Development of edible chitosan based packaging film with improved physicochemical and biological properties

Abstract

Chitosan is a promising material for making edible, active and biodegradable packaging films for foods; however, pure chitosan films have poor mechanical and barrier properties. This Master of Philosophy study was conducted with the aim to improve the physicochemical and biological properties of chitosan films by incorporating epoxy activated agarose (EAA) and three flavonoids, namely catechin, quercetin and luteolin into the film. Chitosan films were prepared with chitosan of three molecular weights (low, medium and high) and by drying at 21 °C, 40 °C and 50 °C. EAA and the flavonoids were incorporated into chitosan, both at 1-10%. With increased MW of chitosan, the film thickness, tensile strength (TS), elongation at break (EAB), and swelling ability increased while the moisture content, solubility, water vapor permeability (WVP) and the melting temperature declined. Higher drying temperatures led to greater TS and higher melting temperature for the films. Incorporation of the EAA significantly improved the moisture related properties and flexibility of the chitosan films. Moreover, with higher amounts of EAA, the film thickness and opacity increased while the TS and thermal stability declined. Incorporation of flavonoids had significant (type and concentration dependent) impact on the physicochemical and biological properties of chitosan films. Addition of flavonoids up to 5% resulted in films with greater TS, EAB and thermal stability, whereas at concentrations of up to 3%, the films produced had improved WVP. All the chitosan-flavonoid composite films exhibited antimicrobial activity against Listeria monocytogenes, Salmonella typhimurium, Escherichia coli and Staphylococcus aureus. Beef samples wrapped with pure chitosan or chitosan-flavonoid composite films had significantly lower microbial counts and a more reddish color after two weeks of storage at 4 °C than those packaged with cling wrap. Storage of the chitosan films at 21 °C and 4 °C for six weeks resulted in significant reductions in the TPC, TFC, antioxidant activity and the flexibility of the films, which occurred at a faster rate at 21 °C. Overall, this study demonstrated that incorporation of EAA and flavonoids at appropriate levels can significantly improve some of the physicochemical and biological properties of chitosan films.