Characteristics and Effects of Specific Peptides on Heat-Induced Aggregation of β-Lactoglobulin

A bovine beta-lactoglobulin hydrolysate, obtained by the hydrolysis by the Glu specific enzyme Bacillus licheniformis protease (BLP), was fractionated at pH 7.0 into a soluble and an insoluble fraction and characterized by LC-MS. From the 26 peptides identified in the soluble fraction, five peptides (A[f97-112] = [f115-128], AB [f1-45], AB[f135-157], AB[f135-158], and AB [f138-162]) bound to beta-lactoglobulin at room temperature. After heating of beta-lactoglobulin in the presence of peptides, eight peptides were identified in the pellet formed, three of them belonging to the previously mentioned peptides. Principle component analysis revealed that the binding at room temperature (to beta-lactoglobulin) was related to the total hydrophobicity and the total charge of the peptides. The binding to the unfolded protein could not be attributed to distinct properties of the peptides. The presence of the peptides caused a 50% decrease in denaturation enthalpy (from 148 +/- 3 kJ/mol for the protein alone to 74 +/- 2 kJ/mol in the presence of peptides), while no change in secondary structure or denaturation temperature was observed. At temperatures < 85 degrees C, the addition of peptides resulted in a 30-40% increase of precipitated beta-lactoglobulin. At pH < 6, no differences in the amount of aggregated beta-lactoglobulin were observed, which indicates the lack of binding of peptides to beta-lactoglobulin at those pH values as was also observed by SELDI-TOF-MS. Although only a few peptides were found to participate in aggregation, suggesting specificity, principal component analysis was unable to identify specific properties responsible for this.