OXIDATIVE STRESS AND ANTIOXIDANT ACTIVITIES OF Parachlorella kessleri AT DIFFERENT GROWTH PHASES

Parachlorella kessleri is a potential source of natural antioxidants. However, limited research has been undertaken on P. kessleri's antioxidants, especially during its cultivation period. This study aims to compare the oxidative stress and antioxidant activities in P. kessleri throughout different growth phases. It was grown in F/2 medium supplemented in natural seawater (30 ppt) under continuous light at 242C for 24 days. The oxidative stress responses (hydrogen peroxide, H 2 O 2 and malondialdehyde, MDA) and antioxidant assays (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX and glutathione reductase, GR) were assessed at five distinct phases; lag (day 1), exponential (day 4), early stationary (day 8), mid stationary (day 16), and death (day 24). Significant differences were observed for H 2 O 2 during the exponential to stationary phases, but MDA was highest at the death phase. SOD, CAT, and APX activities were enhanced during the lag, exponential, and early stationary phases, respectively. GR reached the maximum activity during the exponential and early stationary phases. The results revealed that these oxidative stress biomarkers and antioxidant activities responded differently throughout growth phases, substantially at the exponential and early stationary phases. These findings are essential in selecting the best growth phase for further enhancements of P. kessleri's antioxidants.