Packaging is done to preserve the quality and safety of fruits, vegetables and processed foods in order to increase shelf life. The of most synthetic polymer based packaging are non-biodegradable which can cause increased environmental concern. Nanosilver is used in packaging materials for its antimicrobial effect. A general antibiotic kills only 5-6 sorts of pathogen while silver kills 650 sorts of pathogen and there are no bacteria alive over 6 minutes when they are being contacted with the silver.
Composition of film
Gelatin, chitosan and silver nanoparticles are used in making the biodegradable film. Gelatin which is a heterogeneous mixture of water soluble proteins is used as a component of biodegradable packaging materials. Animal and plant based polysaccharide Chitosan extracted from chitin is used as the second natural biopolymer.
Silver nanoparticles are used in the film to enhance its antimicrobial properties, because nanosilver has been widely used as a coating on various substrates to utilise its sterilizing properties.
Making the film
Researchers of University of Auckland give a procedure to make the film as follows.
Chitosan is dissolved in 2% acetic acid at 20oC. 16% (w/v) Gelatin solution is made with deionised water. The chitosan and gelatin solutions are mixed in relative proportions 1:4 and stirred for 2 h at 50oC with occasional stirring. To this solution, PEG400 together with 3 drops of EDAC is added to give 30% of the substrate mass. Silver nitrate (0.1% w/w) is then added together with sodium borhydride and the solution stirred for 30 min. The solution is then poured into large petri dish and allowed to evaporation at ambient temperature to make the film. In the film silver nanoparticles in the size range 5-10 nm. are found to be distributed.
Packing film is available commercially using colloidal silver which is tasteless does not sting and will not upset the stomach when used as packaging material. This is not a chemical compound containing silver, but pure metallic nanosilver held in suspension, in pure water.