Acetylation of curcuminoids extract from Turmeric Rhizomes (Curcuma longa) as antibacterial compounds against S. aureus and E. coli

Abstract

Abstract Curcuminoid are active compounds of turmeric rhizome that widely known to have antibacterial activities. The low activity of curcuminoid as antimicrobial may be due to the presence of phenol moiety and hence it has low lipophilicity and low bioavailability. Antibacterial activities of curcuminoid derivatives may be improved by increasing their lipophilicity, one of which is replacing the hydrogen atom on the phenol groups with acetyl group by acetylation. The curcuminoids were extracted from turmeric rhizomes by Soxhlet method yielded of 10.24 %. This curcuminoids were structurally modified by acetylation using acetic anhydride with Ni/SiO2 catalyst. The products were separated through column chromatography then characterized using thin layer chromatography (TLC), UV-Vis, FTIR and LC-MS spectrometers. The results showed that the best condition of this reaction found when 15 % (w/w) catalyst was used with product conversion of 90.44 %. Diameter of inhibitory zone of acetyl curcuminoid derivatives showed the highest antibacterial activity at a concentration of 500 ppm against S. aureus of 18 mm and against E. coli of 13 mm. On the other hand, at the same concentration, the curcuminoid had inhibitory zone of 7.5 mm and 8 mm against S. aureus and E. coli, respectively. Therefore, the acetylation of curcuminoids has increased their antibacterial activities against Gram positive bacteria S. aureus up to 2.4 fold, while against Gram negative bacteria E. coli by only 1.6 fold.