Improved emulsifying properties of β-barrel domain peptides obtained by membrane-fractionation of a limited tryptic hydrolysate of β-lactoglobulin

Fragments of the β-barrel domain of β-lactoglobulin were obtained by membrane fractionation of a limited proteolysate prepared with an immobilized trypsin bioreactor. Analysis of this fraction by size-exclusion chromatography under physiological conditions indicated that the fraction contained a predominant peptide (50%) with a size of 8400 Da and several other peptides with sizes ranging from 2000 to 30 700 Da. Analysis of reductively denatured peptides by sodium dodecyl sulfate polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol indicated the presence of a major peptide with a size of 6400 Da, suggesting that a small peptide was linked to the 8400-Da peptide by a disulfide bond. Comparison of the surface and emulsifying properties of the peptide fraction with those of intact β-lactoglobulin indicated that the domain peptides have a lower surface hydrophobicity and a slightly higher surface and interfacial tension. Furthermore, the emulsifying activity index for the domain peptides was twofold larger than that of the intact protein. Examination of the emulsion by scanning electron microscopy revealed that the oil droplets formed with the domain peptides were smaller than those formed with intact protein.