Potential of red, brown, and green macroalgae from Dato Beach, Majene, Indonesia as natural food preservative

Macroalgae is one of the natural resources present in Indonesian coastline areas specifically in Dato Beach, Majene, South Sulawesi. The abundance of macroalgae found in Dato Beach can be utilized in various sectors including health, cosmetics, and food. The aim of this study was to investigate the secondary metabolites of three types of macroalgae in Dato Beach and their potential to inhibit the growth of pathogenic bacteria in food. The three macroalgae utilized in this study were Turbinaria decurrens (brown algae), Galaxaura rugosa (red algae), and Halimeda opuntia (green algae) representing the three groups of macroalgae based on their dominant pigments. Four types of pathogenic bacteria namely, Staphyloccus aureus and Bacillus cereus as Gram-positive bacteria plus Salmonella typhi and Escherichia coli as Gram-negative bacteria were collected from the Biology Laboratory at Universitas Sulawesi Barat, as these bacteria are commonly responsible for food spoilage. The study began with a sampling of macroalgae, followed by cleaning and drying, and subsequently extraction using methanol as the solvent. Methanol was chosen as the universal solvent for its ability to extract both polar and nonpolar components. Phytochemical screening was carried out to test for the presence of flavonoids, steroids/terpenoids, and alkaloids, which represent the three groups of secondary metabolites. The antimicrobial test was carried out using the well diffusion method, as a control used 80 ppm of ampicillin. The results of the study indicated that T. decurrens contains flavonoids, steroids, and alkaloids, G. rugosa contains flavonoids, terpenoids, and alkaloids, whereas H. opuntia only contains terpenoids and alkaloids. Furthermore, G. rugosa was found to have the best ability to inhibit bacteria, with an inhibition zone ranging from 2223 mm; in some treatments, the diameter of the inhibition zone was even larger than the positive control. T. decurrens was only effective in inhibiting the growth of S. aureus, whereas H. opuntia demonstrated the potential to inhibit the growth of S. aureus and E. coli, and for B. cereus and S. typhi, it could only be inhibited by 100% (1000 muL) extract of the H. opuntia extract.