Isolation and Characterization of an Aggregating Peptide from a Tryptic Hydrolysate of Whey Proteins

Spontaneous precipitation of a peptide mixture has been observed during the concentration by reverse osmosis of a tryptic hydrolysate of whey protein. The precipitated material collected by centrifugation could not be solubilized by urea, mercaptoethanol, or sodium dodecyl sulfate. However, a complete solubilization of the aggregates was observed when the pH of the solution was lowered to 2.0. Analysis of the insoluble fraction has allowed the identification of β-lactoglobulin (β-lg) fragment 1−8 as the major peptide involved in the formation of aggregates. Peptide β-lg f1−8 accounted for >94% of the peptide content in the precipitate washed twice with distilled water. The investigation of the secondary structure using circular dichroism evidenced that the peptide β-lg f1−8 isolated from the flocculated peptide mixture is under random coil conformation at acidic and neutral pH and tends to adopt a β-sheet conformation at basic pH. The findings of this study provide evidence that peptide β-lg f1−8 forms aggregates via an efficient self-assembly process.