Effects of the drying method and extraction solvent on antioxidant and anti-inflammatory activity of Melosira nummuloides bioproducts

Melosira nummuloides is a marine diatom with potential use as food, fuel, and a dietary supplement. However, the efficacy of its extraction and drying techniques have not been explored. Here, M. nummuloides powders were prepared by two drying methods-hot-air drying (HAD) and freeze-drying (FD)-and extracted with hot water, ethanol, methanol, and chloroform:methanol (CM) at a ratio of 2:1 v/v. The antioxidant and anti-inflammatory activity of each extract was investigated. The CM extract had the greatest 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity among the solvent extracts, and a slight difference in antioxidant activity was observed across the various drying methods. Compared to other extracts, both the FD-CM and HAD-CM extracts showed stronger anti-inflammatory effects by inhibiting nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 cells. Furthermore, the FD-CM extract contained a wide range of lipophilic compounds. Notably, myristic acid (29.08 +/- 0.45 mg/g dry weight powder extract (DW)), oleic acid (25.20 +/- 0.92 mg/g DW), palmitoleic acid (10.77 +/- 0.41 mg/g DW), eicosapentaenoic acid (12.53 +/- 1.00 mg/g DW), neophytadiene (8.42 +/- 0.51 mg/g DW), and a-linolenic acid (1.27 +/- 0.005 mg/g DW) were among the prominent compounds identified. It is plausible to suggest that the abundance of these lipophilic compounds contributes to the remarkable antioxidative and anti-inflammatory potential exhibited by the FD-CM extract. Our results provide insights into the preferential drying methods and extraction solvents for producing M. nummuloides-based products with enhanced antioxidant and anti-inflammatory activity.