Preparation and characterization of biodegradable polymer films from cowpea (Vigna unguiculata) protein isolate
Journal of the National Science Foundation of Sri Lanka
The investigations on a variety of proteins present in corn zein, wheat gluten, milk whey and soya have shown that these proteins possess the ability to form films which can be used in food packaging. We, therefore, selected cowpea (Vigna unguiculata), a cereal abundantly available in Sri Lanka, to investigate its polymer film forming ability. Our studies have shown that the choice of a suitable solvent, pH of the medium and the use of a plasticizer were essential to obtain useful films. In
... study polyethylene glycol and glycerol were used as plasticizers. The extracted cowpea protein and the plasticizers were dissolved in hot aqueous ethanol to obtain a viscous solution. The casting technique was used to fabricate the films. A series of films were made by varying the pH from 8 to 11. For each pH a series of films was prepared by varying the concentration of polyethylene glycol from 2.5 to 10% (w/v). The fabricated films were tested for transparency, glass transition temperature, tensile strength and water vapour permeability. The pH of the medium and the concentration of the plasticizer were found to have a considerable effect on the physico-chemical properties of the film. The film fabricated at pH 10 with 2.5% (w/v) of polyethylene glycol and 2% glycerol was found to possess the desired tensile strength, water vapour permeability, transparency and glass transition temperature, making the film suitable to be used as an edible food packaging material.