Abstract
Whey protein isolate (WPI)-based cast films are very brittle, due to several chain interactions caused by a large amount of different functional groups. In order to overcome film brittleness, plasticizers, like glycerol, are commonly used. As a result of adding plasticizers, the free volume between the polymer chains increases, leading to higher permeability values. The objective of this study was to investigate the effect of partially substituting glycerol by hydrolysed whey protein isolate (h-WPI) in WPI-based cast films on their mechanical, optical and barrier properties. As recently published by the author, it is proven that increasing the h-WPI content in WPI-based films at constant glycerol concentrations significantly increases film flexibility, while maintaining the barrier properties. The present study considered these facts in order to increase the barrier performance, while maintaining film flexibility. Therefore glycerol was partially replaced by h-WPI in WPI-based cast films. The results clearly indicate that partially replacing glycerol by h-WPI reduces the oxygen permeability and the water vapor transmission rate, while the mechanical properties did not change significantly. Thus, film flexibility was maintained, even though the plasticizer concentration was decreased.
Highlights
Protection against negative impact from the environment is the primary function of food packaging [1]
The equilibrium moisture content (EMC) was measured at films conditioned at 23 °C and 50% r.h
The results indicate a minor trend towards reduced EMCs when molecular weight (MW) and Gly content are decreased (Figure 1)
Summary
Protection against negative impact from the environment is the primary function of food packaging [1]. The required oxygen barrier properties in order to maintain the low oxygen concentration in the headspace of MAP packages are often provided by petroleum-based materials, like PA (polyamide), or engineered oxygen barrier polymers, such as ethylene-vinyl-alcohol (EVOH) or polyvinyl alcohol (PVOH), in multilayer structures [3]. These passive barrier functions can be combined with active barrier layers in order to support the passive barrier and to reduce harmful oxygen in the headspace of a package [4]
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