Nanostructure and functionality of enzymatically repolymerized whey protein hydrolysate.

Whey proteins (WPI) were polymerized with transglutaminase (TGase) before and after partially hydrolyzing the protein with thermolysin to produce protein nanoparticles/polymers. Electrophoresis and atomic force microscopy (AFM) were used to determine the size and structural characteristics of the polymers. The foaming and emulsifying properties of these nanoparticles were studied. The polymerized WPI (WPI-TG) produced more stable foams than the repolymerized WPI hydrolysate (WPIH-TG). In contrast, WPIH-TG produced better emulsions with better storage stability than WPI-TG emulsions. These differences were due to their structure and electrostatic properties: The WPI-TG particles were linear, less than 100 nm in size with lower net negative charge, whereas the WPIH-TG polymers were much larger and were highly negatively charged as judged from zeta potential. This suggested that while protein nanoparticles may provide Pickering stability to both emulsions and foams, strong lateral electrostatic repulsion between nanoparticles within the adsorbed film destabilizes foams but not emulsions.