Thermal Stabilization of β-Lactoglobulin by Whey Peptide Fractions

Tryptic hydrolysate of whey protein isolate (WPI) was fractionated by anion-exchange chromatography (AEC) and hydrophobic interaction chromatography (HIC). Individual β-lactoglobulin (β-lg), a mixture of β-lg and nonfractionated hydrolysate, and β-lg:peptide mixtures (3:1 weight ratio) were solubilized in acetate or phosphate buffers, and their heat denaturation profiles between 25 and 100 °C were studied over the pH range of 4.6−8.0. Thermal denaturation of individual β-lg was greatly influenced by pH, its denaturation temperature ( T D ) decreasing from 77.4 to 66.9 °C for pH 4.6−8.0, respectively. The addition of nonfractionated hydrolysate to β-lg accentuated this effect, whereas T D and heat enthalpy (Δ H D ) were increased in the presence of the peptide fractions. Fractions obtained by AEC (F 2 −F 8 ) thermally stabilized β-lg as a function of their increasing ionic charge, and this effect became more important as the pH was raised from 4.6 to 8.0. The results obtained with HIC fractions (F A, F B, and F D ) showed a T D of 78−80 °C over the pH range under study. The binding of peptides to β-lg, possibly via ionic or hydrophobic interactions, may stabilize β-lg structure against heat treatment.