Using synchrotron FTIR spectroscopy to determine secondary structure changes and distribution in thermoplastic protein

Abstract

Blood meal is a high protein, low value by-product of the meat processing industry that can be converted into a thermoplastic material by extrusion with a combination of a surfactant, urea, a reducing agent, water, and plasticiser. Changes in protein structure after each processing step (mixing with additives, extrusion, injection molding, and conditioning) were explored using synchrotron FTIR microspectroscopy. Blood meal particles were found to have higher β-sheet content around the perimeter with a randomly structured core. α-Helices were either located near the core or were evenly distributed throughout the particle. Structural rearrangement consistent with consolidation into a thermoplastic was seen after extrusion with processing additives, resulting in reduced α-helices and increased β-sheets. Including triethylene glycol as a plasticiser reduced α-helices and β-sheets in all processing steps. At all processing stages, regions with increased β-sheets could be identified suggesting blood meal-based thermoplastics should be considered as a semicrystalline polymer where clusters of crystalline regions are distributed throughout the disordered material.