The effect of pH and temperature on growth, the antioxidants, phenols and flavonoids in Scenedesmus sp. microalgae

Microalgae are one of the rich sources of natural antioxidants in various applications in the food and pharmaceutical industries. In this study, the effect of temperature stress (23˚c, 28˚c, 33˚c) and pH (5, 7, 8, 9) on antioxidant activity, phenolic and flavonoids content and on the amount of colorants in the microalgae Scenedesmus sp. was studied. Environmental conditions for all treatments 12:12 light:dark, continuous aeration, and treatment time of 16 days. Extracting compounds with methanol solvent, and antioxidant activity by FRAP, phenolic content by Folin-Ciocalteu , the content of flavonoids was measured using a representative of aluminum chloride and chlorophyll content a and b and carotenoid . The results showed that, the best conditions for antioxidant activity and flavonoid production occurred at high pH (8 and 9) and low temperature (23˚c). Concerning phenolic content, the results indicated that temperature (23˚c) plays a more effective role than pH in a significant increase (p<0.05) in phenolic content (7/53 ± 0/06 mg GAE /g DW), and pH caused a significant decrease (p<0.05) in phenolic content compared to control. Also, although pH and temperature stress did not affect the amount of chlorophyll b, but in general, the results indicate that pH and temperature treatment can affect the production of antioxidants in the Scenedesmus sp. microalgae.