Effect of high-pressure treatment on the tryptic hydrolysis of bovine β-lactoglobulin AB

The effects of high-pressure treatment on the tryptic hydrolysis of bovine beta-lactoglobulin AB were studied. Isostatic pressure (100-800 MPa, 15 min) was applied to the protein substrate prior to its hydrolysis, as well as following its digestion at atmospheric pressure. Hydrolysis (100 min at 40 degrees C) was also conducted under high pressure (100-400 MPa). To characterize the hydrolysates on a molecular level, peptide mapping by RP-HPLC was coupled on-line to detection by electrospray ionisation mass spectrometry. Under pressures up to 400 MPa, tryptic hydrolysis of beta-lactoglobulin was increased with an optimum at 300 MPa. Analysis of the digests showed that the enhanced hydrolysis was due to accelerated breakdown of large intermediate hydrolysis products into final tryptic peptides. Among others, it was found that under these conditions the Tyr20-Ser21 peptide bond splitting was complete, resulting to entire conversion of Val15-Arg40 intermediate into Val15-Tyr20 and Ser21-Arg40 end-products. Increasing pressures applied during pre-pressurization (100-800 MPa) resulted in small but progressive reduction in residual intact beta-lactoglobulin, but no change in the peptide profile of the hydrolysates obtained was observed. Similar to this, post-pressurization of the tryptic hydrolysate had no measurable effect on the peptide profiles. (C) 1998 Elsevier Science Ltd. All rights reserved.