated soft drinks and juice drinks for the on-the-go consumer dollar.

Joining the hugely successful Milk Chugs from Dean Foods and Nestle’s Nesquik brands is Land ‘O Lakes’ new Grip‘n Go line of regular and flavored milks in 12 oz. high-density polyethylene bottles packaged using ESL filling that provides a 50-70 day shelf life. Another offering in this expanding category is Smith Dairy Products’ Moovers brand flavored milk in PET bottles, which boasts a 60-day refrigerated shelf life. The bottles feature an amber tint to keep out milk-degrading ultraviolet light and are filled on a sterile ESL filler from Serac Inc. (Carol Stream, IL).

Land ‘O Lakes’ new Grip‘n Go line of regular and flavored milks in 12 oz. HDPE bottles are packaged using ESL filling which provides a 50-70 day shelf life.

HPP hits new product segments

As an alternative to thermal processing technologies such as ultra pasteurization for dairy products, non-thermal processing techniques including high pressure processing (HPP) is garnering more attention as a way to extend shelf life of foods while maintaining a better retention of the food’s flavor, texture, color and nutrients. HPP employs ultra-high pressures of 30,000-130,000 pounds per square inch (psi) for a specified temperature and time, which inactivates most pathogenic microorganisms commonly found in the foods.

While high pressure processing has been used commercially in Japan for the past 10 years, it is now making inroads in North American and European markets. HPP is said to be gaining popularity with food processors as an alternative to thermal processing not only because of its ability to achieve longer shelf life and retain the food’s freshness, flavor and color, but also its reduced processing time and energy requirements and its minimal heat penetration.

“Studies on orange juice [using HPP] have shown an acceptable shelf life after 21 weeks. Typically, though, food processors can at least double the shelf life of most products with high pressure processing,” according to Retail Prepared Refrigerated Foods: The Markets and Technologies, a recent study from Food Spectrum, LLC, published in conjunction with the Food Policy Institute at Rutgers University.

Another advantage of HPP is that you can process the food directly in the packaging, notes National Center for Food Safety and Technology (NCFST) Director Charles Sizer. “If you use conventional thermal processing for something like luncheon meat, you melt the fat and then the packaging material gets covered in fat,” says Sizer. “Using high pressure, you can put it in cold, and the melting point is higher.” Sizer claims that 60-70 percent of foods in the frozen food aisle are candidates for high pressure processing.

While the cost of high pressure processing is slightly higher (two to three cents per pound) than conventional methods, Sizer says as the volume of HPP applications increases, the cost will become more reasonable.

Today, worldwide commercial products that currently use high pressure processing include orange juice, guacamole and salsa, sliced ham, oysters, clams, mussels, scallops, shrimp and crab meat, and jams, jellies, and fruit desserts. One particular success story for HPP involves Avomex (Keller, TX), which launched the first commercially available product in the U.S. processed with HPP equipment for its guacamole, which has been selling in supermarkets in the southern U.S. for nearly two years. The company wanted to extend the shelf life of its fresh, chilled guacamole from a few days to five weeks or more to increase its distribution area. After trying heat treatment, flash freezing and modified atmosphere packaging, high pressure processing was found to be the best alternative.

The company, which uses HPP units from Flow International of Kent, WA, is also considering using high pressure for processing its carrot and apple juice, garlic puree, mango, guava and other sub-tropical fruit and vegetables.

In the world’s largest milk markets, ESL liquid dairy products are forecast to increase from 1.1 billion liters in 1998 to 8.1 billion liters in 2003.
While earlier refrigerated products treated with HPP included juices, guacamole and salsa, more recent activities have centered on refrigerated prepared foods and value-added meat products, according to the Food Spectrum study. HPP technology is forecast to find broad application in this growing segment of the food industry.

The study cites the fact that in January 2001, Hormel Foods announced it would use Flow International’s HPP units in its Austin, MN, plant to produce a variety of prepared ham products. In February 2001, Perdue also saidit would use high pressure to process a variety of prepared poultry products.

The future of high pressure processing may involve preservation of low-acid, shelf-stable foods. It may be possible to use HPP successfully by combining moderate heat of 176-230?F with very high pressures up to 130,000 psi. A new research project at the NCFST, in partnership with Flow International, U.S. Army Soldier System Command, Kraft Foods, Procter & Gamble, and ConAgra, is currently assessing the potential of HPP for producing high-quality, shelf-stable foods.

Packaging’s role in ESL

A variety of packaging methods can offer just as many ways to extend shelf life of refrigerated foods as different processing methods. Modified atmosphere packaging, which employs natural gases such as carbon dioxide combined with high-barrier packaging films, has proven to be very successful at extending shelf life of various refrigerated foods. Now, “active” and “intelligent” packaging methods are being developed that can be specifically tailored to the refrigerated food or beverage product to help lengthen shelf life and slow microbial growth.

Active packaging technologies are broadly defined as technologies that interact with food and beverage products and sense environmental changes and respond proactively by changing their properties to maintain, adjust, or improve a specific atmosphere to improve product quality, safety and shelf life. Oxygen scavengers, a form of active packaging that has been used for a number of years, have been incorporated into food packaging at a rate 15 times greater than in 1990 and their use is projected to grow by 15 percent or more annually, according to Dr. Aaron Brody, president of Packaging/Brody, Inc., speaking at Packaging Strategies’ ActivePack 2002 conference earlier this year.

Among the newer active packaging technologies, Boston, MA-based antimicrobial company AgION Technologies, L.L.C. recently launched its silver-based natural inorganic antimicrobial AgION. Moisture in the air causes a controlled release of the silver ions at a slow and measured rate that is said to effectively maintain an antimicrobial surface of a variety of packaging films, thereby increasing shelf life.

Another “active” technology used to help extend shelf life is BP’s Amosorb active barrier made from polyester which reacts with oxygen to provide enhanced barrier for oxygen-sensitive products. BP recently introduced Amosorb DFC (direct food contact) to be used in direct contact with foods and beverages in either monolayer or multilayer bottles.

Microsphere technology, currently being developed by Bernard Technologies, Inc. (Chicago, IL), is a system developed to reduce microbial food contamination. Where many active packaging technologies work to take something out of the package environment, the Microsphere system generates, on demand, controlled amounts of chlorine dioxide gas, an extremely potent biocide, in the package environment. Possible applications of the Microsphere technology include antimicrobial plastic film, sachets, rigid containers and paperboard coating.

Maintaining the cold chain

While processing and packaging technologies are becoming ever more sophisticated in reducing spoilage organisms and extending shelf life, maintaining the cold chain is a crucial part of successful ESL technologies. “Temperature is the most important and most obvious criteria for maximizing the shelf life of refrigerated foods, yet it is frequently misunderstood and overlooked,” notes Food Spectrum’s study.

Despite the fact that the current industry standard for refrigerated holding conditions is 40?F, “various surveys have shown that the temperature of foods in U.S. chilled food distribution channels are frequently in the range of 45?F-55?F,” notes the report.

The Retail Prepared Refrigerated Foods study recommends “superchilling,” also called “sub-zero degree chill” solutions to help inhibit growth of a majority of pathogenic and food spoilage microorganisms. Superchilling is generally agreed to be the temperature from 28.4?F-35.6?F (just above the freezing point of the product). According to the report, at these deep chill temperatures, most microbiological activities are kept at a minimum and when these temperatures are continuously maintained, it has been determined that the shelf life is 1.5 to four times greater than conventional refrigeration temperatures of 39-46?F.

Should we limit shelf life?

Do all of these efforts to extend shelf life come at the expense of food quality, questions Lou Cooperhouse, president and ceo of Food Spectrum. Cooperhouse proposes limiting shelf life in order to maximize the culinary characteristics of products, minimizing the opportunity for foodborne disease, providing realistic product shelf life dating, and assuring a truly fresh product.

Cooperhouse claims that many in the food industry believe that local or regionalized manufacturing and distribution centers that can tailor products to localized tastes will ultimately be successful.