Active and intelligent packaging for food: Is it the future?

Transcription

1 Food Additives and Contaminants, October 2005; 22(10): Active and intelligent packaging for food: Is it the future? A. R. DE JONG, H. BOUMANS, T. SLAGHEK, J. VAN VEEN, R. RIJK, & M. VAN ZANDVOORT TNO Quality of Life, Zeist, The Netherlands Abstract This paper gives an overview of the legal consequences of a new EU framework regulation on food contact materials which includes controls on active and intelligent packaging. Recent developments in active and intelligent packaging systems are described, two examples of which aim at achieving improvements in quality and safety of food products. The first one is an on-command preservative-releasing packaging system. The second system is an intelligent concept, based on the development of a non-invasive microbial growth sensor to monitor the sterility of food products. Keywords: Intelligent, active packaging, food packaging, non-invasive, spoilage indicator, food contact materials legislation Introduction Active and intelligent packaging systems can provide several benefits to the quality and safety of food. The active systems aim shelf-life extension of the food products by keeping its quality for longer (e.g. oxygen absorbers in nuts to prevent rancidity, caused by fat-oxidation). The intelligent systems are aiming to monitor the quality of the food product or its surrounding environment to predict or measure the safe shelf-life better than a bestbefore-date. A European Commission funded project (FAIR-project CT ) known by the acronym of ACTIPAK came up with recommendations which were taken up in the drafting of amendments to the EU Framework Directive for food contact materials 89/109/EEC. This resulted in the adoption of a new Framework Regulation (1935/ 2004/EC) in which the use of active and intelligent packaging systems are now included. The new Regulation will authorize the use of active and intelligent packaging, provided the packaging can be shown to enhance the safety, quality and shelf-life of the packaged foods. The new Framework Regulation for Food Contact Materials (1935/2004/ EC, which was published on 27 October 2004) is a Regulation instead of a Directive, which means that it will become valid immediately in all EU Member States. All active and intelligent packaging systems are also subject to pre-existing food contact material (FCM) regulations, e.g. plastics, ceramics, etc. In addition, some of the systems may also be subject to regulations on food additives, biocides, labelling, environment/waste, modified atmosphere, food hygiene, safety, weight and volume control (a gas absorber or releaser can theoretically influence the volume of a packed food product). All new active and intelligent packaging systems initially need to be evaluated by the European Food Safety Authority (EFSA). Based on the outcome of that evaluation, the Commission (DG SANCO) will grant a petitioner, authorization for the submitted active and intelligent ingredients/systems, which will be entered in the Regulation. The general requirements for food contact materials (1935/2004/EC) also applies to active and intelligent packaging systems and, consequently, they shall not endanger human health. Releasing systems are however allowed to change the composition of the food, provided the released substance is an authorized food additive. Labelling should comply with the food additive Directive. The release or absorption of substances should not mislead the consumer. Antimicrobial components incorporated in FCMs and articles intended to be released into the food (directly or via the headspace) must be approved Correspondence: A. R. de Jong. dejong@voeding.tno.nl ISSN X print/issn online ß 2005 Taylor & Francis DOI: /

2 976 A. R. de Jong et al. food additives and will need evidence of their effectiveness. Any claim which is made for the active system should be proven. Preservatives may also be added to FCMs in order to obtain an anti-microbial surface. These applications are not considered active materials. These systems should not release the preservative into the food and thus have no effect on the microbial conditions of the food. If the material is a plastic, it must comply with the current framework Regulation (1935/2004/EC) and the Directives on plastics (2002/72/EC). New active anti-microbial system for food packaging: Release on command Some new developments in active packaging have included preservative-releasing packaging systems aimed at extending the shelf-life of the packed food and thereby maintaining high quality. Such a preservative-releasing packaging system called the BioSwitch concept has recently been developed and patented (Thijssen et al. 2003, 2004). This system only releases its preservative on command, which means that a preservative will be released from the packaging material if bacterial growth occurs, thus inhibiting growth of the emerging bacteria. The advantage of such a system is that the anti-microbial agent only comes into contact with the food matrix when there is microbial growth, so lower levels of preservatives can be used in the food itself. Another advantage is that the preservative can be made highly selective to inhibit spoilage organisms without, for example, inhibiting a desired fermentation process. This system is under development in such a way that it will be, also from a legislation point of view, applicable under the new European legislation for active packaging. The general concept of BioSwitch is shown in Figure 1, which illustrates a system that is able to detect changes (external stimulus) in the environment and to respond to them automatically. For instance, the external stimulus may be a change in temperature, ph, humidity, UV, or the presence of certain metabolites. The stimulus is converted into a certain functionality. The goal of this general concept is to develop systems that are active only at a specific time and place, i.e. when and where required. The general advantages of the concept are, for example, increased stability and specificity and/or reduction in the chemicals needed. An application of BioSwitch is that of an anti-microbial active packaging (see Figure 2). Small particles consisting of a matrix of polysaccharides such as starch or blends of different natural polymers containing an anti-microbial compound are coated onto a food packaging surface. In the case of initial microbial contamination, these micro-organisms will start to secrete enzymes, which will hydrolyze the polysaccharides (matrix) in order to use these as substrate. Partial degradation of the particles will induce release of the anti-microbial compound, resulting in inhibition of microbial growth. In this particular case, particles consisting of modified starch were developed. These particles are capable of absorbing an amount of water corresponding to times their own weight. These particles were used to absorb lysozyme, a natural anti-microbial compound isolated from chicken egg. To enable absorption of lysozyme, external stimulus sensor BioSwitch response Figure 1. General concept of BioSwitch. Functionality Figure 2. Schematic representation of anti-microbial active-packaging. Micro-organisms hydrolyze starch-based particles, causing release of the antimicrobial lysozyme, resulting in inhibition of microbial growth.

3 Active and intelligent packaging for food 977 a starch gel with a suitable porosity was developed by varying the degree of cross-linking and introducing negatively charged groups. These groups were also needed for strong binding of lysozyme, resulting in a no-release situation. The charged groups were introduced with an oxidation method that allows accurate adjustment of the degree of oxidation and thus a good balance between binding capacity and biodegradability. Knowledge of the synthesis parameters like choice of biopolymer or amount and kind of introduced charge and cross-linker provide a good basis for the tailor-made development of specific BioSwitch particles for a specific application. The evaluation of Bioswitch involved examining whether lysozyme could be released in vitro by adding amylase to a suspension of starch-based particles. Figure 3 shows that, under normal conditions, the particles do not release any lysozyme a so-called no-release situation Lysozyme activity Time (minutes) amylase Figure 3. Release of lysozyme from particles upon addition of amylase. Figure 4. Inhibition of growth of B. licheniformis in vicinity of particles containing lysozyme. On addition of amylase, a rapid induced release of lysozyme is observed. To test whether particles containing lysozyme are also effective in inhibiting bacterial growth, particles were spotted into the centre of an agar plate containing Bacillus licheniformis. A growth inhibition zone surrounding the spot was visible, showing that growth of B. licheniformis is strongly inhibited by the particles (see Figure 4). Intelligent systems in the food packaging chain (De Jong and Van Zandvoort 2004) In the EU, intelligent packaging systems are defined as Packaging that monitors the internal and/or external conditions of a product through its life cycle, in other words, a package that can communicate (i.e. indicate) the quality of the product (TNO nutrition & Food Research et al. (2002) Basically, there are two types of intelligent packaging: One based on measuring the condition of the package on the outside, the other measuring directly the quality of the food product, i.e. inside the packaging. In the latter case there is direct contact with the food or with the headspace and there is always the need for a marker indicative of the quality and/or safety of the packed food. The following indicators can be distinguished: Time-temperature indicators (TTI). The basic idea behind temperature-related food quality indicators is that the quality of food deteriorates more rapidly at higher temperature, and thus maintaining correct low storage temperatures ensures food safety. TTIs are placed at the outside of each single package or can be placed in bigger containers or trays. A TTI can be defined as a small measuring device that shows a time- and temperature-dependent, irreversible change (e.g. a colour change). It is important that the run-out time of the indicator correlates well with the shelf-life-limiting factor of the food. Gas leakage indicators. Oxygen and carbon dioxide indicators can also be used to monitor food quality. They can be used as a leakage indicator or to verify the efficiency of, for example, an oxygen scavenger. Most of these indicators are based on colour change as a result of a chemical or enzymatic reaction. These indicators have to be in contact with the gaseous environment inside the package and hence are in direct contact with the food. An example of a noninvasive oxygen sensor in a package monitored in production lines is the fluorescent technology developed by TNO and currently marketed by OxySense Inc. Toxin indicators. The key problem for toxin indicators is that pathogenic micro-organisms generally

4 978 A. R. de Jong et al. only exist in or on a food product at very low concentrations (but already can be dangerous at those levels) and are not homogeneously distributed throughout the whole food. For this reason it is not very likely that a marker for a toxin (or a toxin-producing organism) is present at high levels; thus, a detector or sensor has to be extremely sensitive and completely in contact with the food. These systems are not likely to become available in the near future. Spoilage detectors/freshness indicators. An ideal indicator for the quality of packaged foods would indicate real spoilage or lack of freshness of the product instead of just temperature abuse or package leaks. In this way the starting quality of the product would be taken into account as well as all supply chain mistakes. Spoilage detectors are sensitive to specific by-products originating from deterioration reactions in the food and are therefore placed inside the package. They have to be thoroughly validated for every type of the food product. Nearly all of them are still in a developmental stage at universities or innovative companies. A good example of such an indicator for a specific product is an indicator for the freshness of packed fish products based on either the tri-methyl amine formed by the bacterial reduction of tri-methylamine N-oxide (TMAO) or the total volatile base (sum of basic reduced nitrogen gases). An example of a non-specific indicator is the microbial growth indicator under development and patented by TNO (Van Veen 2004). This is actually a non-invasive microbial growth indicator that is able to determine the presence of micro-organisms in closed, aseptic containers. For several applications dealing with packed products in closed, aseptic containers, there is a need to determine whether or not a container is contaminated with microorganisms without opening the container. For instance, in case of sterile (tissue) cultures of plants, there is a need for an indicator to confirm sterility of the contents of a container before use. In the project description (Van Veen 2004) a proofof-principle of the concept for sterile tissue culture of plants is given. The concept is based on the idea of inducing extracellular enzymes by means of substrate addition (optional) to the medium used in a particular application in combination with a noninvasive sensor detecting either directly extracellular enzyme activity or the metabolic products (see Figure 5). An accumulative detection principle is applied to enable the detection of low levels of initial contamination even after the micro-organisms have died. The detection strategy is mainly based on fluorescence detection although for visual detection also colour-based indicators are used. It was concluded that the combination of certain protein additions and the detection of protease activity was the most successful combination in case of sterile plant cultivation. The best results have been obtained with an accumulative detection principle, enabling not only the detection of low levels of initial contamination but also being effective after the logarithmic growth phase of the micro-organisms. Enzyme activity sensors based on fluorescence with a high emission wavelength are regarded as the right choice for further development in order to decrease matrix effects. A number of possibilities to achieve this have been investigated and its feasibility has been demonstrated (see Figure 6). Either the enzyme activity or the products formed will cause an optical change in the fluorescent properties of these sensors, which can be detected non-invasively from the outside of the container. These sensors are insensitive to ph. The sensors could be applied as Figure 5. Demonstrators in two different containers using different indicators.

5 Active and intelligent packaging for food 979 Accumulative protease activity (a.u.) E. Coli L.B. Plantarum A. Niger Days Figure 6. Measured accumulative protease activities in a closed container at room temperature for various micro-organisms. a sticker or printed onto the container or the packaging material. Besides the application of sterile plant cultivation, a number of other applications or markets are identified for the technology developed in this project. The markets for non-invasive sensors that safeguard sterility issues in clinical tissue culture applications, in sterile food products (e.g. clinical food, baby food) and for microbiological ingress measurements are regarded as the most promising ones. For these other applications, possibly other designs can be applied, for instance generic detection of amylase activity. Advantages of this technology are: It is non-invasive, so it can be applied in any container; it will be cost-effective (for the disposable part costs are in the order of euro cents); it is generic with respect to the detection of microbiological contamination; there will be no need for antibiotics; it is compatible with flexible packaging materials and disposable tissue culture products; and it can add functionality to existing products or packaging. 2. Reliability and effectiveness: Active systems must be thoroughly validated for each specific application to be sure that they are dedicated and effective. In case the shelf-life date would be replaced by the indicator, the performance of the indicator would need to be 100% effective, giving a guarantee for a zero false-positive result. 3. Technical hurdles: For active systems incorporation of the active component with sufficient capacity in the main material is needed. The main technical hurdle for intelligent systems is in the development of interactive freshness indicators, which measure directly the level of (microbiological) contamination of the product or other parameters that are indicative of the product s quality level. 4. Costs for both types are still high. It is obvious, that these costs will drastically be reduced with broader application and thus scaling-up of production. Discussions are ongoing as to whether consumers will be ready to pay the extra costs for the extra safety/quality tools. 5. Food producer, consumer and retail acceptance will be needed to enable an introduction on a large scale. In the ACTIPAK project, consumers attitudes were investigated in a number of European countries, showing that most consumers are open to innovations in this area provided the material is safe and the information is unambiguous for the user. Despite the hurdles that have to be overcome in the near future, there is a strong view that active and intelligent packaging will be a technical tool in the market with a high potential, covering both more transparent communication to consumers and the need for the retail and food industry to better control the food production chain. Future perspectives for active and intelligent packaging A bright future may be anticipated for active and intelligent packaging, as it fits perfectly with the food safety strategy, involving an improved level of food safety and transparency to consumers. For the future development in Europe some major factors have to be considered: 1. Some legal hurdles: Most active and intelligent concepts that are on the market in the USA and Australia cannot be introduced in Europe yet, due to more stringent EU legislation. References De Jong AR, Van Zandvoort MMJ From best before date to freshness indicator? Food and Beverage International September 2004: Thijssen HMWM, Montijn RC, Timmermans JW Antimicrobial envelopes. Patent number WO Thijssen HMWM, Montijn RC, Timmermans JW Inducible release vehicles. Patent number WO TNO Nutrition & Food Research et al European project FAIR R&D program (CT ) ACTIPAK, Evaluating safety, effectiveness, economic-environmental impact and consumer acceptance of active and intelligent packaging. Van Veen JJF Method for the non-invasive detection of microorganisms in a closed container. Patent number WO