Javier Osés Fernández, a chemist at the Public University of Navarre, says in his research paper on the subject that edible coatings could help packagers meet the demand from food companies for new packaging that can help prolong the shelf life of products, while being recyclable or biodegradable.
Currently, the three systems of conservation most used by the food industry are vacuum packing, nitrogen sweeping and aluminum foil. Protection is currently carried out with a mixture of synthetic chemical compounds that are not completely biodegradable.
Now packagers and researchers are exploring the use of edible coatings - transparent films that cover food items and act as a barrier to humidity and oxygen. Fernández research showed that such films can be used as a host for additives in the conservation of the properties of the product or simply in order to improve its appearance.
They can also help companies reduce the amount of plasticisers used to packaging foods.
To compare the performance of edible coatings to synthetic packaging, Fernández prepared a number of samples of whey protein isolate (WPI), of mesquite gum and of starch, and stored them for six months at different humidity levels.
His first conclusion from the study is that, depending on the type of plastifier used, the mechanical properties of the coating changes with the passage of time.
Thus, those films used with sorbitol plastifier underwent variation in their mechanical properties, such as flexibility; while those containing glycerol did not alter their composition.
Once he determined the ideal plastifier for the coating, Fernández observed that, in order to improve malleability, it was necessary to introduce a lot of glycerol.
However, using high quantities of plastifier in a coating results in an increase in its permeability to water vapour, limiting its usefulness. To counterbalance this deficiency, he incorporated mesquite gum into the milk serum protein. Mesquite gum is a polysaccharide that grows in dry and semi-arid regions of the north of Mexico.
The resulting mix is a compound film that is resistant and maintains suitable mechanical properties. Mesquite gum used as an edible coating of fruit is currently the best-known example of the application. However, it can also be efficacious for conserving foodstuffs that are high in polysaturated fatty acids, and are susceptible to oxidation. Such foods include nuts, meat and certain fish such as salmon.
"The use of mesquite gum is an economical and efficacious alternative with a promising future, not only for food conservation, but it could also become an economic resource for indigenous peoples, currently marginalized, as well as having the effect of reducing the desertisation of the soil," Fernández suggests.
He evaluated to what extent the edible films he had developed were able to protect fatty foods by testing them on sunflower oil. In a first stage, he carried out trials with WPI coatings.
His results showed that the protection capacity of the film depended on the amount of plastifier in the film, on its thickness and on the relative humidity of storage of the foodstuff.
The most efficient WPI films were those of greater thickness, with less amount of plastifier and that had been exposed to low relative humidity, the concluded.
The second stage of the project involved a similar experiment, but with films made of starch, known to be an efficient barrier to oxygen. In this case, the thickness of the film did not influence the protector effect on the oil. The experiment showed that starch films are more effective for packaging products with a high relative humidity.
Fernández then examined the application of edible coatings with WPI on chicken breasts. He also incorporate nisine, an antioxidant agent that penetrates the foodstuff little by little and thus offers an ongoing protection.
The idea was to extend the conservation time for a chicken breast would go to 15 days from the current seven days. The results were negative.
However, the research indicated that the coating formed a second skin on the breast. Various additives, such as antimicrobians, could be added to this second "skin", he suggests.
Despite the fact that the coatings did not manage to extend shelf life, he showed that the WPI forms a film on chicken breasts that is homogeneous, transparent, has good adhesion and is not easily perceived by the naked eye.
He holds that while WPI films are the packaging of the future, the commercial exploitation of the application has yet to materialize. The main obstacle is the current high startup cost of developing and using such films. As edible coatings are still in the research stage, enterprises do not have the technology needed to apply the system.
For the moment, the use of WPI films is restricted to products with high added-value. For example a research team at the university's food technology section is studying the application of edible films to turrón, a sweet nougat popular in Spain.
The edible film would eliminate the use of aluminium foil currently used to protect the product. The project is still in the study phase.
Despite the advantages presented by the experts, there exists a number of obstacles to the full development of this alternative system. The main one is that of cost. As edible coatings are still in the research stage, enterprises do not have the technology needed to apply the system. For the moment, its current use is restricted to products with high added-value. This is why, amongst the most immediate projects of the research team from the Food Technology Area at the University, is the application of edible films to turrón (sweet nougat), in order to eliminate the aluminium foil currently used to protect it and so that the product would have only one protective coating. This project is still in the study phase.
Fernández completed the project for his PhD thesis.