Influence of high-pressure homogenization on structural properties and enzymatic hydrolysis of milk proteins

This study investigated the effects of HPH processing parameters on the conformational structure of bovine serum albumin (BSA) and whey protein isolate (WPI). BSA and WPI dispersions (1% w/v in phosphate buffer, pH = 7.5) were treated in a bench-scale HPH unit at different pressures (100, 150, 200 MPa) and number of passes (1, 2, 3, 5). The modifications of proteins' primary structure (carbonyl groups), secondary structure (α-helix, β-sheet, turn), tertiary and quaternary structure (free -SH groups) were analyzed together with their particle size distribution (PSD). HPH-assisted hydrolysis with trypsin and α-chymotrypsin was performed (200 MPa, 1 pass). Hydrolysis degree and molecular weight distribution of peptides were determined and compared with those of untreated protein dispersions. HPH treatments did not affect proteins' primary structure while slight modifications of secondary structure were detected. Interestingly, free - SH groups in BSA increased with increasing the pressure due to partial unfolding, while decreased in WPI, possibly due to disaggregation and compaction of native WPI aggregates. HPH pre-treatment allowed enhancing BSA hydrolysis reaction rate, while the compaction of WPI aggregates caused a reduced hydrolysis extent. In conclusion, HPH caused an appreciable modification of protein conformation and affected the degree of enzymatic hydrolysis.