Increasing Antihypertensive (ACE Inhibitory) and Antioxidant Activity (DPPH, ABTS and FRAP) Potentials of Spirulina platensis Protein by Proteolytic Hydrolysis

In recent years there is increasing interests on Microalgae as natural sources of bioactive compounds capable of addressing growing nutritional and health challenges. These bioactive constituents, often extracted through biotechnological approaches, have shown therapeutic potential against various diseases. In the present study, dried Spirulina platensissuspended in water was hydrolysed by using gastric (pepsin) and intestinal (trypsin) enzymes for two hours. Additionally, in model gastrointestinal digestion, the pepsin-treated hydrolysate underwent a second enzymatic treatment with trypsin under the same conditions. The obtained protein hydrolysates were evaluated for their angiotensin-I-converting enzyme (ACE) inhibitory activity and antioxidant capacity. The results showed that enzymatic hydrolysis significantly enhanced the bio-functional properties of Spirulina proteins. The degree of hydrolysis (DH) was measured as 2.65% for the untreated sample (PT0), 11.33% for the pepsin hydrolysate (P120), 11.13% for the trypsin hydrolysate (T120), and 13.18% for the sequential hydrolysate (PT240). ACE inhibition rates were determined as 92.40%, 89.96%, 94.81%, and 95.53% for PT0, P120, T120, and PT240, respectively. The IC50values, indicating the protein concentration required to inhibit 50% of ACE activity, were 2.92, 0.68, 0.79, and 0.51 mg protein/mL for PT0, P120, T120, and PT240, respectively. The lower IC₅₀ value of PT240 indicated a stronger ACE inhibitory effect. Antioxidant analyses further supported the enhanced bioactivity of sequential hydrolysates. PT240 exhibited the highest values in all antioxidant assays: DPPH (0.91 mg Trolox equivalents/g DW), ABTS (3.47 mg TE/g DW), FRAP (3.92 mg FeSO4·7H2O/g DW), and total phenolic content (2.87 mg GAE/g DW). In conclusion, enzymatic hydrolysis improved the ACE inhibitory and antioxidant properties of S. platensis protein, with sequential hydrolysis by pepsin and trypsin yielding the most pronounced bioactive effects.