Abstract
Whey protein coatings and cast films are promising for use as food packaging materials. Ongoing research is endeavoring to reduce their permeability. The intention of this study was to evaluate the effect of the reactive additives sodium sulfite, sodium dodecyl sulfate (SDS), and urea on the oxygen barrier, water vapor barrier, and protein solubility of whey protein cast films. The concentration of the reactive additives was 1 to 20 wt.-%. Dried whey protein cast films were used as substrate materials. The water vapor transmission rate, the oxygen permeability, and the protein solubility were measured. Effective diffusion coefficients and effective sorption coefficients were calculated from the results of the water vapor sorption experiments. The presence of sodium sulfite resulted in an increased number of hydrophobic interactions and hydrogen bonds and a slightly decreased number of disulfide bonds. The oxygen permeability decreased from 68 to 46 cm3 (STP/standard temperature and pressure) 100 μm (m2 d bar)−1 for 1 wt.-% SDS in the whey protein cast film. The water vapor transmission rate decreased from 165 to 44 g 100 μm (m2 d)−1 measured at 50 to 0% r. h. for 20 wt.-% SDS in the whey protein cast film. The reduction in the water vapor transmission rate correlated with the lower effective diffusion coefficient.
Highlights
Barrier packaging systems for foods and pharmaceuticals have to provide an oxygen barrier as well as a water vapor barrier in order to ensure adequate protection for the packed goods (Buchner, 1999)
Films with urea showed no change in the intermolecular interactions but the oxygen permeability and water vapor transmission rate increased
A more suitable mathematic description is needed to more accurately explain the diffusion behavior in the polymer
Summary
Barrier packaging systems for foods and pharmaceuticals have to provide an oxygen barrier as well as a water vapor barrier in order to ensure adequate protection for the packed goods (Buchner, 1999). For this reason, multilayer plastic films containing one or more barrier layers are usually employed. A commonly used oxygen barrier material is the rather expensive ethylene vinyl alcohol copolymer (EVOH) (Lange and Wyser, 2003; Kucukpinar and Doruker, 2004; Müller, 2013) This petrochemical-based copolymer is neither renewable nor biodegradable (Schmid et al, 2012). An alternative is to use proteins, which have interesting properties that make them promising as a potential renewable substitute for EVOH in multilayer packaging (Cuq et al, 1998; Coltelli et al, 2016; Zink et al, 2016). Bugnicourt et al (2013) and Schmid et al (2012) showed that whey protein coatings and layers are of commercial relevance due to the fact that whey protein formulations have
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