Víctor M. Mocholí Alabau, Packaging Area - Chemical Laboratory of AIMPLAS, and Lorena Rodríguez Garrido, Functional Printing and Coatings department of AIMPLAS explore the development of active packaging in technical paper.
The development of new packages and packaging technologies for fresh fruits and vegetables is a constant for packaging companies, in order to give an answer to the fresh products growing demands of consumers.
One of the keys in the development of active packaging for fresh products is to identify the food degradation mechanisms and act on them in order to reduce or delay these processes and thus increasing the shelf life of the product. In the case of fresh fruits, one of the critical points is acting on ethylene, produced in the fruit’s ripening process. Besides, its presence speeds up the degradation process.
Ethylene, a plant hormone produced during the ripening of fruits and vegetables, is the responsible for the modifications of the respiration rate, tissue softening and other physiological disorders, thus accelerating the senescence of fruits and vegetables.
Over time, different methods to reduce the negative effects of ethylene on agricultural products have been studied. Currently, there are a great number of technologies and procedures meeting that purpose: including low-temperature storage, modified and controlled atmospheres, and the implementation of growth promoters such as auxins and gibberellic acid and calcium, among others. However, thanks to its efficiency, ripening chemical retardants have been used successfully in pre and post-harvest.
By its mode of action, chemical retardants can be classified in:
- Ethylene synthesis inhibitors
- Ethylene action inhibitors
- Ethylene oxidants responsible for removing it from the environment
At packaging level, there are different solutions of ethylene scavengers that can be applied on the fresh fruit packaging, by means of different forms of application both in flexible and rigid packaging, either incorporated in mass in sachets inside the packaging or as coatings in the packaging
Commercial solutions of ethylene scavengers
There are market solutions that use the above mentioned chemical retardants, incorporating them into the packaging materials, solutions that can be found at commercial level. Most of these solutions intended to remove the packaging’s ethylene can be found as sachets inside the packaging, with a limited acceptance by the consumer, and to a lesser extent, in solutions integrated directly in packaged material, solutions that are growing in popularity.
The objective of these solutions is to extend the shelf life of packaged fresh products due to the adsorption of ethylene by the dispersed compounds integrated into plastic. For that purpose, shelf life tests are performed to compare common materials with materials with scavenger compounds on its matrix. Such evidence shows generally an extension of the shelf life or a reduction of ethylene in the packaging’s headspace. However, when incorporating the ripening retardant compounds, other variables can be introduced such as the modification of the film permeability that can also affect the shelf life of the product. For this reason, it is important to know all the variables that affect the packaging and have a global overview to provide a suitable solution. In this sense, AIMPLAS has an extensive experience in the development of active packaging, in assessing and helping to the development of customized solutions based on both commercial products and new developments.
Incorporation mechanisms of ethylene scavengers in packages
As mentioned above, there are different mechanisms of action to reduce or eliminate ethylene from packages and thus extend the ripening process and, therefore, the shelf life of fruit. If we talk about solutions on direct food contact, we must keep in mind that we could not work with oxidant compounds and thus we will work the inhibition of ethylene’s action, as well as its ethylene synthesis and its action.
For that purpose, we work with ethylene scavenger compounds, whose aim is to eliminate ethylene from the environment of fresh fruits and vegetables, slowing down the ripening processes and the deterioration of vegetable products, extending the shelf life of fruits and vegetables.
Currently, there are two mechanisms to insert these compounds on the packages: they can be introduced into the polymeric matrix (mass), or they can be applied as a coating (dispersion).
In many cases, the incorporation method depends on the type of packaging to be used for packing products, and the capacity of the company to incorporate the scavenger into its products.
The way to incorporate these materials into film, containers or packages is through its mass incorporation, by means of compounding, where a concentrate with the scavenging compound is created. Subsequently, this concentrate is processed by extrusion or injection to result in a packaging with the optimum scavenging concentration according to the need.
If the incorporation of the absorbent is by applying a coating, it will be necessary to work in dispersion, where the scavenger compound is dispersed in a polymeric matrix in solution, to result in the formation of a scavenger coating.
In order to apply this coating on the material or formed package, there are different techniques. We can use conventional printing techniques to apply this coating formulated on film or reel material. In order to not increase the cost of the product, this application is optimal when the material needs to be printed. However, if we have a formed packaging, then the application of the coating must be performed through packaging spraying.
Conclusions
Ethylene is the main ripening inducing agent of fruits and vegetables and may cause the premature ripening of some products, even ruin others.
In order to reduce the concentration of ethylene and extend the shelf life of horticultural products, solutions already existing in the market, whose only use limitation is related to the material to be used, whether it is approved for food contact have been developed.
If we want to use a scavenging compound for direct food contact, we must seek suitable solutions for this contact that are mainly limited to solutions inhibiting and reducing the ethylene concentration.
These compounds can be incorporated by two different mechanisms, depending on the converting company and the packaged fruit’s need. In this way, we can incorporate absorbers in the polymer’s mass in order to produce different scavenging packages.
In case of flexible packages intended to be printed, we will be able to assess the option of applying a coating with the absorbent in dispersion, and in case we have finished packages we will be able to apply also this scavenging coating by spraying.
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