Thermal stabilization of beta-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 beta-lactoglobulin (beta-lg), a mixture of beta-lg and nonfractionated hydrolysate, and beta-lg:peptide mixtures (3:1 weight ratio) were solubilized in acetate or phosphate buffers, and their heat denaturation profiles between 25 and 100 degrees C were studied over the pH range of 4.6-8.0. Thermal denaturation of individual beta-lg was greatly influenced by pH, its denaturation temperature (T-D) decreasing from 77.4 to 66.9 degrees C for pH 4.6-8.0, respectively. The addition of nonfractionated hydrolysate to beta-lg accentuated this effect, whereas T-D and heat enthalpy (Delta H-D) were increased in the presence of the peptide fractions. Fractions obtained by AEC (F-2-F-8) thermally stabilized beta-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 degrees C over the pH range under study. The binding of peptides to beta-lg, possibly via ionic or hydrophobic interactions, may stabilize beta-lg structure against heat treatment.