In the aim to reduce the total amount of preservatives added in food, edible coating is used in the present
study as surface retention of active agents to maintain a local high effective preservative concentration where
microorganisms are intended to contaminate and/or grow, i.e. on coating surface. A food/anti-microbial
coating system with sorbic acid as the active compound, agar gel as model food and wheat gluten (WG) or
beeswax (BW) film as edible coatings was studied. A mathematical model able to describe the release
kinetics of the anti-microbial agents from the edible coating into food products was developed and validated.
It was used for estimating the local surface concentration in sorbic acid of coated model food. This surface
concentration is an essential value for predicting microorganism growth but cannot be evaluated by
experiments. In the case of WG coating, the surface concentration drops below 10% of the initial value after
1 h whereas in the case of the BWcoating, the surface concentration remains above 75% even after one week
of contact. Simulation realized using the estimated surface concentration and a simplified equation for the
growth inhibition kinetics of Saccharomyces cerevisiae were compared to microbiological efficacy assessment.
The calculated amount of sorbic acid required to maintain a 0.2% surface concentration during 23 days was
100 times lower when introducing the additive in a beeswax thin layer than directly in the core of the high
moisture food or in a hydrophilic film such as wheat gluten.
Industrial relevance: The methodology presented in this study based on experimental measurements and
mathematical predictions is of great interest for the rational design of anti-microbial coatings and could be
used in industrial applications. Edible coatings are already used in commercial practice for their barrier
properties (water barrier property for example to avoid remoistening or drying of cereal-based products, gas
barrier properties for the coating of fresh fruits and vegetable, etc) or for food appearance improvement
(brilliance of apples for examples could be improved using polysaccharide-based film). Edible coatings have
proved to be suitable as vector of preservatives such as anti-microbial or anti-oxidants. By using such retention
matrices, very small amount of additives is required since the preservative is concentrated at the product
surface. The benefit of using anti-microbial edible coating for consumer health is consequently non-negligible
and this aspect is more and more taken into account by food manufacturers. The use of active edible coatings at
an industrial scale is expected to grow, in Europe, due to the European framework regulation (EC 2004/1935)
which authorizes the concept of active packaging with intentional active agents' release.
The efficacy of anti-microbial edible coating could be assessed through time-consuming experimental tests. But
most of the time, the couple ediblematrix/active compound suitable for one applicablewon't be anymore suitable
for another food product and empirical tests should be undertaken once more by the foodmanufacturer. By using
an integrated approach such as the one presented in this work, based on mathematical model for predicting
additive release kinetics, numerous experimentsmay be avoided, since once the preservative diffusivity values in
the coating and the food are known, the numerical tool could be used to optimize the initial quantity of
preservative to add in the coating, to predict the food shelf life as a function of coating thickness or coating
concentration in preservative, etc. The data shown in this paper concerning wheat gluten- and beeswax-based
films could be also added in data bases of industrial relevance for further commercial applications.
The approach used in this study could be considered as an assistant and prediction tool that should (i) optimize
food preservation and (ii) help manufacturers in elaboration of new food product and packaging.