Abstract
<title>Abstract</title> <p> Fucoxanthin is a naturally occurring carotenoid from brown seaweeds that has been known to be an antibacterial agent. Apart from its health benefits, the potential use of fucoxanthin as an antibacterial agent in aquaculture remains poorly understood. The present study primarily focused on the quantitative and functional characterization of fucoxanthin derived from <italic>Sargassum ilicifolium</italic> , with a specific emphasis on identifying hydroxyl (-OH) functional groups and their contribution to its antibacterial efficacy against <italic>Vibrio parahaemolyticus</italic> , the principal pathogen affecting whiteleg shrimp ( <italic>Litopenaeus vannamei</italic> ). Ethanol, methanol, ethyl acetate, and water were used individually as solvents for purification and screening. LC-MS profiling was employed for qualitative component identification; HPLC was used to measure purity; FTIR spectroscopy was applied to determine functional groups. The maximum concentration of fucoxanthin (3.112 ± 0.0610 ppm) was detected in fresh Sargassum extracted with ethanol, whereas dried <italic>Sargassum</italic> (simplisia) extracted with ethyl acetate yielded 0.93 ppm. Both extracts exhibited a robust and sustained presence of hydroxyl groups and demonstrated the most significant antibacterial efficacy against <italic>V. parahaemolyticus</italic> . The molecular characteristics of fucoxanthin unequivocally indicate its antibacterial efficacy, and there is compelling evidence that the hydroxyl group plays a role in the inhibitory mechanism against <italic>V. parahaemolyticus</italic> . The most effective lethal bactericidal concentrations were 100 g/disk. These latest results establish a scientific basis for using fucoxanthin as a natural, bioactive, marine-sourced agent to control pathogens in shrimp aquaculture. </p>