Fibre formation in calcium caseinate influenced by solvent isotope effect and drying method – A neutron spectroscopy study

Abstract

We present an investigation of the dynamics of calcium caseinate as a function of hydration, solvent isotope (H₂O and D₂O) and drying methods (roller drying and spray drying), using quasi-elastic neutron scattering (QENS). These factors are key to the formation of fibres in this material which makes it a potential candidate as a next-generation meat analogue. Using a phenomenological model, we find that the relaxation times of the dry spray dried powder decrease with increasing temperatures, while they do not change for the roller dried powder. The spectra of the hydrated samples reveal two independent picosecond processes, both reflecting localized re-orientational motions. We hypothesize that the faster motion is due to the external protein groups that are hydrophilic and the slower motion is due to the internal groups that are hydrophobic. The solvent effect of D₂O is not limited to the external groups but prevails to the internal groups where less protons are mobile compared to the H₂O hydrated samples. Higher temperatures narrow the number difference in mobile protons, possibly by altering the weak interactions inside the protein aggregates. These findings suggest that a harsh and longer drying process contributes to less active protein side-groups and highlight the hydrophobic effect of D₂O on the fibre formation in calcium caseinate.