Study on preparation of ACE inhibitory peptide and Zn²⁺ binding activity of tuna skin

Tuna skin is protein-rich and a promising raw material for bioactive peptide production. To promote the high-value utilization of tuna processing by-products and provide a reference for the development of food-derived angiotensin converting enzyme (ACE) inhibitors, we used the skin of bigeye tuna (Thunnus obesus) as the raw material, prepared tuna skin angiotensin converting enzyme inhibitory peptides (TSAIP) via enzymatic hydrolysis, and analyzed the correlation between their antioxidant activity and zinc ion (Zn²⁺)-binding activity. Results show that the product (TSAIP) obtained by trypsin hydrolysis for 4 h exhibited the highest ACE inhibition (60.00±6.70)% and Zn²⁺-binding ability, with an ABTS radical scavenging rate of (68.51±1.80)%. Correlation analysis reveals a significant positive association between ACE inhibitory activity and both Zn²⁺-binding capacity and ABTS scavenging rate (p<0.05). Glycine, proline, and glutamic acid were the three most abundant amino acids in TSAIP. Hydrophobic amino acids constituted 50.00% of the total content. The binding of TSAIP to Zn²⁺ induced conformational changes in its structure, resulting in increase in ultraviolet absorption, red shift in the maximum absorption wavelength, and decrease in intrinsic fluorescence intensity. The study demonstrates that tuna skin is a good protein source for the preparation of ACE inhibitory peptides, and the ACE inhibitory activity of active TSAIP is closely related to its antioxidant activity, Zn²⁺-binding capacity, and structural characteristics.