Investigation of the Protein-Protein Aggregation of Egg White Proteins under Pulsed Electric Fields

Egg whites were exposed to pulsed electric fields (PEFs) to investigate the protein-protein aggregation. No insoluble protein aggregate was found when egg whites were exposed to PEFs at 25, 30, and 35 kV/cm for 400 mu s. However, atomic force microscopy showed that the sizes of the protein particles increased. Native polyacrylamide gel electrophoresis (PAGE) demonstrated the existence of aggregates under PEFs at 35 kV/cm for 400 mu s. Sodium dodecyl sulfate (SDS)-PAGE in the presence and absence of 2-mercaptoethanol further indicated that sulfhydryl-disulfide interchange reactions occurred under PEFs. Differential scanning calorimetry scans showed 400 mu s of PEF treatment at 35 kV/cm denatured 16.5% proteins. Insoluble egg white protein aggregates were induced by PEF (35 kV/cm, 800 mu s) and heat (60 degrees C, 3.5 min) treatments. Disulfide bonds were the dominant binding forces in the formation of protein aggregates. However, the weakly noncovalent bonds play a much more important role in the protein aggregation forming in heat treatment (60 degrees C, 3.5 min) than that in PEF treatment (35 kV/cm, 800 mu s).