Plant extracts as additives in biodegradable films and coatings in active food packaging

Petroleum-based polymers are widely used and known that they cause serious environmental problems due to their non-biodegradability. To this end, researchers have focused on the development of ecological packaging materials from natural resources, such as polysaccharides and proteins. However, the films and coatings produced from natural biopolymers have fewer desirable properties than synthetic polymers. Studies have showed that plant extracts represent an interesting ingredient for biodegradable food packaging by altering the properties of biopolymers. The scope of this review is to present the latest ideas on active packaging and how plant extracts impact properties like physical, mechanical, barrier, structural, antioxidant, antimicrobial and the biodegradability of the films. Most of the plant extracts increased the thickness of the biopolymer, reduce the transparency and water vapour permeability, and have adverse effects on the mechanical properties (tensile strength and elongation at break), and alters the biodegradation rate of the films and coatings. The microstructural of the films changed when the plant extracts are added into the solution and the colour of the films depended on the variety of polyphenols that each plant extract contained. Additionally, in most cases natural extracts can boost the antioxidant and antimicrobial properties, thus improve the shelf life of packaged food. Besides the promising results obtained from the literature, there is a lot to achieve, in relation to product quality, shelf life and consumer acceptance of extract-based films on food products.