Effect of sonication and succinylation on rheological properties and secondary structures of date palm pollen protein concentrate

The rheological properties and the secondary structures of date palm pollen concentrates were investigated in the present study. The sonication pretreatment and the succinylation procedure were applied to the native protein, as physical and chemical modifications, respectively. Each modification affected differently the native concentrate. In fact, in the flow measurement, results, fitted with the power low model, showed that sonication increased the consistency coefficient and decreased the flow index implying a more shear-thinning character. However, for succinylation modification, an increase of the flow index and a decrease of the consistency coefficient were noticed which convert the protein concentrate to a less viscous and more Newtonian-like state. Sonication also enhanced the thixotropic behavior which was expressed by the increase of the hysteresis loop, whereas the succinylation suppressed it, which was deduced from the disappearance of the loop area. The frequency sweep analysis proved that the sonicated concentrate was characterized by a strong gel structure while the succinylated protein had a viscoelastic liquid character. Only the native and the succinylated concentrates gelified, in the temperature sweep test, at 53.1 and 54.4 °C, respectively. All discerned differences were attributed to the secondary structure content. The findings revealed that the sonicated protein had a high β sheet content, leading to greater thermal stability which proved that a higher temperature is required to ensure the gelation of the protein. However, native and succinylated concentrates were found to have an equilibrium between α helix and β sheet which made it possible to form a stable gel at a lower temperature. The present study concluded that the modifications had a great impact on the rheological properties which was strongly attributed to the submitted structural changes.