Production of bioactive proteins and peptides from the diatom Nitzschia laevis and comparison of their in vitro antioxidant activities with those from Spirulina platensis and Chlorella vulgaris

Summary This research focuses on green production of bioactive proteins and hydrolysates from Nitzschia . A comparison of antioxidant activities was established between protein extracts and hydrolysates from Nitzschia and two other well‐known microalgae, chlorella and spirulina. Protein hydrolysates from these microalgae were produced using Alcalase ® , Flavourzyme ® and Trypsin. The hydrolysis process enhanced the antioxidant activities in general, especially those obtained using Alcalase ® . Nitzschia showed the highest ( P  < 0.05) total phenolic content/reducing capacity (2.4 ± 0.02 mg GAE /100 g) after 90 min of hydrolysis with Alcalase ® . The ABTS [2,2′‐Azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid)] radical scavenging activity (66.77 ± 0.00%) was highest ( P  < 0.05) after 120 min of hydrolysis, but DPPH (2,2‐Diphenyl‐1‐picrylhydrazyl radical) was low (29.59 ± 0.02%). A correlation between ABTS activity and total phenolic contents was the highest ( P  < 0.05) for protein hydrolysates from all three organisms using Alcalase ® , but superoxide anion radical scavenging activity was intermediate for Nitzschia . Therefore, Nitzschia protein hydrolysates have the potential to be used as antioxidants.