Whey-Derived Antihypertensive Peptides Produced by Proteinase K Hydrolysis and Fermentation

Abstract Whey accounts for up to 90% of the total milk volume and is often discarded directly into drains. Due to its rich protein composition—particularly β-lactoglobulin, α-lactalbumin, and serum albumin—whey has been recognized as a valuable source of bioactive peptides, many of which exhibit antihypertensive properties via ACE inhibition. In this study, whey protein concentrate (WPC-80) was subjected to controlled enzymatic hydrolysis using Proteinase K, a broad-specificity serine protease known for its ability to cleave peptide bonds adjacent to hydrophobic and aromatic amino acids—residues frequently found in ACE-inhibitory peptide sequences (e.g., IPP, VPP). This hydrolysis yielded a degree of hydrolysis reflected by 29.98 µg/mL of free amino groups, generating a pool of intermediate peptides and oligopeptides with exposed C- and N-termini. Subsequently, three fermentations were performed using Streptococcus thermophilus SY-102 and Lactobacillus rhamnosus GG—individually and in co-culture—to further process the hydrolysate. Lactic acid bacteria possess cell-envelope proteinases (e.g., PrtS in S. thermophilus and PrtP in L. rhamnosus) and intracellular peptidases that can selectively hydrolyze larger fragments into smaller, bioactive peptides (often 2–12 amino acids), enhance peptide stability, and modify peptide sequences to optimize ACE-binding affinity (e.g., by enriching C-terminal tripeptides with Pro or aromatic residues). The antihypertensive capacity was evaluated via in vitro ACE inhibition assay. Fermentation with S. thermophilus SY-102 achieved the highest ACE inhibition (81.96%), likely due to its robust proteolytic system and preferential release of potent tripeptides such as IPP/VPP. In contrast, the co-fermentation showed significantly lower inhibition (19.73%), possibly due to competitive or antagonistic interactions between the strains altering peptidase expression, substrate preference, or peptide degradation profiles. These results demonstrate that a sequential strategy—initial hydrolysis with Proteinase K to unfold and partially cleave whey proteins, followed by targeted microbial fermentation—synergistically enhances the generation and/or preservation of ACE-inhibitory peptides, offering a promising valorization route for whey byproducts. Graphical Abstract