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This was the subject of the PhD thesis by Navarre chemist, Javier Osés
Fernández, at the Public University of Navarre. In the research,
various edible coatings were analysed – all based on proteins
extracted from milk serum (whey protein isolate or WPI), mesquite gum
and starch - with the objective of evaluating their possible food
applications.
The PhD, entitled “Development, characterisation and applications for
foodstuffs of edible coatings based on milk serum proteins, starch and
mesquite gum”.
Mesquite gum, an efficacious and cheap solution
To test the efficacy of the edible coatings compared to synthetic
packaging, Javier Osés prepared a number of samples of milk serum
protein films, of mesquite gum and of starch, and stored them for six
months at different humidity levels.
The first conclusion from the study is that, depending on the type of
plastifier used, the mechanical properties change with the passage of
time. Thus, those films with sorbitol plastifier underwent variation
in their mechanical properties, i.e. their flexibility; while those
containing glycerol did not alter their composition. Once the ideal
plastifier for the coating was determined, it was 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, and its
applications are thus very limited. In order to set this deficiency
off, mesquite gum was incorporated into the milk serum protein. This
is a polysaccharide that grows in dry and semi-arid regions of the
north of Mexico. The result is a compound film that is resistant and
that maintains suitable mechanical properties. 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.
The edible coating of fruit is currently the best-known example of the
application. However, it is a packaging system particularly
efficacious for conserving foodstuffs that are high in polysaturated
fatty acids, susceptible to oxidation, such as nuts, meat and certain
fish such as salmon.
In his PhD, Javier Osés evaluated to what extent the edible films
which he had developed were able to protect fatty foods. To this end,
he used a model foodstuff – sunflower oil. In a first stage, trials
were carried out with WPI coatings. 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. Thus, 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 second stage involved a similar experiment, but with films made of
starch, known to be an efficient barrier to oxygen, and with which
trials were undertaken. In this case, the thickness of the film did
not influence the protector effect on the oil, but it was shown that
starch films are more effective in ambiences with high relative
humidity.
The final part of the PhD outlined the application of edible coatings
with WPI on chicken breasts. The aim was to analyse the effect on
their aspect and their properties. At the same time, the experiment
was used to 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 from the current 7 days to 15, but the results were negative.
However, a very interesting line of research was opened as it has been
shown that the coating formed a second skin on the breast and onto
which various additives, such as antimicrobians, can be added.
Despite the fact that the coatings did not manage to reduce microbian
evolution, it has been shown that the WPI forms a film on chicken
breasts which is homogeneous, transparent, has good adhesion and is
not easily perceived by the naked eye.
The future of packaging
Currently, the three systems of conservation most used by the food
industry are vacuum packing, nitrogen sweeping and aluminium foil. The
Pamplona research chemist holds that WPI films are the packaging of
the future, although the commercial exploitation of the application is
yet to materialize. There are many possibilities – on the one hand,
they will prolong the useful life of foodstuffs in a healthy way and,
on the other, they will be very beneficial for the environment given
that they will reduce the use of plastics.
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.
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