In vitro antioxidant and antibacterial activities of aqueous extract of microalgae strain MRB-1, MRB-2, and MRB-3

Abstract

The awareness growth of human health encourages market demand of functional food. Microalgae are promoted as natural resources for functional food, food additives and food preservatives, considering their metabolites and nutrient-rich components with diverse pharmacological activities. This study aims to evaluate the phytochemicals, antioxidant, and antibacterial activities of aqueous extracts of microalgae strain MRB-1, MRB-2, and MRB-3. The morphological surface of microalgae cells was analyzed using Scanning Electron Microscopy (SEM). The metabolites of the extract were conducted using Liquid Chromatography-High Resolution Mass Spectroscopy (LC-HRMS) with positive and negative ion modes. In addition, the antioxidant activity was evaluated using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and the antibacterial activity was assessed using the agar disk-diffusion method against gram-positive bacteria (Staphylococcus aureus ATCC 25923) and gram-negative bacteria (Escherichia coli ATCC 8739). The total phenolic contents (TPC) of the extract was determined using the Folin-Ciocalteu assay. The result revealed that the aqueous extract of microalgae strain MRB-1 had the highest scavenging activity toward DPPH radicals with a value of 24.33±1.44% at 0.8 mg/mL. This data was in accordance with the TPC of the extract, whereas the highest TPC was also obtained from strain MRB-1 extract (17.73±0.64 mg GAE/g extract). Meanwhile, the MRB-2 extract had the highest inhibition activity against S. aureus, with a value of 11.78±2.06 mm at 18 mg/mL. The results of this study indicated that microalgae from the peatlands potentially benefit to human health as a natural antioxidant and antibacterial source.