Structural and rheological properties of cereal proteins zein and hordein as a function of temperature and pH

To enhance the sustainability of industrial plant-based meat manufacturing processes, most of which currently involve extensive denaturation of proteins at high temperatures, cereal prolamins, particularly from corn and barley, were investigated for their ability to form viscoelastic gels at low temperatures of < 100 °C, at a variety of pH values ranging between 4.5 to 6.5. These gels had the potential of being stretched into functional fibrous structures, that form the key components of meat alternatives. Since the preliminary analysis of the protein secondary structure through FTIR indicated spectral changes at temperatures as low as 40 °C, viscoelastic gels were formed at a range of processing temperatures varying between 40 to 80 °C, and the rheological and textural properties of the structures so formed were studied. The results indicated that until a temperature of ~77 °C, viscous behavior was more predominant in zein (G” > >G’), beyond which it started to solidify. Hordein, on the other hand, behaved like a viscoelastic material (G’≈G”) until ~68 °C, beyond which it transformed into a more solid-like gel (G’ > >G”). While the hardness of zein and hordein gels increased with an increase in the processing temperature, zein gels, in general, were much more rigid and brittle compared to hordein gels at any given temperature. Further, the strength of the gels was also found to be pH-dependent, with stronger gels being formed at higher acidity. Looking at the intrinsic behavior of two proteins, hordein was blended with zein at specific concentrations to plasticize zein.  Overall, this research gives valuable insights into how hydrophobic plant proteins behave at different temperatures and pH values, which can help improve meat alternative formulations.