Dispersion Coating for Active Food Packaging: Aroma Interactions and Oxygen Scavenging
Abstract: ABSTRACTActive packaging materials prolong the shelf life or preserve the quality of packed food by absorbing oxygen, ethylene, moisture or odours, or by releasing antimicrobial agents, antioxidants or flavours. In dispersion coating, a latex is applied onto paper or paperboard to form a barrier film against water, water vapour, oil or gases. Latex particles have a large specific area and, during drying, an extensive three-dimensional network within the coating layer is created. These surfaces and interfaces were used to create new active packaging materials in terms of odour removal, aroma emission and oxygen scavenging. Styrene-butadiene and styrene-acrylate latices with different degrees of carboxylation were investigated, in the presence and absence of talc or clay fillers.In an odour-removal coating, the partition of the aroma compounds must be towards the film in preference to the gas or liquid phase. The styrene-acrylate films showed a higher affinity for the polar aroma compounds, and the styrene-butadiene films showed a higher affinity for the non-polar aroma compounds, in accordance with the calculated solubility parameters. Addition of talc decreased the affinity of the film for the aroma compounds. To create an aroma-releasing film, aroma solutions were added to the dispersion phase followed by coating and drying, but most of the aroma compounds were lost during the drying process. Talc increased the uptake and retention of the aroma compounds to a large extent. In the films, the diffusivity of the aroma compounds decreased with increased carboxylation of the styrene-acrylate latex particles. It was easier to alter the diffusion and the release rate of the aroma compounds by changing the temperature above and below the glass transition temperature of the polymer film than by varying the amount of carboxylic acids to change the cohesive energy density of the polymer film.The total oxygen-removal capacity of films with enzyme immobilized on latex particles in the dispersion followed by film formation or with entrapped enzyme was higher than that of films with enzyme immobilized on an already formed film, even though a larger amount of enzyme was needed in the former cases. The activity of covalently bonded enzyme was lower than that of entrapped enzyme. With large amounts of clay, the enzyme activity increased. The most suitable storage temperature to retain the enzyme activity was +8ºC, which is close to the Tg of the polymer film.
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