Smart Packaging for Shelf Life and Safety

Active packaging extends food shelf life using technology beyond traditional packaging barrier technology. Intelligent packaging communicates by acquiring, storing, processing, and sharing information across the entire value chain. Both have been commercially successful, and innovations continue.

Getting Active

Active packaging employs features to extend the shelf life of food without relying solely on package barrier properties. Modified atmosphere packaging (MAP) and antimicrobial packaging are two core areas of active packaging.

MAP technology extends food shelf life by modifying the gas composition within the package, primarily by reducing oxygen levels and replacing it with gases like nitrogen or carbon dioxide, thereby inhibiting lipid oxidation and microbial growth. MAP is used for foods with high unsaturated fat such as snack foods and some cereals, produce, bakery, meat, and cheese, since altering the oxygen level can stall microbial growth as well as oxidation and other deteriorative reactions in these foods.

Vacuum packaging is a form of MAP that involves removing all headspace and oxygen from the package. It is crucial to maintain refrigeration for products with a water activity above 0.85 or 0.92, depending on the pH, as the absence of oxygen can pose a risk for unprocessed foods. The pathogen Clostridium botulinum thrives in environments with 0% oxygen when not refrigerated. Therefore, foods susceptible to this risk must follow a strict cold chain, verified through intelligent packaging or shipping temperature records. In other scenarios, oxygen levels are maintained above 0%.

For foods with high water activity and unsaturated fats, lipid oxidation can result in oxygen consumption and a subsequent reduction of package headspace oxygen. For foods that pose a risk for C. botulinum growth, the oxygen level is determined by the need to inhibit mold growth in a low-oxygen environment, the need to have a low oxygen level to stall lipid oxidation, and the need to maintain oxygen above 1%. Interestingly, the oxidation of unsaturated fats can lower oxygen levels and then inhibit mold growth if the oxygen levels stay below 3% and safely above 0%. The oxygen level is often a critical control point within the Hazard Analysis and Critical Control Point (HACCP) process for MAP. Optimal headspace gases of carbon dioxide, oxygen, and nitrogen vary within produce packaging, are a function of respiration rate, and can vary based on harvest time, cultivar, and weather during the growing season. Oxygen also is controlled using oxygen absorbers such as sachets or embedded within the package material and microperforations.

Antimicrobial active packaging is used in polymers or paperboard. For antimicrobial packaging to slow microbial growth, direct product contact is needed or the antimicrobials must be sufficiently released from the packaging into the headspace above the product. In both cases, migration from the packaging into the product or headspace is required. This migration of antimicrobials is a function of the partition coefficient, the relationship between the migrant concentration within the package material, and the amount that actually will migrate from the package material. The food itself also impacts the rate and amount of antimicrobial migration from packaging, particularly high-fat foods that can polymerize or open structures, resulting in higher levels of antimicrobial migration. Thus, concentrations of antimicrobials within packaging required for efficacy vary significantly.

Commercial antimicrobial films include metal ions and nanoparticles of silver and zinc oxide. Silver nanoparticles present an issue because when waste from food that has been exposed to packaging containing silver is used as compost, the silver enters into cropland. Packaging containing silver can also be disposed of improperly as litter and can contaminate waterways and land. By contrast, zinc oxide does not present these issues and is generally recognized as safe (GRAS), effectively inhibiting yeast, molds, Listeria monocytogenes, and Staphylococcus aureus. Zinc oxide’s low-temperature efficacy makes it promising for chilled foods, and it has been commercialized for vacuum-packaged meat.

While zinc requires direct product contact to be an effective antimicrobial, volatilized gases are effective in the package headspace. Chlorine dioxide inhibits mold, yeast, L. monocytogenes, Bacillus cereus, Escherichia coli, and S. aureus on foods within a package. Commercial applications include releasing chlorine gas through channels within polymer film and related polymer film applications. Similarly, sulfur dioxide gas extends the shelf life of berries by preventing mold growth. It is released from concentrated pads placed within individual packaging containers or within pallets shrouded to contain the sulfur dioxide gas. Ethanol is used as a processing aid and flavor carrier in the bakery industry to inhibit mold, yeast, and L. monocytogenes.

Inherently, antimicrobial films such as chitosan hold promise in mold and yeast inhibition. Bacteriocins and essential oils are antimicrobials best applied directly to food as edible antimicrobial coatings, which are then essentially food coatings or processing aids. Notably, active coatings have been developed by coordinated researchers at the Vietnam Institute of Agricultural Engineering and Post-harvest Technology (VIEP) and Vietnam Academy of Science and Technology. For example, Nguyen Manh Hieu’s VIEP research group extended the shelf life of pomelo to 45 days and prawn to 90 days using antimicrobial barrier coatings.

Other bacteriocins are also best applied directly onto foods. These include lysozyme, lactoferrin, and lactoperoxidase, which are, to varying degrees, effective against yeast and molds but not effective against L. monocytogenes and B. cereus. In contrast, the bacteriocin nisin is effective against L. monocytogenes, B. cereus, and S. aureus. Coatings using essential oils and natural extracts such as cinnamon, grapefruit seed extract, and mustard (allyl isothiocyanate) are effective against mold growth. Interestingly, oregano has shown some efficacy in combatting L. monocytogenes and B. cereus.

Intelligence Counts

By verifying the food quality and/or safety of packaged food, intelligent packaging adds value across the entire value chain. Intelligent packaging simplifies retailer stock rotation and reduces consumer-generated food waste by monitoring product freshness after opening the package. This is important in food waste prevention since much of food waste is consumer- and retailer-derived. Higher food prices, laws against food waste like those in Vermont, the 40% surge in Listeria, Salmonella, and E. coli cases in 2024, the dissolution of the National Advisory Committee on Microbiological Criteria for Foods, the National Advisory Committee on Meat and Poultry Inspection, and other governmental bodies responsible for food safety point to the need to implement intelligent packaging to communicate food safety and quality effectively.

Communicating product quality and safety via intelligent packaging has been used since at least the 1970s with the use of time-temperature indicators and integrators (TTIs). Indicators let users know if a specific temperature has been reached, whereas integrators integrate time and temperature and provide a clear yet indirect link to deteriorative reactions. Measuring time and temperature is critical because deteriorative reactions of lipid oxidation, enzymatic browning, non-enzymatic browning, and microbial growth increase are a function of temperature and time. The U.S. Food and Drug Administration specifies the use of TTIs with selected seafood, and they are used extensively by military and world food aid programs to ensure that food is safe and contains the required nutrients. TTIs are used extensively in business-to-business operations and are linked with real-time temperature and time monitoring during shipments.

Sensors that sense and communicate changes in food are directly linked to shelf life and quality. The most prevalent indicator, a pH indicator, has abundant applications since many foods exhibit pH changes as shelf life deteriorates. Other intelligent direct sensors measure specific reaction byproducts. Meat spoilage is measured by sensors that quantify total volatile basic nitrogen, cysteine loss, or hydrogen sulfide generation. Produce quality sensors measure ethylene or carbon dioxide, and sensors for fish detect volatile amine formation.

Sensors can also be integrated into the packaging structure using functional inks with conductive, chromogenic, photochromic, and thermochromic properties. These indicators are food specific. For example, carbon dioxide absorbers, calcium hydroxide, and dyes of bromocresol purple or methyl red within a polypropylene-based package monitor the degree of fermentation within kimchi. Measuring Campylobacter, Salmonella, and Shigella is accomplished with phage receptor-binding protein sensors. Other sensors convert biochemical signals to electrical responses that show remaining shelf life. Sensors play a key role in communicating food safety to consumers and retailers. The obstacles of cost and false positives, such as sensors indicating food is safe when it is not safe, are eroding as costs decline and enhanced precision has mitigated apprehensions about measurement and reading errors.

Making the Connection

Connecting intelligent and active packaging is the next critical step for packaging innovation. This integration would use intelligent packaging to detect spoilage, and then active packaging would be triggered to mitigate the spoilage. For example, if microbial growth is sensed in packaged meat, antimicrobials can be released to inhibit further growth. This would allow preservatives to be released only when needed and extend food shelf life. Regardless, current technologies in active and intelligent packaging present many solutions to both extend and sense food shelf life.ft