Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2016
Publication Date: 4/19/2016
Citation: Otoni, C.G., Avena Bustillos, R.D., Olsen, C.W., Bilbao-Sainz, C., McHugh, T.H. 2016. Mechanical and water barrier properties of isolated soy protein composite edible films as affected by carvacrol and cinnamaldehyde micro and nanoemulsions. Food Hydrocolloids Journal. 57:72-79.
Interpretive Summary: The study was motivated by the rising demands for novel bio-based materials to be used in food packaging. We developed isolated soy protein-based edible films incorporated with carvacrol and cinnamaldehyde (the major components of oregano and cinnamon essential oils, respectively) micro or nanoemulsions. Our main objectives were to thoroughly characterize the mechanical and water barrier properties of the films as well as to evaluate the effect of emulsion addition and droplet size reduction on tensile strength, elongation at break, elastic modulus, water vapor permeability, total pore volume, water sorption kinetics, and water diffusivity. Among other interesting results, we showed that water vapor probably migrated through pores present in isolated soy protein films and not through the hydrophilic polymeric matrix itself. This finding is supported by the microvoid model of water permeation.
Technical Abstract: Edible films may be used in food packaging, for which they must deliver good barrier and mechanical properties. Films based on proteins have good gas barrier and mechanical properties, but poor water barrier properties. Films made from lipids have good water barrier properties, but poor mechanical properties. Protein and lipids were then combined to form composite films, and the particle size of the lipid phase was reduced to evaluate its effect on the mechanical and barrier properties. Micro and nanodroplets of Acetem and Tween 60 were added into an isolated soy protein (ISP) solution. Oil-in-water droplets were formed by direct emulsification at 1,300 rpm for 30 min (microdroplets) or 5 h (nanodroplets), dispersed into the ISP solution, and cast into films. Emulsified films showed reduced strength and increased elongation, indicating a plasticizing effect of emulsions. The water barrier properties were either unchanged or slightly improved by the addition of hydrophobic compounds. Reducing droplet size improved the barrier properties as surface area of the lipid increased. Carvacrol and cinnamaldehyde were also added, and they either improved or unaffected the mechanical and barrier properties of ISP films. Addition of emulsions and reduction of droplet size generally decreased total pore volume in the films as well as water vapor permeation, indicating that the microvoid model suitably explains the water barrier properties of ISP films. This work further clarifies possible differences in barrier properties by examining water diffusivity and adsorption/desorption kinetics.