Exploring the Physicochemical Characteristics of Marine Protein Hydrolysates and the Impact of In Vitro Gastrointestinal Digestion on Their Bioactivity.

Fish protein hydrolysates (FPHs) were obtained from different fish sources using a combination of microbial enzymes. The industrially produced FPHs from blue whiting () and sprat () were compared to freeze-dried FPHs generated in-house from hake () and mackerel () in terms of their physicochemical composition and functionality. Significant differences ( < 0.05) were observed in the protein, moisture, and ash contents of the FPHs, with the majority having high levels of protein (73.24-89.31%). Fractions that were more extensively hydrolysed exhibited a high solubility index (74.05-98.99%) at different pHs. Blue whiting protein hydrolysate-B (BWPH-B) had the highest foaming capacity at pH 4 (146.98 ± 4.28%) and foam stability over 5 min (90-100%) at pH 4, 6, and 8. The emulsifying capacity ranged from 61.11-108.90 m/g, while emulsion stability was 37.82-76.99% at 0.5% (/) concentration. In terms of peptide bioactivity, sprat protein hydrolysate (SPH) had the strongest overall reducing power. The highest Cu chelating activity was exhibited by hake protein hydrolysate (HPH) and mackerel protein hydrolysate (MPH), with IC values of 0.66 and 0.78 mg protein/mL, respectively, while blue whiting protein hydrolysate-A (BWPH-A) had the highest activity against Fe (IC = 1.89 mg protein/mL). SPH scavenged DPPH and ABTS radicals best with IC values of 0.73 and 2.76 mg protein/mL, respectively. All FPHs displayed noteworthy scavenging activity against hydroxyl radicals, with IC values ranging from 0.48-3.46 mg protein/mL. SPH and MPH showed the highest scavenging potential against superoxide radicals with IC values of 1.75 and 2.53 mg protein/mL and against hydrogen peroxide with 2.22 and 3.66 mg protein/mL, respectively. While inhibition of α-glucosidase was not observed, the IC values against α-amylase ranged from 8.81-18.42 mg protein/mL, with SPH displaying the highest activity. The stability of FPHs following simulated gastrointestinal digestion (SGID) showed an irregular trend. Overall, the findings suggest that marine-derived protein hydrolysates may serve as good sources of natural nutraceuticals with antioxidant and antidiabetic properties.