Thermo-mechanical properties of egg albumen–cassava starch composite films containing sunflower-oil droplets as influenced by moisture content

The effect of moisture content on the thermo-mechanical and structural properties of egg albumen–cassava starch composite films containing sunflower oil droplets was studied using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Composite films were prepared by cold gelation, dried in a moisture controlled incubator (83.5%RH) at 25 °C for 8 days and aged at different relative humidity at room temperature (21 ± 1 °C) for 7 days to obtain composite films with moisture contents of 4%, 7%, 11%, 17% and 46% (dry weight basis). In DMA thermograms the magnitude of G′ and G″ increased with increasing temperature in high-moisture samples, decreased and then again gradually increased for intermediate-moisture samples, and decreased in low moisture samples. DSC thermograms indicated two distinct peaks (at 49–53 °C and 79.8 to 132.4 °C) which were attributed to phase transitions and protein denaturation. SEM images indicated that the microstructure of the composite matrix changed with moisture content and heating temperature. Our study confirms that moisture content plays a key role in the thermo-mechanical properties and microstructure of egg albumen–cassava starch composite films containing sunflower oil.