Antioxidant activity and metabolite profiling of the soft coral Sinularia sp. from Sabah, Malaysia, using FTIR, GC-MS, and LC-orbitrap-MS/MS

Aim: This study aims to evaluate the antioxidant activities and profile the bioactive compounds of Sinularia sp. collected from the waters of Sabah, Malaysia. Methods: Total phenolic and flavonoid contents, as well as the antioxidant activity [2,2-diphenyl-1-picrylhydrazyl (DPPH); 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)] of Sinularia sp. methanol extract were evaluated. Additionally, profiling of bioactive compounds was performed using Fourier transform infrared spectroscopy (FTIR), gas chromatography and mass spectrometry (GC-MS), and liquid chromatography-orbitrap-tandem mass spectrometry (LC-orbitrap-MS/MS) approaches. Results: Sinularia sp. methanol extract contained total phenolic content of 0.053 ± 0.001 mg gallic acid equivalent (GAE)/g and total flavonoid content of 1.78 ± 0.034 mg quercetin equivalents (QE)/g. The antioxidant activities determined by DPPH and ABTS assays showed half-maximal inhibitory concentration (IC50) values of 6.23 ± 0.17 mg/mL and 3.28 ± 0.07 mg/mL, respectively, while the standard ascorbic acid exhibited the highest activity with IC50 values of 0.15 ± 0.01 and 0.08 ± 0.01 mg/mL, respectively. FTIR analysis confirmed functional groups indicative of bioactive compounds, while GC-MS and LC-orbitrap-MS/MS identified 13 and 59 detections, respectively, containing fatty acids, fatty acid esters, alkaloids, steroids, and marine sterols. Interestingly, the key identified antioxidant compounds include vitamin E, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA). Conclusions: In conclusion, Sinularia sp. exhibits promising antioxidant potential. Further studies are required to isolate and characterize active compounds for therapeutic applications.