Study on in Vitro Stability and Antioxidant Activity of ACE Inhibitory Peptide from Gracilaria lemaneiformis

Gracilaria lemaneiformis were prepared by enzymatic hydrolysis with molecular weight <1 kDa, collecting peptide components by freeze drying and spray drying, measuring the activity retention rate and antioxidant capacity of ACE inhibitory peptides in the in vitro environment. The antioxidant capacity and in vitro stability of peptides were determined by experiments of inhibition of angiotensin converting enzyme activity, total antioxidant capacity, DPPH· scavenging capacity, hydroxyl free radical scavenging capacity and superoxide anion scavenging capacity. The results showed that by using ACE inhibitory activity as indicators, both had good IC₅₀ values (0.62, 0.70 mg/mL) in ACE inhibitory activity. The addition of metal ions (Zn²⁺、Cu²⁺) were both promoted inhibitory activity retention, (Al³⁺、K⁺、Fe³⁺) were retained the ACE inhibitory activity of GLP-F and GLP-S, Ca²⁺reduced the ACE inhibitory activity of both. With the increase of NaCl concentration, the ACE inhibitory activity was reduced of GLP-F and GLP-S; under high sugar concentration, GLP-F was better retained, and GLP-S activity was significantly increased(P<0.05). With strong acid and alkali, GLP-F activity retention decreased by 5%, GLP-S inhibitory activity remained unchanged with pH 4~10. Below 40 ℃, the ACE inhibitory activity was stabled of GLP-F and GLP-S. Simulation the digestion of gastrointestinal tract, GLP-F belonged to pro-drug type, GLP-S belonged to true inhibitor type. GLP-F and GLP-S suited for storage at −20 °C, GLP-F activity retention decreased to 40.67% stored at 4 ℃ until 14 d. The results of above antioxidant tests indicated that GLP-S had superior in terms of total antioxidant activities, DPPH· free radicals, ·OH and O₂⁻· than GLP-F. Therefore, the stability of GLP-F polypeptide in lowering blood pressure activity in vitro had better than that of GLP-S, and GLP-S had more effective than GLP-F in anti-oxidation. Gracilaria lemaneiformis polypeptide providing theoretical reference for the development of natural antihypertensive peptides and antioxidant peptides.