Aggregate Formation during Hydrolysis of β-Lactoglobulin with a Glu and Asp Specific Protease from Bacillus licheniformis

Abstract

The hydrolysis of isolated β-lactoglobulin (9 and 70−200 mg/mL) by a Bacillus licheniformis protease was followed to assess whether aggregates and gels, respectively, were formed during hydrolysis. Changes during hydrolysis were monitored by electrophoresis, dynamic light scattering, and fluorescence and circular dichroism spectroscopy. Gelation was monitored by dynamic oscillation rheology. Upon hydrolysis of a β-lactoglobulin preparation with the B. licheniformis protease aggregates were formed and a soft gel resulted from only 70 mg/mL of β-lactoglobulin. The aggregates consisted of a number of peptides with molecular weight ranging from 2000 to 6000 and pI from 5 to 8. As the aggregates were solubilized in either SDS or urea or at extreme pH values, it is proposed that noncovalent interactions, mainly electrostatic and hydrophobic, are major interacting forces. These kinds of aggregates are thought to be important in protease-induced gelation of whey protein isolate solutions. Keywords: β-Lactoglobulin; proteolysis; aggregation; fluorescence; circular dichroism