Antioxidant activity of protein hydrolysates of spent Arthrospira maxima biomass prepared with Papain, Alcalase, Trypsin, Protamex 1.6, and Alcalase 2.4 L for 2–10 h hydrolysis based on four different antioxidation assays: (A) scavenging activity of DPPH radicals, (B) scavenging activity of superoxide anion free radicals, (C) scavenging activity of hydroxyl radicals, and (D) total antioxidative capacity (T-AOC) (letters stand for a statistically significant difference with p < 0.05). The error bars represent the standard deviations of triplicates. The hydrolysis conditions are described in Table 1.