First of all, let’s remember the definition for Active Packaging given in the first post of the Smart Packaging series:
Active Packaging is accurately defined as “packaging in which subsidiary constituents have been deliberately included in or on either the packaging material or the package headspace to enhance the performance of the package system” (Robertson, 2006).
Active packaging is an extension of the protection function of a package. Some examples are:
– Moisture level control (e.g.by using sorbents) which will reduce the water activity and, prevent the proliferation of germs and avoid softening the texture of food.
– Oxygen level in sensitive beverages (beer, wine, juices) to increase their shelf-life
– Control substances that may alter the product appearance (e.g. table salt inhibits the formation of condensation and prevent discoloration in mushrooms).
Broadly speaking most of active packaging is usually destined to extend the product shelf life by absorbing/removing chemicals, increasing barrier properties (mainly from oxygen and moisture.) or by using as bacteriocidal or bacteriostatic agents.
As mentioned on the first post of this blog Active Pakaging can play a crucial role in decreasing the huge amounts of food waste in both Industrialized and developing countries (respectively 670 and 630 million tonnes).
It can also be used to release substances form the container to the content (a kind of desired migration).
Another way to avoid unwanted substances in the product and to guarantee its desired attributes is to increase the barrier properties of the container (usually avoid moisture and oxygen form entering and CO2 or aromas to pass through the container).
So, I’m going to focus on Active Packaging that contributes top increasing shelf-life.
Source: Active Packaging Slideshare by Nandhu Lal
Modified Atmosphere Packaging (MAP) is not going to be durectly addressed in this post, but will probably be addressed in future posts. Meanwhile here’s an interesting article about the subject.
Absorbers / Scavengers
Water activity favors bacterial growth and mositure softens many food products, so it is no wonder that one of the oldest examples of Active Packaging is the use of silica gel sachets. Other materials used are calcium oxide and activated clays and minerals.
Molecular sieves are composed of sodium, potassium or calcium silicates and are excellent absorbers with a greater capacity compared to silica gel and clay.
There have been some developments with moisture absorbers such as Dri Fresh® Resolve®, which allows oxygen to circulate (preventing the undesired brownish color shown by meat in contact with the container).
It is composed of corn starch and a cellulosic absorber (compostable materials), and produced without using any adhesives or bonding materials.
Oxygen absorbents /scavengers (sometimes used in combination with MAP) create a low oxygen environment to avoid several oxidation reactions.
Ferrous oxide is one of the most common. Non-metallic scavengers include organic reducing agents such as ascorbic acid, ascorbate salts or catechol. There are also enzymic scavengers systems using either glucose oxidase or ethanol oxidase.
VOC (Volatile and Odor Control)
It is also interesting to absorb substances that will affect the organoleptic properties of the content (VOC Volatile and Odor Control).
Some examples could be limonin (which causes bitter in citrus juices could be removed by acetylated paper, or cellulose acetate gel beads. The unpleasant smelling volatile amines, such as trimethylamine in fish can be neutralized by various acidic compounds (like in this patent).
Ethylene (CH2=CH2) can ripen or mature perishable products (such as fruits, vegetables and flowers).
Most fruits and vegetables release ethylene after they are harvested. Ethylene is a phytohormone that initiates and accelerates ripening, produces softening and degradation of chlorophylls, and inevitably leads to deterioration of fresh or minimally processed fruits and vegetables.
The control of ethylene in stored conditions plays a key role in prolonging the postharvest life of many types of fresh produce.
RELEASERS / EMITTERS
Carbon dioxide is used to suppresses microbial activity and therefore prolong the shelf life of packed food. However, CO2 permeability is much higher than that of O2 in most plastic films, so it must be continuously produced to maintain the right concentration. Due to the changes in taste high CO2 levels can cause, CO2 generators are only useful in certain products such as fresh meat, poultry, fish and cheese packaging.
Interesting solutions include a carbon dioxide scavengers, or a or a dual-action oxygen scavenger and a carbon dioxide scavenger system (e.g. pouches with a mixture of calcium oxide and activated charcoal for coffee).
Here’s an example of a pad extend the shelf life of a package of fresh cod by four extra days.
And here’s another one:
Ethanol is used mainly as an antimicrobial agent.
Ethanol can be sprayed directly onto food products just prior to packaging.
We have seen the antibacterial properties of CO2 and ethanol emitters, but several more examples of antibaterial packaging will be shown on the next post.
By using packaging materials with different permabilities packaging can significantly reduce adsorption, desorption, and diffusion of substances that affect the shel-life of food products.
Usually a low permability to oxigen and moisture is useful to maintain the quality of food.
This is quite an extensive subject, so I’m just going to comment on the latest developments regarding microlayers.
Microlayer films are cast coextrusions up to 1000 layers, each layer from 0.02 to 5 microns thick. One of the most promising applications involves selective multiplication of the layer produced from a barrier resin such as ethylene vinyl alcohol (EVOH).
On the next post we will see some example of iincrease barrier thanks to the use of nanomaterials.
In Part 2: Antibacterial Packaging, Nanoparticles, and Controlled Release Packaging.
To be continued