Characterisation of composite films fabricated from collagen/chitosan and collagen/soy protein isolate for food packaging applications

This study was undertaken to evaluate the potential of collagen/chitosan (CG/CH) and collagen/soy protein isolate (CG/SPI) composite films for food packaging applications. Two types of composite films at different blend ratios of CG/CH or CG/SPI (100, 8, 2, 6,4, 55 and 010%, w/w) using 30% (w/w) glycerol as plasticiser were prepared and characterised. The results of mechanical tests of the CG/CH composite films displayed higher elongation at break point (EAB), but lower tensile strength (TS) and modulus of elasticity (E), compared to the CG film (P < 0.05). Conversely, the CG/SPI composite films exhibited lower EAB, but greater TS and E values (P < 0.05) compared to the CG film. Water vapour permeability (WVP) increased markedly in the CG/CH composite films; whilst it was found to decrease in CG/SPI composite films at the different blend ratios tested (P < 0.05). Transparency values and water solubility of CG/CH and CG/SPI composite films were decreased substantially, compared to the CG film (P < 0.05). Lower light transmission was observed in all composite films in ultraviolet (UV) and visible regions (200-800 nm), indicating improved UV blocking capacity. Intermolecular interactions through hydrogen bonding among polymeric components were dominant in the CG/SPI (8:2) composite film as elucidated by FTIR analysis. Thermo-gravimetric curves demonstrated that CG/CH (82) and CG/SPI (82) composite films exhibited lower heat susceptibility and weight loss (%), as compared to the CG film in the temperature range of 30-600 °C. DSC thermograms suggested that the compatible blend of CG/SPI (8:2) rendered a solid film matrix, which consisted of highly ordered and aggregated junction zones. SEM micrographs revealed that both CG/CH (8:2) and CG/SPI (8:2) composite films were slightly rougher than the CG film, but no apparent signs of cracking and layering phenomena were observed, thereby highlighting their potential use as biodegradable packaging materials.