Preparation and Characterization of Ultrasound-Assisted Novel Peptide–Calcium Chelates from Nannocholoropsis oceanica

Abstract

Novel peptide–calcium chelates have been successfully developed using ultrasound technology from Nannochloropsis oceanica (N. oceanica), and they have been found to be superior calcium supplements as natural bioactive peptide–calcium chelates. The study has provided a comprehensive understanding of the interaction between Ca²⁺ ions and peptides or amino acids. Under optimal conditions, a calcium chelation rate of 61.89 ± 0.12%, a calcium chelation activity of 9.08 ± 0.15%, and a calcium chelation yield of 65.57 ± 0.19% were achieved. Most peptides and peptide–calcium chelate have a molecular weight below 1500 Da. Characterization tests confirmed the production of new complexes as chelates, and different spectral and signal analyses by FTIR, fluorescence, UV, XRD analysis, and zeta potential, collaboratively, confirmed that metal ions combined with amino, carboxyl, and other active chelating groups in N. oceanica peptides form metal chelates and generate new crystal structure interactions within the chelates. In addition, morphological analysis the peptide–calcium chelate was depicted through SEM and AFM images implied that folded, aggregated, and tightly packed structures were formed in the peptide–calcium chelate. The calcium content in chelates up to 4.48% (0.58% in peptides) suggested the interaction of calcium with peptides to form chelates. Besides, peptide–calcium chelates are relatively stable under high temperature, pH, and digestive conditions in stage of gastric digestion tract, indicating that they can serve as an efficient calcium supplement. These findings underscore the potential development of functional foods from N. oceanica peptides, offering an alternative to conventional calcium supplements. Furthermore, the results of this study can provide new directions for the high-value utilization and development of N. oceanica protein and provide a theoretical basis for N. oceanica peptide as a functional component of calcium supplements.