Determination of Antioxidant Activity, Phenolic Compounds, and Toxicity of Methanolic and Ethanolic Extracts of Pink Pigmented Facultative Methylotrophs (PPFM) Bacteria Pigment

Abstract

Pink-pigmented facultative methylotrophs bacteria are a plant’s surface inhabitant, especially at the leaf. They are known as Methylobacterium species. The antioxidant activity, phenolic compounds, and level of toxicity of this bacteria pigment have been studied. Recently, no previous research focused on the same bacterium found in Melicope lunu-ankenda (Gaertn.) T. G. Hartley, which is a component of the Malaysian ulam leaf. This study employed the 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric ion reducing antioxidant power (FRAP), and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays, along with total phenolic content determination to assess the antioxidant activities of the methanolic and ethanolic pigment extract. Additionally, the consumption safety level of the pigment extract used brine shrimp lethality assay. From these findings, ethanolic pigment extract has a higher antioxidant capacity than methanolic extract. The DPPH half-maximal inhibitory concentration (IC50) value of methanolic pigment extract is higher than ethanolic extract (0.72 ± 0.04 mg/ml), but the IC50 value is vice versa for ABTS (4.59 ± 2.17 mg/ml). Furthermore, ethanolic extracts have a high FRAP assay value (1.09 ± 0.19 mg/mg of trolox equivalent at 0.78 mg/ml sample) and phenolic content (1.39 ± 0.07 mg/mg of gallic acid equivalent at 0.78 mg/ml sample) compared to methanolic pigment extracts. Fortunately, the methanolic and ethanolic pigment extract’s lethal concentration values (4.52 and 9.94 mg/ml) are considered safe for food application since their toxicity level is higher than 1 mg/ml.