Resumo:
The growing interest in microalgae is due to their photosynthetic characteristics and broad global distribution, making them promise for the production of bioactive compounds with high biological and biotechnological value, applicable in various fields. By modifying the cultivation conditions of these organisms, the production of these compounds can be altered, potentially increasing their efficacy and potential. This study aimed to evaluate the antioxidant activity, phytochemical profile, and phenolic compounds of the microalgae Pyramimonas virginica and Tetraselmis gracilis in response to pH variations (3.0 and 5.0). Antioxidant activity was measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method, while phenol content was determined by the Folin-Ciocalteu method. Toxicity was assessed using Artemia salina, and the phytochemical profile of ethanolic extracts was obtained through qualitative screening. The results showed that microalgae growth was similar for both species; however, those cultivated at pH 3.0 exhibited a significant decrease in optical density, indicating reduced biomass production, leading up to cell death. At pH 5.0, both species showed an increase in optical density comparable to the control (pH 7.0). P. virginica presented a higher yield (0.984 g∙L⁻¹) compared to T. gracilis (0.482 g∙L⁻¹), while the yields for the control were 1.102 g∙L⁻¹ and 1.065 g∙L⁻¹, respectively. In the ethanolic extracts, the antioxidant inhibitory concentration needed to reduce the initial DPPH concentration by 50% (IC50) for P. virginica increased approximately fourfold at pH 5.0 (17.09 mg∙mL⁻¹) compared to the control sample (4.52 mg∙mL⁻¹). For T. gracilis, the IC50 was slightly reduced from 16.7 mg∙mL⁻¹ in the control to 12.57 mg∙mL⁻¹ under acidic cultivation, indicating higher antioxidant activity in this sample. The qualitative phytochemical screening revealed the presence of flavonoids in both species and polyphenols in T. gracilis. Regarding phenolic compounds, P. virginica had the highest content at neutral pH (11.10 ± 0.032 mg GAE/g of extract), while T. gracilis showed an increase in phenolic compound concentration at acidic pH (7.36 ± 0.012 mg GAE/g of extract), corroborating the observed antioxidant activity. In the toxicity test, the ethanolic extracts were not considered toxic to A. salina. These results indicate that the production of bioactive compounds in microalgae can be significantly modulated by cultivation conditions, such as pH, reflecting low toxicity and increased antioxidant potential under low pH conditions.
