Marine macroalgae, particularly Padina australis, are recognized as promising sources of bioactive compounds with antibacterial potential. Ensuring the consistency and quality of such natural extracts is essential for their reliable use in pharmaceutical and biotechnological applications. This study aimed to evaluate the quality of Padina australis extract prepared with 96% ethanol using infrared (IR) spectroscopy as a rapid and non-destructive analytical method. The research was conducted to identify the characteristic functional groups present in the extract and to assess their relevance to antibacterial activity.

The extraction process utilized maceration with 96% ethanol as solvent, followed by concentration under reduced pressure to obtain a crude extract. The chemical profile of the extract was analyzed using Fourier Transform Infrared (FTIR) spectroscopy within the wavelength range of 4000–400 cm⁻¹. The obtained spectra revealed absorption bands corresponding to functional groups such as O–H (hydroxyl), C=O (carbonyl), and C–O (ether and ester), indicating the presence of phenolic, flavonoid, and fatty acid compounds known for antibacterial properties.