Nanoliposomal Encapsulation and Purification of Angiotensin-Converting Enzyme Inhibitor Peptides from <i>Ulva rigida</i>

Angiotensin-converting enzyme inhibitory peptides derived from natural sources may be effective in the treatment of hypertension without causing side effects compared with existing angiotensin-converting enzyme (ACE) inhibitors. Naturally derived antihypertensive peptides are therefore considered a promising alternative for the prevention or treatment of hypertension. Therefore, the study aimed to purify and identify ACE-inhibitory peptides from the green macroalgae Ulva rigida. In addition, the encapsulation of the purified peptides showed the highest ACE-inhibitory activity by chitosan-coated nanoliposomes, and the characterization of nanoliposomes was evaluated. Protein hydrolysates were obtained from U. rigida through enzymatic hydrolysis. The hydrolysates were separated into molecular weights of <3, <5, and <10 kDa through ultrafiltration membrane separation (UFMS). The <3 kDa fraction (UFMS-3) that exhibited the highest ACE-inhibitory activity (77.02%, 1 mg/mL) was purified using ion-exchange chromatography. Fraction-1 (IEC-F1) obtained from the ion-exchange purification showed an impressive 82.03% ACE-inhibitory activity. Moreover, peptide sequences of IEC-F1 were identified by LC-MS/MS, and their bioactive properties were determined in silico. After that, IEC-F1, with a strong ACE-inhibitory activity, was loaded into chitosan-coated nanoliposomes to improve their stability for encapsulation. Physical stability (zeta-potential, polydispersity index, particle size), thermal (DSC) and morphological properties (SEM), and FT-IR analyses were carried out for the characterization of nanoliposomes. Encapsulation efficiency was found to be 92.0 +/- 4.5%. After encapsulation, the ACE-inhibitory activity of IEC-F1 was protected by 37.5%. Overall, the obtained findings indicate that the hydrolysate produced by the successive hydrolysis of U. rigida macroalgae with pepsin and trypsin contains peptides with strong ACE-inhibitory action. Furthermore, the chitosan-coated nanoliposome method was determined to be an effective carrier for the delivery of peptide fractions, showing ACE-inhibitory activity. The formulation of chitosan-coated nanoliposomes for peptide fractions from U. rigida represents an innovative approach that allows the development of functional and stable products.