Protein Hydrolysates and Ultrafiltration Fractions Obtained from Krill (Euphausia superba): Nutritional, Functional, Antioxidant, and ACE-Inhibitory Characterization

Krill (Euphausia superba) was hydrolyzed by proteolytic enzymes in order to produce multifunctional bioactive peptides, and their functional properties were evaluated. Krill protein hydrolysate (KPH) by pepsin with 4-h hydrolysis showed the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging and angiotensin I converting enzyme (ACE) inhibitory activities. The solubility and foaming properties of KPH were higher than those of the unhydrolyzed krill protein at a wide range of pHs. KPH was further fractionated based on molecular weight. The 1- to 3-kDa peptide fraction exhibited the highest DPPH scavenging activity (IC50 value of 0.5 mg/mL), oxygen radical absorbance capacity (497.39 ± 4.31 µM TE/mg fraction), 2,2-azino-bis(3-ethylbenzthiazoline)-6-sulfonic acid cation radical scavenging activity (48.41 ± 0.23 µM TE/mg fraction), and reducing power (110.40 ± 2.07 µM TE/mg fraction). However, the < 1-kDa peptide fraction exhibited a higher ACE inhibitory activity than that of other fractions. The 1- to 3- and < 1-kDa peptide fractions are rich in aromatic and hydrophobic amino acids, respectively.