Thermomechanical process induces unfolding and fibrillation of bovine serum albumin

Abstract

Simultaneously thermal and mechanical stresses are experienced by the proteins in most of the practical applications like fluid flow, bioprocessing, formulations, mixing and transportations. In this study, the energetics of thermomechanical treatment of bovine serum albumin (BSA) and its related impact on the unfolding and aggregation behaviour have been explored to decipher the roles of the thermal and dissipation energy. Temperature hysteresis scans of BSA solution at physiological pH (7.4) were conducted in the three temperature ranges i.e. 25-50-25 °C, 25-65-25 °C and 25-75-25 °C to understand its thermal stability. Shear induced aggregation of the BSA at a constant shear rate of 300 s−1 was performed at the three temperatures (55, 60 and 65 °C) and the aggregation behavior was experimentally analyzed. The irreversible unfolding of BSA was observed over its melting temperature. Heat transfer above 3 kJ/mol broke the intramolecular bonds, which resulted in the unfolding and intermolecular interactions (aggregation). Further, the rates of aggregation were enhanced by 1.5 folds for the thermomechanical (sheared) process as compared to thermal treatment. In fact, thermomechanical treatment at even lower 60 °C has a similar impact as thermal treatment at a higher temperature of 75 °C. BSA solution exhibited a shear thickening behaviour during the aggregation. Dissipation energy generated from the shearing was found to accelerate the second step (fibrillation) of the aggregation process at 60 and 65 °C. However, it could not initiate the first step (unfolding) of the aggregation at 55 °C due to the heat loss to the surrounding.