Enhanced edible films of mixed biopolymers for controlled release

Licentiatavhandling, 2005

In recent years there has been a growing interest and increased intensity of research in the area of edible films and coatings. Edible films and coatings can improve quality and shelf-life of food products by acting as barriers to e.g. moisture and oxygen, hence preventing dehydration and oxidative reactions. They can also be used as carriers of active components, such as preservatives, which are released to the food product to provide additional protection. Many edible biopolymers form good oxygen barriers, but are often moisture sensitive, which can be reduced by mixing with more hydrophobic components. By combining the good gas barrier of hydrophilic biopolymers with the moisture protection of more hydrophobic components, enhanced, tailor-made films can be produced. Two biopolymers are, however, rarely miscible in solution and the phase separation behaviour is therefore important for the final film structure and its properties. The effect on water vapour permeability and mechanical properties of addition of various amounts of an acetylated monoglyceride (Acetem) to starch films was studied. The effects on phase separation in these films were also evaluated after different drying temperatures. It was shown that the water vapour permeability was decreased by addition of Acetem and higher drying temperatures. Addition of Acetem had greater impact on the mechanical properties than the drying temperature. The phase separation behaviour of a mixture of a modified high amylose starch (hylon) and the maize protein zein was investigated. The phase separation process was studied in real-time in a confocal laser scanning microscope during cooling and during solvent evaporation. During cooling small droplets of hylon appeared and aggregation occurred to some extent. Solvent evaporation had greater impact on phase separation, which in this case took place through two steps. During the first step large hylon network aggregates were formed. During the second step small droplets of hylon appeared and coalesced with other droplets and the aggregates formed earlier. The second step of the phase separation seemed to take place through spinodal decomposition. Microbial attack on the surface of a food product can be prevented by adding active components to an edible film or coating. The active components can be released to the surface of the food product, where it is needed the most. In a study, release of components with different molecular weight from kafirin films into model foods with different water activity was investigated. It was shown that both the water activity and the molecular weight of the release components affected the release.