Dr. Nyi-Nyi Htun
KU Leuven, Belgium
Due to the increasing demand towards sustainable productions that calls for ensuring the safety and quality of food and reducing incident risks and environmental impact, contemporary food business organisations have begun to focus on the possibilities to expand the shelf life of perishable food products by reducing the demand for additives and preservatives, and at the same time considering changes in quality. To this end, smart packaging systems which utilise technologies, for example oxygen scavengers, antimicrobial agents, sensors and status indicators, have emerged (Realini and Marcos 2014).
While traditional packaging focused on the use of inert materials which comes in contact with food, smart packaging systems are based on the useful interaction between packaging environment and the food to provide active protection to the food and a better understanding of product condition for consumers (Biji et al. 2015). Smart packaging systems involve two concepts: active and intelligent packaging (Biji et al. 2015; Vanderroost et al. 2014). The following figure shows a framework proposed by Yam et al. (Yam, Takhistov, and Miltz 2005) which encapsulates various packaging technologies.
Fundamentally, active packaging aims to achieve better protection of the product whereas intelligent packaging to achieve better communication with consumers. Intelligent packages allow monitoring the quality/safety condition of a food product and can provide early warning to the consumer or food manufacturer, whereas active packages release a type of substance such as an antimicrobial or antioxidant within the package to protect the food product. Typically, intelligent packaging systems contain smart devices which are small, inexpensive labels or tags that are capable of acquiring, storing, and transferring information about the functions and properties of the packaged food (Fang et al. 2017).
This article presents an overview of available technologies in intelligent packaging by synthesing a number of existing research papers (Biji et al. 2015; Chowdhury and Morey 2019; Fang et al. 2017; Ghaani et al. 2016; Kuswandi et al. 2011; Lloyd, Mirosa, and Birch 2018; Mohebi and Marquez 2015; Müller and Schmid 2019; Singh et al. 2018; Vanderroost et al. 2014). To begin with, intelligent packaging includes 3 distinct technologies; these are indicators, sensors and data carriers. The following table (curated from (Fang et al. 2017; Mohebi and Marquez 2015; Pavelková 2013) highlights an overview of indicators, sensors and data carriers that are being used in the domain of intelligent packaging.
|Time-temperatures indicators||Mechanical, chemical, enzymatic||Storage conditions||Foods stored under chilled and frozen conditions||Easy to integrate, can be checked by naked eye, cheap and economical, can be measured by electronic devices||No information about quality of food, must be conditioned before use, no contact with food|
|Freshness indicators (e.g. microbial growth)||pH dyes, all dyes reacting with certain metabolites||Microbial quality of food (i.e. spoilage)||Perishable foods such as meat, fish and poultry||Sensitive, can be checked by naked eye, cheap and economical, can be measured by electronic devices||Prone to false negatives results, may interfere in food quality|
|Gas indicators||Redox dyes, pH dyes, enzymes||Storage conditions, package leak||Foods stored in packages with required gas composition||Can be integrated into the packaging films, can be checked by naked eye, cheap and economical, can be measured by electronic devices||No information about gas concentration, chemical dye may interfere in food quality|
|Biosensor (e.g. pathogen)||Various chemical and immunochemical methods reacting with toxins||Specific pathogenic bacteria such as Escherichia coli O:157||Perishable foods such as meat, fish and poultry||Can be integrated into the packaging films, can be checked by naked eye, cheap and economical, can be measured by electronic devices, pathogen and microbial detection||Cannot detect low concentrated contamination, may have chemical effect on the food|
|Gas sensors||Metal oxide semiconductor field-effect transistors (MOSFETs), piezo-electric crystal sensors, amperometric oxygen sensors, organic conducting polymers, and potentiometric carbon dioxide sensors||Concentration of carbon dioxide, oxygen, hydrogen sulphide||Perishable foods such as meat, fish and poultry||Sensitive, can be integrated into the packaging films, high spatial resolution, can be checked by naked eye and optical devices, not affected by heat, electromagnetic and stirring||Fouling of sensor membranes, cross-sensitivity to carbon dioxide and hydrogen sulphide, consumption of the analyte (e.g., oxygen)|
|Barcodes||Symbology||Product and manufacturer information||Product identification, facilitating inventory control, stock reordering, and checkout||Fast, cheap, easy to print||Requires line of sight|
|RFID tags||Radio waves||Product and manufacturer information||Product identification, supply chain management, asset tracking, security control||Accurate, fast, can be printed into barcodes.||The signal can be lost due to interference, printed tags can be expensive.|
Indicators are devices that convey information associated with the presence or absence of a substance, the amount of the substance, or the degree of interaction between two or more substances (Chowdhury and Morey 2019). Typically, such information is displayed to consumers through visual changes, for example, different colour intensities or the diffusion of a dye along a straight path (Biji et al. 2015). Literature has highlighted three different types of indicators: time temperature indicators, freshness indicators and gas indicators (Biji et al. 2015; Chowdhury and Morey 2019; Müller and Schmid 2019).
Time Temperature Indicators
Time temperature indicators (TTIs) can be placed in individual or bulk packages to convey time-temperature history of a product (Chowdhury and Morey 2019). They are particularly useful to warn consumers of temperature abuse for chilled or frozen food products (Pavelková 2013). A subcategory of TTIs known as thermochromic ink uses a type of functional ink that changes colour with exposure to different temperatures (Vanderroost et al. 2014). By definition, function inks are printable inks that react to environmental changes with colour change (Glicoric et al. 2019). Other examples of functional ink include photochromic inks that change their colour when the intensity of incoming light changes, invisible fluorescent inks that can be seen under UV or IR light, phosphorescent inks that glow in the dark after exposure to a source of light, hydrochromic inks that change colour after contact with water, and touch’n smell inks that release aroma when rubbed with a finger, among others (TagItSmart, 2017).
Freshness indicators provide direct product quality information resulting from microbial growth or chemical changes within a food product (Chowdhury and Morey 2019). Certain metabolites that are targeted in detecting freshness are organic acids, ethanol, volatile nitrogen, biogenic amines, carbon dioxide, glucose, and sulfuric compounds (Kerry, O’Grady, and Hogan 2006). Freshness is determined through reactions between indicators included within the package and said compounds (Ghaani et al. 2016).
Gas indicators can monitor changes in the inside atmosphere of a package due to microorganism metabolism and enzymatic or chemical reactions on the food (Ghaani et al. 2016). Oxygen and carbon dioxide concentrations are most commonly captured by gas indicators (Müller and Schmid 2019) since their concentration is strongly correlated with spoilage (Meng et al. 2014). Gas indicators often use redox dyes, a reducing compound and an alkaline compound to indicate the concentration (Ghaani et al. 2016).
Sensors are used to detect a wider range of chemicals inside food packages with greater functionalities. They can detect and respond to some type of input from the physical environment, and the output is generally a signal that is converted to a human-readable display. Unlike indicators which can display the state of a product in the package, sensors are often monitored by an external device (Kerry et al. 2006). Sensors commonly found in literature are biosensors are gas sensors.
Biosensors are used to detect, record and transmit information pertaining to biological reactions of food products (Biji et al. 2015). They contain a bioreceptor that recognises elements such as enzymes, antigens, hormones, nucleic acids, etc. and a transducer which uses optical amperometry, acoustic and electrochemical sensors, connected to data acquisition and processing system (Chowdhury and Morey 2019).
Gas sensors are used for detecting the presence of gaseous analyte in the package, such as oxygen, carbon dioxide, water vapour, ethanol, hydrogen sulphide, etc. (Biji et al. 2015). As the spoilage status of a food product can be determined by monitoring the concentration of certain gases, like carbon dioxide or hydrogen sulphide (Müller and Schmid 2019), gas sensors in food packaging often focus on monitoring such gases.
Data carriers are used as a medium to support traceability of products. Radiofrequency identification (RFID) and barcode are the most common forms of data carrier used in this domain (Robertson 2016). They make the information flow within the food supply chain more efficient by supporting automatization and traceability. Smartphones nowadays are capable of reading most RFID tags and barcodes which makes them the most ideal starting point to enhance communication with consumers.
RFID uses electromagnetic fields to automatically identify and track tags attached to objects. They are the most advanced example of a data carrier (Ghaani et al. 2016). An RFID system includes three main elements: 1) a tag formed by a microchip connected to a tiny antenna, 2) a reader that emits radio signals and receives answers from the tag in return and 3) a middleware (i.e. a network connection, web server, etc.) that bridges the RFID hardware and enterprise applications (Ghaani et al. 2016). With recent breakthroughs in the domain of printed electronics, RFID tags can be printed on flexible substrates such as polyimide, PEEK, PET, transparent conductive polyester, steel and even paper using electrically functional inks (Vanderroost et al. 2014).
Barcodes are the most basic form of data carrier in intelligent packaging. They have been used in food packaging since 1970 to accelerate inventory control, stock reordering and checkout of products (Manthou and Vlachopoulou 2001). Although barcodes traditionally do not provide any kind of information on the quality status of food, a number of previous work has explored the possibilities of using thermochromic ink to print barcodes (Ghaani et al. 2016; Vanderroost et al. 2014), or combining environmental sensitive areas with 2-dimensional barcodes (aka QR codes) (Gligoric et al. 2019).
This article presents an overview of the state of the arts in intelligent packaging technology. In general, there are three main components in intelligent packaging technology: indicator, sensor and data carrier. Some of the most popular sub-components of the three main components include time temperature indicator, freshness indicator, gas indicator, biosensor, gas sensor, RFID and barcode. Quite a number of research work has already identified a great number of commercially available smart packaging technologies that are inexpensive (Biji et al. 2015; Chowdhury and Morey 2019; Fang et al. 2017; Ghaani et al. 2016; Kuswandi et al. 2011; Lloyd et al. 2018; Mohebi and Marquez 2015; Müller and Schmid 2019; Singh et al. 2018; Vanderroost et al. 2014). Despite this, we have not yet seen the majority of said technologies being used widely. Research has suggested that end-user acceptance and trust towards a given technology have a strong influence on their adoption of the technology (Suh and Han 2002; Wu et al. 2011). In the next article, we will look at the barriers and enablers influencing the adoption of intelligent packaging technologies from end-user point of view.
Cover Photo: Shutterstock
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