Influence of thermal process on structure and functional properties of emulsion-based edible films

Synthetic food packaging is classically used to prevent mass transfer of various small molecules (water, gases, flavour compounds or solutes) between a food and its surrounding medium. In the case of composite foods, the development of edible films and coatings, applied between the different phases of this food is rising up. The increase of such food products shelf-life is indeed related to the barrier efficiency of these edible packaging against small molecules transfers. This is especially true for water transfer between compartments of different water activities in the same food, that leads to important physico-chemical changes and therefore to food quality deterioration. Film-forming substances used for this study associated an iota-carrageenan hydrocolloid matrix, that ensures good mechanical properties, in which a high melting point fat was dispersed to enhance moisture barrier properties. After the film drying in standardised conditions of temperature (30 °C) and relative humidity (40%), the emulsified films containing various contents of fat (30%, 60% or 90% dry basis) were also submitted to heat treatment (100, 150, 200 °C) and for different durations (1, 2, 4, 8 min) corresponding to those classically encountered in baking processes. The aim was to tend to a bilayer film structure from a single film manufacturing. Size and repartition of fat globules in the carrageenan matrix was characterised by laser light granulometry and film microstructure was observed by ESEM. Barrier efficiency to water was evaluated from water vapour permeability measurements. Contrary to previous observations on film drying, neither fat globule size nor film water permeability was significantly modified by such heat treatment. Moreover, no phase separation was noticed by microscopic observations of the film cross section. Therefore, carrageenan matrix represents a very powerful material for its structural properties to a system and is a good candidate for application such as encapsulation of active substances incorporated in biopolymer coatings or films for food packaging applications.