Hydrolysis of Whey Protein Isolate with Bacillus licheniformis Protease: Aggregating Capacities of Peptide Fractions

In a previous study, peptides aggregating at pH 7.0 derived from a whey protein hydrolysate made with Bacillus licheniformis protease were fractionated and identified. The objective of the present work was to investigate the solubility of the fractionated aggregating pepticles, as a function of concentration, and their aggregating capacities toward added intact proteins. The amount of aggregated material and the composition of the aggregates obtained were measured by nitrogen concentration and size exclusion chromatography, respectively. The results showed that of the four fractions obtained from the aggregating pepticles, two were insoluble, while the other two consisted of 1:1 mixture of low and high solubility pepticles. Therefore, insoluble pepticles coaggregated, assumedly via hydrophobic interactions, other relatively more soluble pepticles. It was also shown that aggregating pepticles could aggregate intact protein nonspecifically since the same peptides were involved in the aggregation of whey proteins, beta-casein, and bovine serum albumin. Both insoluble and partly insoluble pepticles were required for the aggregation of intact protein. These results are of interest for the applications of protein hydrolysates, as mixtures of intact protein and pepticles are often present in these applications.