Biological Properties of Red Macroalgal Protein Hydrolysates and Their Uses as Biopreservatives

In this study, we investigate the effect of different enzyme/substrate ( E / S ) ratios on the antioxidant and antibacterial properties of protein hydrolysates from two unexplored red macroalgae, namely, Sphaerococcus coronopifolius (SCPH) and Gelidium spinosum (GSPH). Antioxidant properties were evaluated using DPPH radical scavenging capacity, reducing power, ferrous ion chelating ability, and total equivalent antioxidant capacity. On the other hand, antibacterial activities were evaluated using agar diffusion and minimum inhibitory concentration (MIC) methods against six bacterial strains ( Listeria monocytogenes , Staphylococcus aureus , Kocuria rhizophila , Micrococcus luteus , Escherichia coli , and Salmonella newport ). The biopreservative effect of SCPH and GSPH on minced meat quality during 11 days of storage at 4°C was also studied focusing on lipid oxidation status and microbial growth. Both protein hydrolysates have considerable antioxidant activities whatever the E / S ratio used, in terms of scavenging DPPH radical (IC 50 ranging from 0.12 to 3.22 mg/mL) and metal chelating activity (IC 50 ranging from 0.15 to 2.24 mg/mL). At 5 mg/mL, the reducing power of SCPH and GSPH varied from 1.16 to 2.87. Moreover, SCPH and GSPH exhibited strong antibacterial activity against all tested bacteria, with MIC values ranging from 1.56 to 25 mg/mL. In addition, the incorporation of SCPH and GSPH into minced beef meat significantly ( p < 0.05) inhibited lipid peroxidation and microbial growth during 11 days of storage at 4°C. At the end of the storage period, the TBARS values measured in the groups treated with 1% ( w / w ) SCPH and GSPH were significantly reduced to 1.36 ± 0.003 and 1.34 ± 0.01 mg MDA/kg meat, respectively. Overall, the results showed that the addition of both protein hydrolysates has a positive effect on meat quality and suggest that SCPH and GSPH can serve as effective natural additives, enhancing the biopreservation and shelf life of refrigerated minced beef.