Antioxidant and antibacterial properties of red macroalgae protein hydrolysates and their potential use as bio-preservatives ffor beef

Recently, numerous bioactive peptides derived from algal protein hydrolysates with potential nutritional and health benefits have been isolated from macro- and microalgae. In this study, we investigate the effect of different Enzyme/Substrate (E/S) ratios on the antioxidant and antibacterial properties of two unexplored red macroalgae (Sphaerococcus coronopifolius and Gelidium spinosum) protein hydrolysates, namely SCPH and GSPH, respectively. Their antioxidant properties were evaluated using four assays, including their scavenging capacity ffor DPPH radicals, reducing power, ferrous ion-chelating ability, and total equivalent antioxidant capacity. For antibacterial property evaluation, agar diffusion and minimum inhibitory concentration (MIC) methods were applied to six indicator bacterial strains (Listeria monocytogenes, Staphylococcus aureus, Kocuria rhizophila, Micrococcus luteus, Escherichia coli, and Salmonella Newport). Then, their effects on the quality of minced meat during 11 days of storage at 4 °C were evaluated. Lipid oxidation status (malonaldehyde, metmyoglobin, and heme iron contents) and bacteriological (total viable, coliform, yeast, and mold counts) evaluations were made in minced beef under refrigerated conditions. The results demonstrated the high antioxidant activities of both hydrolysates, whatever the E/S ratio. Particularly, DPPH radical scavenging activities ranging from 90.84% to 100% were seen, especially at an E/S ratio of 1/2 (w/w). Moreover, these peptidic hydrolysates exhibited important in vitro antibacterial activities against all the tested bacteria, with MIC values of 1.56-25 mg/mL. In addition, lipid peroxidation and microbial growth were significantly reduced (p < 0.05) following the incorporation of SCPH and GSPH into the minced meat during 11 days of storage at 4 °C. Overall, these results suggest that both protein hydrolysates demonstrate a positive effect on quality bio-preservation and the extended shelf life of refrigerated minced beef. SCPH and GSPH could be considered natural preservative additives that could be used to prevent unwanted changes to food, including meat and meat products, during storage.