Characterization of agar/soy protein biocomposite films: Effect of agar on the extruded pellets and compression moulded films

• Transparent films were successfully obtained by extrusion and compression moulding.
• Agar caused conformational changes in protein due to agar-protein interactions.
• Film solubility decreased while water uptake increased by the incorporation of agar.

Agar/soy protein biocomposite films were successfully processed by extrusion and compression moulding, obtaining transparent and homogeneous films. The conformational changes occurred during the extrusion process and the effect of agar on the final properties were analyzed. As shown by differential scanning calorimetry (DSC) and specific mechanical energy (SME) values, during the extrusion process protein denatured and unfolded protein chains could interact with agar. These interactions were analyzed by Fourier transform infrared spectroscopy (FTIR) and the secondary structure was determined from the amide I band. Those interactions were supported by the decrease of film solubility. Furthermore, the good compatibility between agar and soy protein was confirmed by the images from scanning electron microscopy (SEM).