Fermentation of whey protein concentrate by Streptococcus thermophilus strains releases peptides with biological activities

Cheese whey is the principal by-product of cheese making and is perceived as an environmental pollutant. Different technological procedures have been applied to convert whey into value-added products including whey protein concentrate (WPC). In the present study, 2 Lactobacillus helveticus strains and 5 Streptococcus thermophilus strains, isolated from natural whey starter used in Parmigiano Reggiano production, have been evaluated for their capacity to ferment WPC and to release bioactive peptides. WPC fermented with S. thermophilus RBC06 showed the highest antioxidant activity as well as angiotensin-converting enzyme- and dipeptidyl-peptidase-IV-inhibitory activities followed by WPC fermented by S. thermophilus RBC20 and RBN16. An untargeted peptidomics approach was applied to profile the peptides released after WPC fermentation. Several bioactive peptides, mainly angiotensin-converting enzyme inhibitors, were identified and the anti-hypertensive lactotripeptides valine-proline-proline (VPP) and isoleucine-proline-proline (IPP) were quantified. S. thermophilus RBC06 produced the highest amount of VPP (12.80 ± 0.45 mg/L) whereas the highest quantity of IPP (0.56 ± 0.02 mg/L) was detected in WPC fermented with S. thermophilus RBN16. The present study paved the way for the further exploitation of S. thermophilus RBC06 as new bioactive-peptide producer and for the application of WPC hydrolysates as additives for designing whey-based beverages with improved healthy properties.