Extraction, physicochemical properties, and antioxidant activity of natural melanin from Auricularia heimuer fermentation

Abstract

IntroductionNatural melanin from Auricularia heimuer have numerous beneficial biological properties, which were used as a safe and healthy colorant in several industries.MethodsIn this study, single-factor experiments, Box-Behnken design (BBD), and response surface methodology (RSM) were employed to investigate the effects of alkali-soluble pH, acid precipitation pH, and microwave time on the extraction yield of Auricularia heimuer melanin (AHM) from fermentation. Ultraviolet-visible spectrum (UV-Vis), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and high-performance liquid chromatography (HPLC) were used to analyze the extracted AHM. The solubility, stability, and antioxidant activities of AHM were also measured.ResultsThe results showed that alkali-soluble pH, acid precipitation pH, and microwave time significantly affected the AHM yield, with the following optimized microwave-assisted extraction conditions: alkali-soluble pH of 12.3, acid precipitation pH of 3.1, and microwave time of 53 min, resulting in an AHM extraction yield of 0.4042%. AHM exhibited a strong absorption at 210 nm, similar to melanin from other sources. FT-IR spectroscopy also revealed that AHM exhibited the three characteristic absorption peaks of natural melanin. The HPLC chromatogram profile of AHM showed a single symmetrical elution peak with a 2.435 min retention time. AHM was highly soluble in alkali solution, insoluble in distilled water and organic solvents, and demonstrated strong DPPH, OH, and ABTS free radical scavenging activities.DiscussionThis study provides technical support to optimize AHM extraction for use in the medical and food industries.

Synthesis and structural characteristics analysis of melanin pigments induced by blue light in Morchella sextelata

“…The maximum absorption peak of the two melanin pigments in M. sextelata was observed at 220 nm in the UVvisible absorption spectrum. The results presented herein are consistent with the commonly observed UV-visible absorption characteristics of typical melanin, although they show slight deviations at the maximum absorption peak (Ma et al, 2023). These variations in maximum absorbance could be attributed to differences in the source of melanin, which may result in minor alterations to its natural structure.…”

“…M. sextelata melanin pigments also showed characteristic bands for aromatic rings and sulphur at 730 cm −1 and 678 cm −1 . Comparative results between M. sextelata melanin pigments and those found in other organisms such as A. heimuer (Ma et al, 2023), and oyster mushroom (Zhang et al, 2021), indicate a similarity in their characteristic peak absorption spectra obtained through FTIR analysis. This similarity further supports the notion that there might be commonalities in terms of melanin composition among different species.…”

“…The melanin pigments of M. sextelata were analyzed using the HPLC method and compared with standard eumelanin (M8631, Sigma-Aldrich, St. Louis, MO, United States) (Ma et al, 2023). The pigments and the standard eumelanin were dissolved in a 0.5 M NaOH solution at a final concentration of 50 mg/L.…”