Diplodus Protein Hydrolysates: Antioxidant and Antibacterial Properties and Identification of Biopeptides

Diplodus annularis is an underutilized protein-rich fish resource which is sold at a low cost. In this work, the valorization of Diplodus proteins as a source of bioactive protein hydrolysates is proposed.

Hydrolysates from Diplodus proteins were prepared using alcalase and savinase enzymes at optimal conditions and their antioxidant and antibacterial activities were evaluated. The hydrolysate that revealed the highest biological properties was fractionated by RP-HPLC and peptide fractions implied in bioactivity were determined using a peptidomic approach.

The antioxidant properties of the hydrolysates were evaluated using various in vitro assays. The hydrolysate generated by savinase (DPH-S) generally exhibited a greater antioxidant activity across all the considered methods, in terms of ferrous chelating activity ( \({IC}_{50}\) ${\mathit{IC}}_{50}$ =2.19 mg mL⁻¹), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability ( \({IC}_{50}\) ${\mathit{IC}}_{50}$ =3.76 mg mL⁻¹) and reducing power activity (1.92 ± 0.12). Moreover, the alcalase-generated hydrolysate (DPH-AL) exhibited the highest β-carotene bleaching inhibitory effect ( \({IC}_{50}\) ${\mathit{IC}}_{50}$ =4.41 mg mL⁻¹). The antibacterial activities of hydrolysates were also assessed. DPH-S exhibited the most important inhibitory effects against five strains of bacteria. It was chosen to undergo fractionation and purification by reverse phase-high performance liquid chromatography (RP-HPLC) into ten fractions and then identified by peptidomics approach. F4 which contained 408 peptides with molecular mass lower than 3000 Da, displayed the highest antioxidant activites and had significantly the highest percentage of bacteria inhibition against bacterial species (p < 0.05).

Our results revealed that DPH-S and its peptide fractions could be a new potential source for preparing natural antioxidants and antibacterials applied in food, pharmaceutical and cosmetic preparations.