Response surface methodology based optimization of biomass and ultrasound assisted extraction and characterization of bioactive compounds from <i>Neochloris</i> sp. isolated from fresh water

In this study, the microalgae Neochloris sp. is isolated from freshwater bodies. To increase the biomass of Neochloris sp. primary optimization studies were done for the selection of suitable carbon and nitrogen sources. Further optimizations were conducted by response surface methodology (Box Behnken method) for increased biomass production. Neochloris sp. grown in the presence of 0.04 g/L sodium acetate, 1.5 g/L urea, 7.5 pH, at 30 °C temperature, showed increased biomass. A second-order polynomial produced satisfactory biomass yield results (P < 0.0001). Results of the predicted and actual response were different, with better residual > 0.02%, and predicted R2 0.9839 and actual R2 0.9928 for biomass, which shows a more reliable model. The bioactive compounds are extracted through Ultra-Sound Assisted extraction from Neochloris sp. and observed through TLC to confirm the presence of carotenoids which separates at a retention factor value of 0.38. A phytochemical test for the extract showed positive results for terpenoids. HPLC was performed for characterization studies which separate at a retention time of 4.171 min. The extract shows maximum DPPH radical scavenging activity of 93%, ABTS of 92% and H2O2 scavenging activity of 64% at 120 µL/mL concentration. From this study, we can conclude that Neochloris sp.is a possible microalgae for producing antioxidants that can be used in the food industry as a natural coloring agent.