How is smart packaging smart?

Intelligent packaging is an extension of active packaging. While active packaging is designed to take action in order to extend the shelf life of a product — such as releasing or absorbing substances, thereby extending the duration of high quality for any given product — intelligent packaging goes further. Here, the purpose of the design is to monitor the condition of the product and to communicate to the consumer any changes in the product.

Intelligent packaging should provide more reliable information than just the expiry date printed on the packaging. It should monitor certain aspects of a food product (for example, shelf life) and report information to the consumer. Some of the chief purposes of the intelligent packaging system are to improve the quality or value of a product, to provide more convenience or to provide tamper or theft resistance to the pack.

There are currently three major types of intelligent packaging technologies employed:

• Sensors (biosensors, gas sensors).
• Indicators (temperature, freshness).
• Data carriers (barcode, radiofrequency identification or RFID).

There is a great variety of indicators used in each of these types, which shows great opportunities for developments.

As an example, time-temperature indicators (TTIs), one of the commonly used indicators, can be classified as:

• biological
• physicochemical
• chemical
• enzymatic
• diffusion-based
• polymer-based.

Time-temperature indicators

Diffusion

Based on Fick’s law, diffusion-based TTIs are widely used. The diffusion rate of a liquid material is higher at higher temperatures and the extent of diffusion shows the total influence of environmental temperature.

Chemical

The applied principle of chemical TTI is a temperature-dependent chemical reaction. This type of TTI includes polymerisation-based, photochromic-based redox reaction-based TTI depending on the different reactions utilised.

Biological

This relates to biological reactions referring to enzymes or microorganisms. Enzyme-based indicators present colour change caused by the reaction between enzymes and substrate with a pH change. One part includes lipolytic enzyme solution, lipase and a dye with pH indication. The other part is a substrate, predominantly triglyceride. The indicator will be activated when the gap between enzyme and substrate is broken so that two parts are mixed.

Photochemical

This type of intelligent packaging contains thermochromic ink consisting of dye, reagent and solvent. UV light activates the indicator because the ink absorbs photons with certain wavelengths, and activates them to excited states and forms free radicals or ions.

Controlled permeability packaging

A less expensive alternative to modified atmosphere packaging (MAP) is controlled permeability packaging (CPP). In this type of packaging, no gas is flushed out or injected, but rather the produce is packaged within a film that controls the quantity of O₂ and CO₂ flowing into and out of the package. This type of packaging is suitable for small-scale suppliers in developing countries, where pure MAP might result in the product cost being too high for the average consumer. This packaging produces shelf-life results close to, but not as high as pure.

Controlled permeability packaging could be the solution to food waste, especially in developing countries where suppliers might not be able to afford pure modified atmosphere packaging machinery and processes, and also where the average consumer might not be able to afford modified atmosphere packaged produce.

Nanotechnology

Nanotechnology is a form of active packaging that utilises bio-nanocomposites consisting of nanoparticles embedded into a biopolymer matrix — with dimensions less than 100 nm.

Antimicrobial nanoparticles

Antimicrobial action of silver nanoparticles

The antimicrobial action of silver nanoparticles is attributable to their high surface area-to-volume ratios which favour their interactions with microbial cells. These silver nanoparticles cause direct damage to the cell membranes of harmful microorganisms by interacting with negatively charged biomacromolecular compounds with disulfide or sulfhydryl groups and nucleic acids. This results in cell membrane deformation, inactivation of metabolic processes and cell death.

Barrier properties of nanoclay

Nanoclays consist of montmorillonite silicate layers also known as nanoplatelets which are in a stacked arrangement with a nanometric thickness of 1 nm and a structural dimension of 100 nm.

These nanoclays are incorporated into the matrices of a polymer to delay the flow of gases such as O₂ and CO₂ from the external environment to the internal environment. Nanoclays exhibit excellent barrier properties due to their high rigidity, aspect ratio and affinity as a result of the interfacial interaction between the matrices of the polymer and the dispersed nanoclay.

Nanosensors

Nanosensors as microorganism detectors

Nanosensors are excellent microorganism detectors as they are able to monitor the safety and quality of food products at various stages of the food supply chain. These sensor systems have the ability to accurately detect food spoilage or microbial contamination in food by interacting with the external and/or internal environment of the food, thus producing a response in the form of a visual signal such as colour indicators on nanosensor labels which correlate with the current state of the food product.

Active and intelligent packaging are the ultimate aspects that extend food shelf life, enhance quality, ensure safety and monitor or acquire information regarding product performance through the supply chain. Nanotechnology has the potential to be the next ‘big thing’ in the science of smart packaging.

Prof Pierre Pienaar MSc, FAIP, CPP, Education Director – AIP, Vice President Education – WPO.

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