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

Abstract

The objective of this study was to characterize the changes in peptide solubility resulting from changing some physicochemical conditions in a tryptic hydrolysate of beta-lactoglobulin (beta-LG). The turbidity (500 nm) of a 1% solution of tryptic peptides was measured at pH 3-10, at 5, 25, and 50 degrees 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% beta-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 beta-LG 1-8, 15-20, and 41-60 and non-hydrolyzed alpha-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 (beta-LG 15-20, ACE inhibitor, and opioid) or emulsifying properties (beta-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.

Utilisation of the isobole methodology to study dietary peptide–drug and peptide–peptide interactive effects on dipeptidyl peptidase IV (DPP-IV) inhibition

“…Similar results have been described where the immunomodulatory properties of an hydrolysate was less than that of its associated isoelectric focusing fractions when tested at the same concentration 26 . This was explained by the fact that 25 some peptides may interact through physicochemical interactions 27 , making them unavailable as bioactive components.…”

Immunomodulatory activities of whey β-lactoglobulin tryptic-digested fractions

“…Curiously, microscopic observation of DR cultures revealed characteristic aggregates that did not appear in other fractions. This finding may be related to the presence of the peptide f(41e60), which has been reported as an aggregating agent (Groleau et al, 2003). Similar to resting cells, no significant proliferative effect was observed with the TH fraction.…”

“…Probably, peptideepeptide interactions could be a potential explanation of why this peptide is surprisingly present in this fraction, since aggregating properties have been reported (Groleau, Morin, Gauthier, & Pouliot, 2003). In fact, this peptide has been shown to interact with other peptides and this could impair the separation of peptide mixtures (Groleau et al, 2003). This peptide was also present in DR and TH samples, but accompanied in this case by a number of other larger, acid and negatively charged peptides.…”

“…Finally, it is interesting to note that the peptide f(15e40), despite its charge and size, was unexpectedly present in the PES-1 fraction, although it was completely absent in PES-5 and HYD-2. Probably, peptideepeptide interactions could be a potential explanation of why this peptide is surprisingly present in this fraction, since aggregating properties have been reported (Groleau, Morin, Gauthier, & Pouliot, 2003). In fact, this peptide has been shown to interact with other peptides and this could impair the separation of peptide mixtures (Groleau et al, 2003).…”

Milk protein hydrolysates activate 5-HT2C serotonin receptors: influence of the starting substrate and isolation of bioactive fractions

“…51,52 Fractions isolated by Mercier et al 52 induced a higher lymphocyte secretion compared to the parent hydrolysate. This was explained by the fact that peptide-peptide interactions (hydrophobic and electrostatic 100 interactions) can occur in milk protein hydrolysates, 69 resulting in lower bioactive potential of hydrolysates compared to fractions, 52 which may have occurred within NaCNH-240 min herein. In addition, enrichment of bioactive peptides upon fractionation could be seen following analysis of the RP-UPLC profiles of 105 these fractions (data not shown).…”