Antibacterial and antioxidant activities of differential solvent extractions from the green seaweed Ulva intestinalis

Abstract

The green algae (Enteromorpha spp.) is widely distributed in the southern coast of Thailand. Antibacterial, total phenolic, and antioxidant activities of crude extracts from Ulva intestinalis (E. intestinalis) with differential solvent extractions were investigated. Alga extracts were prepared by maceration with methanol, ethanol, dichloromethane, and hexane. Only the hexane extract had significant antibacterial activities for Gram-positive bacteria but not Gram-negative bacteria. The lowest minimal inhibitory concentrations of the hexane extract against Bacillus cereus TISTR 687, Staphylococcus aureus ATCC 29213, and methicillin-resistant Staphylococcus aureus 001 R (MRSA) were 256 µg/ml. Pore formation was observed on the cell surface of B. cereus treated with the hexane extract. Among these extracts, the highest inhibition radical scavenging effects on 2,2-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) activities were observed in the dichloromethane extract with IC50 = 0.92 mg/ml and 1.50 mg/ml, respectively. The highest phenolic content index was observed with the dichloromethane extract as 197 ± 16 mg gallic acid equivalents/g extract and was significantly higher than those of other extracts (p < 0.05). The results indicated that this edible seaweed possesses bioactive compounds that could be further explored for future applications in medicine, dietary supplements, cosmetics, and food industries.