Abstract
Protein based films are nowadays also prepared with the aim of replacing expensive, crude oil-based polymers as environmentally friendly and renewable alternatives. The protein structure determines the ability of protein chains to form intra- and intermolecular bonds, whereas the degree of cross-linking depends on the amino acid composition and molecular weight of the protein, besides the conditions used in film preparation and processing. The functionality varies significantly depending on the type of protein and affects the resulting film quality and properties. This paper reviews the methods used in examination of molecular interactions in protein films and discusses how these intermolecular interactions can be quantified. The qualitative determination methods can be distinguished by structural analysis of solutions (electrophoretic analysis, size exclusion chromatography) and analysis of solid films (spectroscopy techniques, X-ray scattering methods). To quantify molecular interactions involved, two methods were found to be the most suitable: protein film swelling and solubility. The importance of non-covalent and covalent interactions in protein films can be investigated using different solvents. The research was focused on whey protein, whereas soy protein and wheat gluten were included as further examples of proteins.
Highlights
The amino acid sequence of the protein is crucial for possible intermolecular cross-linking
This work gives an overview of methods to determine and quantify intermolecular cross-links
SDS-PAGE and size exclusion chromatography identify intermolecular cross-linking by increase of the molecular weight by aggregation
Summary
Most importantly it maintains the quality and safety of packed foods. The quality of the food has to be ensured during the whole life cycle, this includes transportation and storage at the retailors and customers. To provide safe foodstuffs it is necessary to protect them depending on their respective requirements against oxygen, water vapor, contamination, and physical, chemical, or biological damage [1]. To achieve these requirements multilayer films are widely used in the food packaging sector [1]. One example is ethylene vinyl alcohol (EVOH), which is embedded in other polyolefins and/or polyesters, providing a high oxygen barrier. EVOH is neither renewable nor biodegradable [2,3]
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