Pressurization-induced molten globule-like protein as a regulatory target for off-flavor controlling: Thermodynamic evidence and molecular modeling

Abstract

To meet the growing demand for protein in underdeveloped countries, the extraction of protein from inexpensive manufacturing by-products plays a crucial role in unlocking the potential of underutilized proteins for food purpose. However, animal-derived protein isolate products often exhibit noticeable off-flavors, significantly hindering the processability of the extracted proteins due to coextraction of off-flavor components that interact with proteins. This work examined the effects of UHP pretreatment (350 MPa/10 min/28 °C) on the interaction between trans,trans-2,4-heptadienal, a representative of off-flavor compounds, and duck liver protein (DLp). The results of multi-spectroscopic characterization suggested the presence of pressure-induced molten globule state (MGs)-like proteins, explaining the increased binding constant values following pressurization. Static quenching was demonstrated during the interaction process between trans,trans-2,4-heptadienal and DLp, without forming novel secondary binding sites. Thermodynamic analysis showed that the spontaneous binding process was mainly driven by hydrogen bonds and van der Waals forces, as corroborated by molecular modeling methodologies, demonstrating the roles of UHP-mediated conformational compression in affecting the flavor-protein complex formation. The interaction of trans,trans-2,4-heptadienal with DLp altered the protein thermostability, which was compromised by UHP pretreatment. The denaturation enthalpy of DLp samples decreased from 1879 J/g to 1225 J/g after UHP, validating the reduced thermostability by UHP and the varied interaction processes of trans,trans-2,4-heptadienal with folded and MGs-like DLp. This investigation demonstrated the tunable interaction processes of off-flavor components with matrix proteins by introducing suitable physical disturbance prior to extraction.