Enhancement and Characterization of Films for Barrier and Release Applications

Doctoral thesis, 2007

Films and coatings can improve the quality and shelf-life of food products by acting as barriers to e.g. water vapour and oxygen. Many edible biopolymer films, based on polysaccharides and proteins, form excellent oxygen barriers but most often provide only poor water vapour barriers. Lipids on the other hand are hydrophobic and can provide better water vapour barrier properties. Films with enhanced and tailored properties can be produced by combining the good gas barrier properties of hydrophilic biopolymers with the moisture resistance of more hydrophobic components. This work focused mainly on the water vapour barrier and release properties of films and coatings to gain a deeper understanding of how material properties can affect such properties. The effect on water vapour permeability and mechanical properties of starch films was evaluated after addition of an acetoglyceride and the effect on phase separation was determined after film formation at different temperatures. The water vapour permeability of starch films was decreased by addition of the acetoglyceride and by using higher drying temperature. Addition of the acetoglyceride had a weakening effect on the films, whereas the drying temperature showed no great effect on the mechanical properties. Mixed film-forming systems most often phase separate during film formation. The phase separation behaviour of a mixture of an acetylated high amylose maize starch and the maize protein zein was studied in real-time during cooling and during solvent evaporation. It was concluded that solvent evaporation had a greater impact than cooling on the phase separation, but both the solution temperature during cooling and the solution composition during solvent evaporation affected the phase separation. The concentrations of the two biopolymers in the solution had impact on the formed microstructures. Active components can be incorporated in biopolymer or lipid films and be used in release applications. The release of two preservatives and four sugars from films made from the protein kafirin into model foods with different water activity was evaluated. It was concluded that the water activity of the model food had a great impact on the release from the film and diffusion of released substances in the model food. Two hydrophobic petroleum waxes, a petrolatum and a microcrystalline wax, with different water vapour barrier properties were investigated to gain a deeper understanding of inherent material properties that can affect the barrier properties. The petrolatum showed a more open crystalline structure, while a more network-like crystalline structure was seen in the microcrystalline wax. Both waxes melted and crystallized over a broad temperature range. The microcrystalline wax crystallized through a two-step process and the petrolatum crystallized through a one-step process. Recrystallization occurred in both waxes during ageing.