Multifunctional barrier films and coatings from biopolymers via enzymatic modification

Widely used synthetic polymers (e.g. HDPE) in food packaging possess excellent barrier properties against moisture and water vapour, but they have high permeability for oxygen and grease. Unlike plastics, films casted of carbohydrates or proteins are good barriers against oxygen and grease. However, polysaccharides and most proteins are hydrophilic in nature and films produced from these materials are often hygroscopic, resulting in substantial loss of their barrier properties at high humidity. Commonly suggested methods to decrease moisture sensitivity of bio-based polymers are chemical grafting with hydrophobic components, such as natural waxes or fatty acids, or compounding with synthetic polymer. Novel enzymatic technology was developed to decrease hydrophilicity of natural biopolymers. Enzymatic cross-linking and subsequent functionalisation of hemicellulose and protein with hydrophobic alkyl gallates (e.g. dodecyl gallate) resulted in improved barrier properties at humid conditions. The method involved utilisation of oxidative enzymes, tyrosinase and laccases, to solidify the matrix material into an insoluble network structure with concomitant modification with hydrophobic functional groups. Barrier properties could be further improved by controlled addition of inert nanomaterial, such as nanoclay.