Characterisation of eumelanin-chitosan films

Food packaging films based on chitosan (1%, w/v) were developed by optimising chitosan thin films with different concentrations of eumelanin 0, 0.05, 0.1, 0.2 and 0.4% respectively. The properties of eumelanin-chitosan (EU-Ch) films, including colour, water contact angle, mechanical properties, degradation ratio, moisture content (MC), and total soluble matter (TSM), were investigated. The results showed that by increasing eumelanin concentrations, the colour of EU-Ch films changed from transparent to brown. Water contact angles of pure chitosan and EU-Ch films varied 94.55 to 97.49°, demonstrating that chitosan-based films are hydrophobic. The water contact angles remained independent of the addition of eumelanin at all tested concentrations. The EU-Ch films showed better mechanical performance in the wet state. This is an indication that water works as a plasticiser by decreasing stiffness and strength and increasing strain at break. The degradation ratio of pure chitosan films was higher than EU-Ch films with values 25% higher even after 60 days. Moisture content of pure chitosan was higher than EU-Ch films and MC values decreased when eumelanin content was increased. TSM_dry values are lower than TSM_wet values.