Enzyme-induced gelation of whey proteins

Extensive enzymatic hydrolysis of whey proteins in the presence of Alcalase leads to the formation of a gel. This creates a hurdle in the production of whey protein hydrolysates used in applications such as sports nutrition and hypoallergenic infant formulas. The first objective of this study was to compare enzyme-induced gelation of extensively hydrolyzed whey proteins by Alcalase with the plastein reaction by determining the types of interactions. The average chain length of the peptides did not increase during hydrolysis and reached a plateau after 30 min to be about 4 residues, suggesting that the gel was formed by small molecular weight peptides held together by non-covalent interactions. The enzyme-induced gel network was stable over a wide range of pH and ionic strength, and therefore showed some similarities with the plastein reaction. Disulfide bonds were not involved in the gel network. Peptides released were characterized in order to better understand this gelation phenomenon. The apparent molecular mass distribution indicated that aggregates were formed by small molecular mass peptides (<2,000 Da). One hundred and thirty peptides with varying lengths were identified by reversed-phase high performance liquid chromatography coupled with electrospray ionization mass spectrometry. Most peptides had an average hydrophobicity of 1--1.5 kcal/residue and a net charge of 0 at the pH where gelation occurs (6.0). Therefore, intermolecular attractive force such as hydrophobic interaction suggests the formation of aggregates that further leads to the formation of a gel.;The very complex peptide system identified previously for whey proteins was simplified by using beta-lactoglobulin. Dynamic rheology, aggregation measurements, isoelectrofocusing as well as chromatography and mass spectrometry were used to understand the gel formation. A transparent gel suggesting a fine-stranded network is formed above a critical concentration of peptides while non-covalently linked aggregates appear with increasing time of hydrolysis. Nineteen main peptides were identified with molecular weight ranging from 265 to 1485 Da. Only one fragment came from a beta-sheet rich region of the beta-lactoglobulin molecule and a high proportion of peptides had proline residues in their sequence.