Effect of ultrasound treatment on methylcellulose film properties and application of modified films in packaging of baguette bread

Edible films are generally defined as stand-alone thin layers of materials. They can form pouches, wraps, capsules, bags, or casings in many processes. Coatings are a particular form of films directly applied to the surface of foods. Films are generally prepared using biological polymers such as proteins, polysaccharides and lipids. Edible films have weak mechanical properties and water-vapor permeability (VWP), which can be improved by physicochemical modifications, e.g., ultrasound (US) treatment. Also, edible films, due to their biodegradable nature, can substitute (after appropriate physiochemical modifications) synthetic packaging for foods such as bread. Edible films of methylcellulose (MC) were prepared and the effects of US treatment (5-, 15-, 30- and 45-min durations) on their WVP, tensile strength (TS), and percentage elongation at break (E%) were determined. The effect of relative humidity (52, 57 and 75%) on WVP of the films was also determined. In addition, we also investigated the ability of applied wrappings to retard baguette bread staling by assessing the mechanical and organoleptic properties of breads. 15µm films containing 45% glycerol, treated with ultrasound waves for 5min (the best conditions), were selected and their effect on retarding bread baguette staling determined. Results showed a significant effect of ultrasound treatment on the MC films’ WVP and mechanical properties. Moreover, relative humidity influenced WVP of the films. The MC films retarded staling of the bread samples only for one day. Ultrasound treatment can affect physical and mechanical properties of MC films to a large extent. Mechanical and organoleptic tests of bread indicate that the wrapping can retard staling of baguette bread only for one day. Thus, more research in needed to elucidate more light on the applicability of edible MC films in food packaging.