Serial Extraction Technique of Rich Antibacterial Compounds in Sargassum cristaefolium Using Different Solvents and Testing their Activity

Background: S. cristaefolium is the brown seaweed extracted using the serial technique with different solvents. Methods: S. cristaefolium powder (50 mesh) was extracted with hexane, ethyl acetate, and methanol respectively. The S. cristaefolium powder residue had been dried before being re-extracted with the next different solvents. Three serial extracts were obtained and named as the 1-stage extract, 2-stage extract, and 3-stage extract. Besides, a single-step extract (extraction using only methanol) was also produced to compare with three serial extracts in antibacterial activity tests (against E. coli and S. aureus). The three serial extracts were detected their antibacterial compounds using GC-MS, LC-HRMS, and FT-IR. Results: The 3-stage extract had the highest extraction yield. On S. aureus, the inhibition zone in all extracts was not significantly different. On E.coli, the highest inhibition zone (5.42±0.14 mm) was the 3-stage extract, indeed it is higher than both antibiotic and a single-step extract. Phenol, 9-Tricosene(Z)-, palmitic acid, and oleamide were contained in all extracts. Other antibacterial compound types, both the 1-stage and 2-stage extracts contained 8 types whilst the 3-stage extract contained the most types (12 types). Particularly, hexyl cinnamic aldehyde and betaine were detected only in the 3-stage extract with the dominant area. The carboxylic acid groups were detected in all extracts to confirm the fatty acid structure. Several cinnamic aldehyde groups were detected only in the 3-stage extract. Conclusions: Thus, the extraction technique serially could produce the 3-stage extract which has the strongest antibacterial activity and the richest antibacterial compounds.