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Effect of Physicochemical Conditions on Peptide−Peptide Interactions in a Tryptic Hydrolysate of β-Lactoglobulin and Identification of Aggregating Peptides

Groleau, Paule Emilie, Morin, Pierre, Gauthier, Sylvie F., Pouliot, Yves
Journal of agricultural and food chemistry 2003 v.51 no.15 pp. 4370-4375
acidification, beta-lactoglobulin, disulfide bonds, electric field, emulsifying properties, hydrolysates, hydrophobic bonding, ionic strength, isoelectric focusing, lactalbumin, pH, peptides, reducing agents, salt concentration, sodium chloride, solubility, temperature, turbidity, urea
The objective of this study was to characterize the changes in peptide solubility resulting from changing some physicochemical conditions in a tryptic hydrolysate of β-lactoglobulin (β-LG). The turbidity (500 nm) of a 1% solution of tryptic peptides was measured at pH 3−10, at 5, 25, and 50 °C, in the presence of different salt concentrations (0, 0.5, and 1 M NaCl), in the presence of denaturing and reducing agents (6 M urea, 5% SDS, or 5% β-mercaptoethanol), and under an electric field (isoelectric focusing). The results reveal an increase in turbidity of the peptide solution at pH 4, but a slight increase in turbidity was also observed at pH 8, which is attributable to peptides linked by disulfide bridges. The effect of temperature and ionic strength on the turbidity occurring at pH 4 indicates that mainly hydrophobic interactions are involved in the aggregation process. The material in the precipitate at pH 4 was identified as the peptides β-LG 1−8, 15−20, and 41−60 and non-hydrolyzed α-lactalbumin. These results suggest that a limited number of peptides are involved in the aggregation process observed at pH 4, some of which having bioactive (β-LG 15−20, ACE inhibitor, and opioid) or emulsifying properties (β-LG 41−60). Aggregation of these peptides at acidic pH indicates that a simple acidification step could represent an easy process for isolating peptidic fractions enriched in bioactive or functional peptides.