Techno-functional, biological and structural properties of Spirulina platensis peptides from different proteases

This study focused on the effects of different proteases (alcalase, trypsin, pancreatin, and pepsin) on amino acid composition (AAC) and nutritional, techno-functional, antioxidant, structural, and antibacterial properties of Spirulina (SP) protein and its hydrolysates (SPHs). Evaluation of AAC, including essential (30 %), hydrophobic (44 %), and antioxidant (17 %) types, as well as protein efficiency ratio (PER 2.45) indicated the potential of SP and SPHS as the sources of antioxidants with good nutritional and digestibility properties. Enzymatic hydrolysis improved the techno-functional properties (solubility, emulsion, foaming, and water/oil holding capacities). The highest antioxidant activity of SP and SPHs, including Trolox equivalent antioxidative capacity (1.47-2.56 mM), DPPH (24.8-68.6 %), hydroxyl (36.5-76.2 %), nitric oxide (9.1-28.5 %), reducing power (0.73-1.16), total antioxidants (0.87-1.85), and chelation of iron (42.7-73.5 %) and copper (18.5-49.5 %) transition metals were affected by the type of enzymes and the concentration of peptides. Thermal and acidic conditions led to extensive changes in secondary structures (amide A and amides I, II, and III regions), unfolding, and acceleration of protein aggregation. Enzymatic hydrolysis improved the retention of antioxidant activity at different temperatures and acidic conditions. The results of antibacterial tests revealed good activity of alcalase-hydrolyzed protein in growth inhibition of Escherichia coli (14.7 mm) and Bacillus cereus (11.6 mm). Finally, the results of this study demonstrate the usability of SPH in various functional food formulations (acidic and alkaline) as well as in processed and cooked foods.