Proteolysis kinetics and structural characterization of ultrasonic pretreated sunflower protein

Proteolysis kinetics and structure attributes of sunflower meal protein (SMP) pretreated using sonication of frequency type single (20, 40 kHz) and dual (20/40 kHz) were examined. A simplified model with impeded enzyme reaction was developed and the proteolysis of SMP in a heterogeneous system was successfully described. Initial observed rate (k(in)) increased after sonication, demonstrating the impacts of sonication on SMP by enhancing proteolysis (enzymolysis) and altering the structure of SMP, which was validated by circular dichroism (CD) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and sodium dodecyl sulfide polyacrylamide gel electrophoresis (SDS-PAGE) analyses. From SMP characterization, there was a reduction in alpha-helix, enhancement in absorption intensity and alterations in functional groups of SMP following sonication. SEM and AFM observations indicated that sonicated SMP unfolded and exhibited more heterogenous structures, and irregular small-sized particles than control, especially at 20/40 kHz. SDS-PAGE profile displayed notable changes in molecular weight after sonication, which evidenced limited unfolding in SMP conformation. The kinetic model has possibility of being used to control enzymolysis; and structural attributes could guide in the development of ultrasonic equipment for use of pretreating protein for enzymolysis.