- Absorbers / Scavengers
- Releasers / Emmiters
- Barrier (increasing effects)
This post is going to be focused mainly on Active Packaging that a has some kind of antibacterial (or bacteriostatic effect).I’ll pause briefly to talk about the use in Nanotechnology and also on chitosan
And finally, I’ll summarize more modern uses of Active Packaging mainly for positive migration, specially Controlled Release Packaging.
Active antimicrobial packaging (bacteria is just one of the six types of microbes: bacteria, archaea, fungi, protozoa, algae, and viruses) can be defined as a packaging system (the headspace and the packaging materials) that interacts with the food product (usually fresh or minimally processed) or the surrounding headspace, either to kill the microorganisms that might be present in the food product or food package, or to reduce, inhibit, or retard their growth and/or contaminations during postharvest transportation, storage, and retail display of the produce.
Vacuum, nitrogen-flushing, and oxygen-scavenging packaging (also commented in part one) are also used. However, technologies, which control the low oxygen concentration to inhibit the growth of aerobic microorganisms, could cause anaerobic microbial growth.
When the substances are incorporated in the packaging materials, the agents should be incorporated into/coated on the packaging layer, remain stable for a required time, and finally be released from the packaging surface in a controlled manner. Most active compounds from biological origins cannot withstand polymer processing temperatures.
The main types of antimicrobial substances used are:
- Organic acids (sorbic acid mainly, but also lactic, tartaric, malic, and acetic acids).
- Natural Microbial Metabolic Compounds (nisin from bacteria. also natamycin).
- Volatile Substances and Essential Oils (such as: rosemary, lemongrass, ginger and curcumin extracts)
- Metals (silver, titanium oxide).
Below, you can see a example of antimicrobial packaging systems studies using essential oils (you can check the complete table which includes other substances like metals and acids).
You can check this paper with examples of antimicrobial EVOH copolymers films (including one using oregano essential oil and citral), and this webzine article about an antimicrobial packaging made from orange pith.
Nanoparticles deserve a special mention, and not only for their use in antimicrobial packaging.
Nanotechnology mainly comprises of fabrication, characterization and manipulation of nano-range (<100 nm) molecules.
The application of nanotechnology in polymers involve the design, manufacturing, processing and application of polymer materials filled with nano-particles and/or devices of nano range.
Introduction of nanotechnology in food packaging sector has significantly addressed the food quality, safety and stability concerns.
Additionally, nanotechnology has been explored for controlled release of preservatives/antimicrobials, extending the product shelf life within the package.
Clay particles prevent gases from going directly through the polymer, forcing it to deviate from a straight path (tortuosity), therefore increasing resistance to gases and water vapor permeability. They also improve the mechanical properties even in biopolymers.
Nano sized clay particles (mainly montmorillonite) have been used to improve the mechanical and barrier properties of polymers (specially polyamides) since the 90’s (Kojima, Y., Usuki, A., Kawasumi, M., Okada, A., Fukushima, Y., Kurauchi, T., Kamigaito, O.,Mechanical properties of nylon 6-clay hybrid. J. Mater. Res. 8, 1185–1189).
It was possible to extend the shelf life of a 28 gram weight PET bottle from 14 weeks to 21 weeks, using the standard N-MXD6 with a five percent barrier layer of M9 due to its high carbon dioxide barrier.
Here’s an example of synergy between a 3 layer PET Bottle PET with oxygen scavenger and passive CO2 barrier technology:
- Oxygen scavengers and passive barrier technology (1% Amosorb™) in the outer layers.
- Nylon MXD6 and nanoclay (Imperm®) in the central layer.
3 layer PET Bottle PET with oxygen scavenger and passive CO2 barrier technology. Source: Nanotechnology in Packaging by Prof. Anup K. Ghosh.
Nanotubes are very interesting nanostructures with different applications. Carbon nanotubes can increase the tensile strength/modulus of several polymers. CNTs exhibit antibacterial properties, attributed to their direct penetration through microbial cells. They are also used as a conductor in nanoscale projects
Silver compounds are widely established as antimicrobial agents. it has the property of binding to the bacterial DNA, resulting into bacteriostatic effects.
Ag nanoparticles also affect the cytoplasmic membranes ando inhibit the respiratory chain enzymes. Silver zeolites are also used to create antibacterial polymer composites.
These nanoparticles can be combined with both edible and non-degradable polymers to develop active food packaging.
Recently, a team of researchers at the Indian Institute of Technology (IIT) Hyderabad used silver nanoparticles with bacterial cellulose to develop an advanced food packaging material.
Some other examples for Silver Based Antimicrobial Films for Coating and Food Packaging Applications
in this doctoral thesis.
TiO2 is being highly explored in preparing several. The antibacterial properties of TiO2 is well however, the antibacterial capacity of nano-TiO2 particles confined to the exposure of UV radiation.
There has been some concern to TiO2 nanoparticles, and France has announced the possibility of banning them in food products by 2020.
Here’s an example of from chitosan-titanium dioxide nanocomposite film to extend the storage life of tomatoes.
Regarding chitosan, let’s pause a moment to review some of its uses in active packaging.
Chitosan is a functional natural polymer that is non-toxic, biodegradable, has antimicrobial properties and is the most abundant carbohydrate in nature after cellulose.
It is obtained from chitin, which occurs inherently the cuticle of arthropods and endoskeletons of cephalopods. Because of inherent antimicrobial activity and good film forming ability of chitosan, it has a potential to be used in biodegradable active films.
Most of the review papers related to chitosan-based films are focusing on antibacterial food packaging films, or some combination with nanotechnology and polymer science.
To name few research projects and examples of chitosan in food active packaging:
- Chitosan used in edible coatings for blueberries
- Chitosan-based composite film fortified with grapefruit seed extract (GFSE) to double the shelf-life of perishable food,
- The n-CHITOPACK project for biodegradable packaging made of chitin and chitosan that will improve and conserve food products.
- Chitosan/montmorillonite coated paperboard with increased adhesion and barrier properties.
- Chitosan/nano ZnO composite films: Enhanced mechanical, antimicrobial and dielectric properties.
- Mahua oil-based polyurethane/chitosan/nano ZnO composite films for biodegradable food packaging applications.
Before moving on to Controlled Release Packaging, here’s a table summarizing the most important types Active Packaging commented on in this post and the previous one:
Controlled Release Packaging
Controlled Release Packaging (CRP) is defined as a new generation of packaging materials that can release active compounds such as antimicrobials and antioxidants at desirable rates to extend the shelf life of food products.
CRP aim is not only to prolong duration of active compound delivery, but also to the predictability and reproducibility of release rates.
Several examples of Antimicrobial Release Packaging were commented on the first section.
Here’s the typical structure of an antimicrobial multi-layer active film: outer layer, barrier layer, matrix layer, and control layer.
Oxidation of fats is one of the most important mechanisms leading to food spoilage, after the growth of microorganisms. The oxidation of lipids in food leads to a reduction in shelf-life due to changes in taste and/or odor, deterioration of the texture and functionality of meats, and a reduction in nutritional quality.
Oxidation of food can be avoided by use of oxygen scavengers and antioxidant agents in the packaging. Also, oxidation can be avoided by eliminating radicals (mainly oxo, hydroxyl, and superoxide) as soon as they are formed.
The cereal industry currently uses the antioxidants BHA or BHT by incorporating these additives into a wax liner.
Increasing concern with the use of synthetic chemicals has led to the use of natural antioxidants. Packaging researchers have incorporated α-tocopherol (vitamin E) into a heat seal layer of Surlyn/EVA® coextruded with an HDPE.
An alternative (as in the case of antimicrobials ) is to use varnishes or coatings that incorporate natural essential oils or extracts such as rosemary extract, which acts as a radical scavenger either in the vapor phase or by direct contact.
Flavors and Aromas
The incorporation of food aromas into the polymer material can be used to attract consumers when the package is opened, and also to balance any detrimental effects of aroma/flavor loss. Plastics absorb/release substances that affect aroma depending on several factors regarding both polymers and aroma chemical structure.
Commonly used polymers for the release of aromas are PE, PP, ethylene vinyl acetate (EVA), ionomer, nylon, polyester, and polyvinyl chloride.
Encapsulated flavors can be added directly into packaging materials at the time of manufacturing.
In 2013 PepsiCo filed the patent application for their ‘aroma delivery system’ consisting of gelatin capsules that release aroma compounds when the bottle is opened.
The Spanish Technological Institute of Packaging, Transport and Logistics (Itene) is working on the Actiaroma project using encapsulating compounds to include flavors in packaging materials.
CRP can also be used to release other substances that limit the shelf-life of the product (such as vitamins or other active principles), avoiding the addition of excess quantities and reducing production costs.
That’s all for now, maybe I will write a post about MAP in the near future.
March 2019, Bruno Rey – The Packaging Blog –