Antioxidant Activity of Peptides Embedded in Potato, Seaweed, Rubisco and Single Cell Proteins

Sustainable eating habits have increased the demand for alternative sources of functional and natural ingredients such as plant and microbial based peptides with antioxidant activity. For some of these sources (potato, seaweed, rubisco and single cell proteins), we have used bioinformatics and proteomics to identify and predict embedded peptides with good radical scavenging and metal chelating activities. Proteomics was also used to confirm that selected peptides are abundant in their parent proteins. The objectives of this study were (i) to screen in-vitro antioxidant activity of synthetic peptides that are predicted to be good antioxidants and (ii) to evaluate the ability of these peptides to retard lipid oxidation in 5% fish oil-in-water emulsions. DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity was measured to evaluate the in vitro antioxidant efficacy to scavenge free radicals. It was found that some of the peptides were indeed good radical scavengers (IC50: 2-6 mM) as predicted. Ferrozin method was used for metal chelating activity; however, solubility issues resulted in unreliable results. Based on the highest in vitro radical scavenging activity, bioinformatics prediction, abundancy of peptides in the parent protein and their potential for being released by trypsin, 11 peptides were selected for further validation of their ability to prevent lipid oxidation in 5% fish oil-in-water emulsions. Iron-mediated emulsions were produced using 1 wt.% Tween 20 and 0.05 wt.% synthetic peptides at pH 7 and the oxidative stability was assessed by determining the formation of primary oxidation products, the consumption tocopherols, and the development of volatile oxidation products during 8 days of storage. Additionally, physical stability was also investigated with zeta potential and droplet size distribution analyses. Results showed that peptides from all sources improved the oxidative stability of the emulsions compared to the control, without changing the physical stability largely.