Effects of heating or ultrasound treatment on the enzymolysis and the structure characterization of hempseed protein isolates

The effects of heating (90 degrees C/30min) or ultrasound (200/400/600W) treatment on antioxidant and angiotensin-converting enzyme inhibitory (ACEI) activity of hydrolysates from hempseed protein isolates (HPI) were studied. The secondary structure, surface hydrophobicity, intrinsic fluorescence, scanning electron microscopy (SEM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of HPI treated by heating or ultrasound were measured. The results showed that hydrolysate from HPI treated with ultrasound at 200W showed higher hydrolysis degree, proportion of lower molecular mass components (1.0-3.0kDa), antioxidant and ACEI activity than those from heating or high-power treated. The changes in secondary structure, surface hydrophobicity and intrinsic fluorescence indicated the unfolding of HPI after ultrasound. The SEM results showed that HPI treated with ultrasound at 200W exhibited decrease in particle size and deformation and further increased in power caused the aggregates of HPI. In conclusion, the ultrasound treatment at low-power was superior to 90 degrees C/30min treatment in facilitating enzymatic release of antioxidant and ACEI peptides from HPI.