Optimization of antioxidant potential of Aspergillus terreus through different statistical approaches

A three-step optimization strategy, which includes a one-factor-at-a-time classical method and different statistical approaches [Plackett-Burman design and RSM (response surface methodology)], were applied to optimize the antioxidant potential of Aspergillus terreus. Antioxidant activity was assayed by different procedures and compared with TPC (total phenolic content). Primarily, different carbon and nitrogen sources were screened by classical methods, which revealed sucrose and NaNO3 to be the most suitable. The significance of the components of Czapek Dox's medium with respect to antioxidant activity was evaluated with the Plackett-Burman design, which supported sucrose and NaNO3 to be the most significant. In a second step, sucrose and NaNO3 along with temperature were further taken as three variables for RSM to study their interaction. Response surface analysis showed 4% sucrose, 0.1% NaNO3 and an incubation temperature of 30 °C to be the optimal conditions. Under these conditions, the antioxidant potential assayed through the different procedures was 88.1, 74.9 and 70.2% scavenging effect for DPPH (1,1-diphenyl-2-picryl hydrazyl) radical, ferrous ion and nitric oxide ion respectively. The reducing power showed an absorbance of 2.0 with 71.5% activity for the FRAP (ferric reducing antioxidant power) assay. TPC under different physio-chemical conditions and antioxidant potential under various assay procedures correlated positively.