March 3, 2022 at 11:43 am | Updated May 2, 2022 at 6:50 am | 6 min read
The way food is purchased and consumed has undergone enormous changes in the last few decades. Consumers demand food that is minimally processed and nutritious with no chemical additives. At both the national and international levels, stringent controls on food are in place to protect consumers’ health. Also, changing retail and distribution methods are making older packaging systems inadequate. Newer technologies better suited for the current, rigorous market needs are developing, and active packaging is one of them.
What is Active Packaging?
Modified atmosphere packaging (MAP) alters the gas mixture in a package to protect and preserve food. These packages contain manipulated compositions of carbon dioxide (CO2), oxygen (O2), and nitrogen (N2) to preserve appearance, texture, taste, freshness, and hygiene while extending shelf life and quality.
The modified atmosphere has higher levels of CO2 and lower O2 than outside air to reduce respiration and biomass loss, control microbial spoilage, and preserve food quality.
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Sulfur dioxide (SO2), carbon monoxide (CO), argon (Ar), and ethanol (CH3-CH2OH) are also used to a limited extent in MAP.
The targeted gas composition can be monitored with small portable devices, such as the F-920 Check It! Gas Analyzer, manufactured by Felix Instruments – Applied Food Science. The F-920 is a headspace gas analyzer that takes rapid CO2 and O2 measurements.
Broadly, the maintenance of modified atmosphere inside the package occurs in two ways: active and passive.
- Passive MAP, which uses the properties of the food product and the permeability of the packaging material to achieve and maintain the desired atmosphere, is suitable mainly for respiring food, such as fresh produce. The respiration produces CO2 and maintains a high level of this gas, which is the aim of MAP. Though cost-effective, passive methods require time to realize the optimal atmosphere and are unsuitable for short-term packaging.
- Active MAP is a relatively recent innovation. A vacuum is created to remove air, and then the targeted atmosphere is added. Along with additives and suitable packing materials, this maintains the new modified atmosphere in the package. Stakeholders can use this kind of packaging for all kinds of food products: respiring fresh produce and non-respiring animal products, processed food, and pharmaceuticals. Active technologies are more expensive than passive methods.
Functions of Active Packaging
Active packaging is engineered to respond to changes in the atmosphere inside and outside the package. The aim of active packaging can differ depending on the food product; therefore, there are a wide range of technologies used in active packaging.
Active packaging can extend shelf life and improve food quality by influencing the following processes:
- Physiology; e.g., respiration, ripening, and transpiration in fresh produce
- Chemistry; e.g., oxidation of oils and fats
- Physical processes; e.g., powders caking and bread staling
- Microbiological spoilage due to bacteria, fungi, and yeast
Active packaging can be used for various food groups and by targeting different processes, as shown in Figure 1.
As shown in Table 1, there are two types of technologies used:
- Absorbers or scavengers to remove undesired components like O2, CO2, ethylene, odor, microbes, and moisture.
- Emitters that add desired elements to the MAP like CO2, scents, antioxidants, and antimicrobial substances.
Removing excess moisture within packages by including desiccants in dry products was one of the first use of active packaging. Desiccants can be in the form of tablets, sachets, pouches, patches, or coupons. The first use of desiccants was not for food but metals and hardware.
The desiccants remove excess water vapor, impacting the quality and texture of moisture-sensitive food. The excess moisture causes caking in powders or softening in crisp snacks like chips, sweets, and candy.
There are two types of moisture absorbers:
- Liquid absorbers are hygroscopic pads or sheets that absorb moisture present as a liquid in fresh produce, meat, fish, and poultry to prevent microbial infection and degradation of sensory attributes.
- Relative humidity regulators or desiccants absorb water vapor to regulate relative humidity. These could be deliquescent salts, such as calcium chloride and magnesium chloride. They are added as sachets and labels in dry foods that produce low amounts of moisture like snacks, powders, cereals, nuts, spices, etc.
Depending on the material used, moisture absorbers could be:
- Chemicals such as silica gel, modified starch, natural clay, calcium oxide, and calcium chloride.
- Molecular sieves that absorb extra moisture even in high temperatures.
Technologies to remove oxygen are the most widely used active MAP. In some cases, packaging aims to reduce oxygen levels to 1 or even 0.01%.
The oxygen scavengers prevent the adverse effect that O2 causes through several reactions that affect food like oxidation and rancidity of fats and oils, ripening and senescence of fresh produce, staling of bakery products, and encouraging aerobic bacteria that can spoil food.
Ordinarily, MAP aims to remove O2 from packages, but in some cases, such as retaining the fresh red color of meat or for surface ripening through the mold of cheese, a small quantity of O2 is needed to get the necessary biochemical reactions or encourage certain microbes.
O2 scavengers are made of iron and ferrous salts that chemically combine with O2 to remove them from the headspace of a package. One gram of iron reacts and removes 300 ccs of O2. Other materials used as O2 scavengers are sulfites, enzymes, boron, photosynthetic dyes, etc.
O2 scavengers are classified based on the following:
- Activation mechanism, which can be water, UV rays, or auto-activation
- Form, which can be flexible gas permeable sachets, extrudable parts embedded in the plastic polymer, and label
- Reaction speed, where the effect is fast, medium, or slow
- Mode of action, where scavengers remove O2 chemically or physically
These techniques are combined with removing all oxygen in the packages first and using packaging materials that are effective barriers to O2 in the outside atmosphere.
O2 scavenging compounds are applied to:
- beer bottles, meat products, baked goods, pasta, pizza, coffee, dried foods, oils, fats, snack foods, processed meat, etc.
- dairy products, like probiotic yogurt, milk, etc., O2 to maintain the viability of Lactobacillus acidophilus and prevent stale odor development by reducing O2 by 23-28%.
Carbon Dioxide Management
CO2 management could include removing or adding the gas with the help of scavengers and emitters, respectively.
In fresh meat, fish, fresh produce, dried fruits, nuts, snacks, and baked goods, CO2 levels are kept high. Often concentrations of up to 99% of the headspace are used, as the gas has antimicrobial effects.
When the package contains non-respiring food, active CO2 emitters produce and release the gas. This helps to control microbes, which cause spoilage and extend shelf life. In fish and shellfish, the CO2 levels can be between 10-80%. Often CO2 emitters are used in combination with O2 scavengers to control aerobic microorganisms and maintain the targeted MAP, especially for fresh meat products.
High CO2 levels also decrease fruit softening rates and pigment retention.
CO2 emitters are usually chemicals, such as ferrous carbonate or a mixture of ascorbic acid and sodium bicarbonate. They are present as pads and box systems.
CO2 removal is necessary in some cases when the products are CO2-sensitive, such as mushrooms. It is also necessary to remove the CO2 produced so that the package does not burst. CO2 scavengers are used for coffee, cheese, and fresh produce.
CO2 scavengers include:
- Chemicals like calcium hydroxide, sodium hydroxide, silica gel, potassium hydroxide, and calcium oxide.
- Biofilms that can absorb the gas. These are sometimes used as labels for fresh produce and mushrooms.
Table 1: “Current and Potential Future Applications of Active Packaging Technologies,” Muredzi 2013. (Credits: https://www.researchgate.net/publication/264787890_Active_Intelligent_and_Modified_Atmosphere_Packaging_A_Model_Technology_for_the_Food_Industry)
In long-term cold storage, ethylene scavengers are used to remove the phytohormone, as it can speed up the ripening and decay of climacteric fruits like bananas, tomatoes, and mangoes, as well as ethylene sensitive, non-climacteric products like carrots and onions.
Ethylene scavenging can also absorb ethylene produced by the natural ripening process, causing damage to fresh produce.
The following materials are used as ethylene scavengers in the form of film and sachets:
- Potassium permanganate, which reacts chemically with ethylene.
- Activated carbon and finely dispersed zeolite’s fine pores, which absorb ethylene.
Using ethylene scavenging improves fresh produce and horticultural products’ firmness, color, texture, taste, and longevity.
Substances are added to the packaging material to absorb off-flavors and odors produced during the breakdown of food, such as fish, dairy products, fruit, and poultry.
- Common odor absorbers are activated carbon, citric acid, cellulose triacetate, acetylated paper, ferrous salts, clays, and sodium bicarbonate.
Substances are also added to improve the flavor or scent of a product to make it more attractive for consumers. These are added to fruits, fruit juices, and snacks. The following materials are used to improve the organoleptic quality of food products:
- Activated carbon or additives to plastics, such as polyester, polyethylene and polypropylene polyamide, and polyvinyl chloride.
Antimicrobial substances are the largest group of emitters used in active packaging to control microbial spoilage in fresh produce, meat products, bakery items, and cheese.
The most commonly used substances, besides carbon dioxide, are ethanol and sulfur dioxide. Other additives are sorbates, benzoates, propionates, silver salts, sulfur and mercury compounds, zeolites, bacteriocins, and sub-micrometer wall penetrants.
These can be in the form of coatings, sheets, labels, films, interleavers, and silver-based masterbatch, trays, and films. Sachets and insertions in the headspace are also used.
A wide variety of antimicrobial packaging exists, but most antimicrobial substances are not used due to legislation, sanitary considerations, consumer resistance, and high costs.
Optimizing Active Packaging
Some other technologies used in active packaging are chemical stabilizers, enzyme inhibitors, and antioxidants.
Active packaging is promising and has several advantages over traditional packaging. It also has the potential to reduce food loss and waste and make agriculture more sustainable. However, continued research is required on the materials and mechanisms involved to ensure that they do not negatively impact food quality and safety and do not pose any health risks for consumers.
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