Formation of whey protein isolate nanofibrils by endoproteinase GluC and their emulsifying properties

Nanofibrils have favorable functional properties that facilitate their applications in the food industry. Whey protein isolate (WPI) is widely used to prepare nanofibrils via acid hydrolysis. In this research, the effect of hydrolysis by endoproteinase GluC (GluC) on WPI nanofibrils (WPNFs) was evaluated based on their structural and emulsifying properties. Following the hydrolysis of WPI by GluC at 37 degrees C and pH 8.0, the peptides self-assembled into WPNFs at 37 degrees C and pH 2.0. WPNFs with several micrometric length and nanometric (1-10 nm) diameter exhibited high aspect ratio (length/diameter). Based on microscopic images, circular dichroism spectroscopy, and infrared spectroscopy, we concluded that beta-sheets played an important role in the formation and stability of WPNFs. The main factor affecting WPNF formation was found to be hydrolysis by GluC for 10 h followed by aggregation at pH 2.0. Whey protein hydrolysates with glutamic acid or aspartic acid residues, obtained from WPI hydrolysis by GluC for 10 h, might be positively charged in an acidic environment, thereby favoring the formation of ordered aggregates instead of random ones. WPNFs prepared under such conditions have a strong ability of improving the oxidative stability, activity and stability of emulsions. This new strategy for producing WPNFs will potentially expand their application in the food industry.