Methods of Active Packaging

How we buy and consume food has undergone enormous changes in the last decades. Consumers demand food that is minimally processed, has no chemical additives, and are nutritious and of high quality. In addition, there are stringent national and international controls on food to protect consumers’ health. Also, retailing and distribution have changed, making older packaging systems inadequate. As a result, newer technologies better suited for the current rigorous needs are developing, and active packaging is one of them. 

Active Packaging

Modified atmosphere packaging (MAP) alters the gas mixture in a package to protect and preserve food. Carbon dioxide (CO2), oxygen (O2), and nitrogen (N2) are gases whose composition is manipulated to preserve appearance, texture, taste, freshness, hygiene, and extend shelf-life and quality. 

The modified atmosphere has higher levels of CO2 and lower O2 than the air to reduce respiration and biomass loss, control microbial spoilage, and preserve food quality.  

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. It is a headspace gas analyzer that measures CO2 and O2 levels rapidly. 

The altered gas atmosphere is maintained inside the package in two broad ways-active and passive.

• Passive MAP, which uses the food product’s properties and the packaging material’s permeability 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 recent innovation, where initially, a vacuum is created to remove air, and then the targeted atmosphere is added along with additives and suitable packaging materials to maintain the new MAP. This kind of packaging can be used 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, so we have 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 groups of food and by targeting different processes, as shown in Figure 1.

Figure 1: Application of active packaging, Muredzi 2013. (Credits: https://www.researchgate.net/publication/264787890_Active_Intelligent_and_Modified_Atmosphere_Packaging_A_Model_Technology_for_the_Food_Industry)

There are two types of technologies used, as shown in Table 1 are:

• Absorbers or scavengers that 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. 

Moisture Absorbers

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, which can impact the quality and texture of moisture-sensitive food. The excess moisture causes caking in powders or softening of crisp snacks like chips, sweets, and candy. 

There are two types of moisture absorbers:

●     Liquid absorbers, 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

Oxygen Scavengers

Technologies to remove oxygen are the most widely used active MAP, as in some cases, levels are reduced to 1 or 0.01%. 

The 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.

MAP aims to remove O2 from packages, except in some cases. For example, to retain the fresh red color of meat or 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, which 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 that are used as O2 scavengers are – sulfites, enzymes, boron, photosynthetic dyes, etc.

O2 scavengers are classified based on:

●     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 by removing all oxygen in the packages and using packaging materials that are effective barriers to O2 in the outside atmosphere. 

Applications:

● O2 scavenging compounds are applied to beer bottles, meat products, baked goods, pasta, pizza, coffee, dried foods, oils, fats, snack foods, processed meat, etc.

● In dairy products, like probiotic yogurt, milk, etc., to maintain the viability of Lactobacillus acidophilus to 21 days 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.

CO2 Emitters

CO2 levels are kept up to 99% of the headspace as the gas has antimicrobial effects. CO2 emitters are used for fresh meat, fish, fresh produce, dried fruits, nuts, snacks, bakery goods, etc.

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 micro-organisms and maintain the targetted 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 Scavengers

CO2 removal is necessary when the products are CO2-sensitive, like mushrooms. Or to remove CO2 produced so that the package doesn’t burst. It is used for coffee, cheese, and fresh produce.

● Chemicals like calcium hydroxide, sodium hydroxide, silica gel, potassium hydroxide, and calcium oxide. 

● Biofilms that can absorb the gas, 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)

Ethylene Absorbers

In long-term cold storage, ethylene scavengers are used to remove the phytohormone as in excess quantities, it can speed up the ripening and decay of climacteric fruits like bananas, tomatoes, mangoes, etc., and ethylene-sensitive non-climacteric products like carrots and onions. 

Ethylene scavenging can also absorb ethylene produced by the natural ripening process and damage fresh produce.

Materials used as ethylene scavengers in the form of film and sachets are:

● Potassium permanganate, which reacts chemically with ethylene

● Activated carbon and finely dispersed zeolite’s fine pores, which absorb ethylene

Using ethylene scavenging improves the firmness, color, texture, taste, and quality of fresh produce and horticultural products.

Odor management

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, poultry, etc. 

• Odor absorbers are activated carbon, citric acid, cellulose triacetate, acetylated paper, ferrous salts, clays, and sodium bicarbonate.

Substances are also added to improve a product’s flavor or scent to make it more attractive to consumers. These are added to fruits, fruit juices, and snacks. Materials improving the organoleptic quality of food products are:

• Activated carbon or additives to plastics such as polyester, polyethylene, polypropylene polyamide, and polyvinyl chloride.

Antimicrobial 

Antimicrobial substances are the largest emitters used in active packaging to control microbial spoilage in fresh produce, meat products, bakery items, and cheese.

The most commonly used substances are ethanol and sulfur dioxide, besides carbon 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 masterbatches, trays, and films. Sachets and insertions in the headspace are also used.

There is a wide choice of antimicrobial packaging, but due to legislation, sanitary considerations, consumer resistance, and high costs, most the antimicrobial substances are not used.

Optimizing Active Packaging

Other active packaging technologies 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, the materials and mechanisms involved have to be better understood to ensure that they do not negatively impact food quality and safety, and pose any health risks for consumers, as several chemicals are used. Moreover, widely used plastic is also losing consumers’ favor, so further research in active packaging technologies is needed.

Sources

Muredzi, P. (2013). Active, Intelligent and Modified Atmosphere Packaging: A Model Technology for the Food Industry. Retrieved from https://www.researchgate.net/publication/264787890_Active_Intelligent_and_Modified_Atmosphere_Packaging_A_Model_Technology_for_the_Food_Industry

Patel, R.R., Prajapati, J.P., & Balakrishnan, S. (2015). Recent Trends in Packaging of Dairy and Food Products. Retrieved from https://www.semanticscholar.org/paper/Recent-Trends-in-Packaging-of-Dairy-and-Food-Patel-Prajapati/607bcc04fc4ae049c890952f48a0565a94bacbe4

Rodriguez-Aguilera, R., & Oliveira, J. (2009). Review of Design Engineering Methods and Applications of Active and Modified Atmosphere Packaging Systems. Food Engineering Reviews, 1(1), 66-83.

Wang, H., An, D., Rhim, J., & Lee, D. (2015). A Multi‐functional Biofilm Used as an Active Insert in Modified Atmosphere Packaging for Fresh Produce. Packaging Technology and Science, 28(12), 999-1010.

Wyrwa, J., & Barska, A. (2017). Innovations in the food packaging market: active packaging. Eur Food Res Technol 243, 1681–1692. https://doi.org/10.1007/s00217-017-2878-2