In-vitro antioxidant activities of semi - purified methanolic extract of Lyengaria stellata and Padina boergesenii were evaluated using DPPH radical-scavenging activity and reducing power. Total phenolic contents (TPC) and total flavonoid contents (TFC) were also investigated. The acetone fraction of L. stellata contained the highest value (126.04±8.65 mg GAE/g) of TPC, and the highest concentration of TFC (94±0.13 and 82±0.09 mg GAE /g) was obtained in ethanol fractions of Lyengaria stellata and Padina boergesenii, respectively. The highest DPPH scavenging activity (88.5%) was observed in the acetone fraction of L. stellata (1 mg/ml). The most significant reducing power was observed in the acetone fractions of both seaweeds at 100 mg/ml concentration (1.130±0.040 and 0.839±0.010, respectively). Ethanol and acetone fractions of L. stellata showed the greatest antibacterial activity (29.6±0.5 and 28.0±0.7 mm, respectively) against Staphylococcus aureus. The minimum value of MIC was observed in acetone fractions of both seaweeds against S. aureus (50.7 and 50.8 µg/ml), while Salmonella enterica showed the highest resistance to seaweeds extracts according to the– highest MIC values (>200 mg/ml) and the smallest IZ diameters. The extract of both algae showed considerable antioxidant activity according to DPPH radical scavenging activity and reducing power assays.
