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

Introduction: Natural melanin from Auricularia heimuer have numerous beneficial biological properties, which were used as a safe and healthy colorant in several industries. Methods: In 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. Results: The 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. Discussion: This study provides technical support to optimize AHM extraction for use in the medical and food industries.

Research progress of Auricularia heimuer on cultivation physiology and molecular biology.

Auricularia heimuer (A. heimuer F. Wu, B. K. Cui, Y. C. Dai), a well-known gelatinous fungus used for both food and medicine, is a major edible fungus with a more than 1000-year history of cultivation in China. The nutrients of A. heimuer are abundant, including polysaccharides, melanin, mineral elements, etc. The A. heimuer polysaccharides exhibit antioxidant, immunomodulatory, and anticancer properties. A. heimuer is a completely different species grown in China, unlike Auricularia auricula-judae (Bull.) Quel, which was used to characterize it. The cultivated strain varies based on the local climatic factors and cultivation practices. Hardwood chips are the primary material utilized in the cultivation of substitute materials, which is the principal cultivation technique. However, in actual production, straw is frequently replaced for some wood chips to address the issue of a lack of wood. There are three different types of growing techniques: open-air ground cultivation, arch cultivation, and shed-type hanging substitute cultivation of these three, the quality of A. heimuer grown in a shed is superior to that grown in an open-air environment. The A. heimuer genome sequencing project started later than expected, and the entire genome sequencing was not finished until 2019. A. heimuer's molecular biology studies have mostly concentrated on analyzing genetic diversity and identifying cultivars using molecular markers including RAPD, ISSR, and ITS. There have only been a small number of studies on the function of A. heimuer genes, which have only focused on the preliminary cloning and expression study of a few genes, including the laccase gene and the triterpene compound production gene, among others. However, there is still a lack of comprehensive information concerning A. heimuer, necessitating a synopsis. To our knowledge, this is the first published review of A. heimuer, and it summarizes the most recent studies on its molecular biology and cultivation. This review can serve as a guide for future research on the fungus.

Optimization of Melanin Extraction from the Wood Ear Medicinal Mushroom, Auricularia auricula-judae (Agaricomycetes), by Response Surface Methodology and Its Antioxidant Activities In Vitro.

The optimal conditions for melanin extraction from Auricularia auricula-judae (Hei 29) fruiting bodies was determined on the basis of the extract yield of melanin, calculated by using a single-factor experiment and response surface methodology. Its antioxidant activities were also studied in vitro. Various optimal process conditions for melanin extraction were determined by using Design-Expert software: incubation temperature, 69.11°C; incubation time, 58.66 minutes; and incubation pH, 12.81. Under these conditions, the melanin yield was 2.59%. We found that the antioxidant activities of A. auricula-judae melanin in vitro were strong against DPPH radicals and superoxide anions. The rate of DPPH radical scavenging was 63.04% when the A. auricula-judae melanin concentration was 0.36 mg/mL; the rate of superoxide anion scavenging reached 39.79% when the concentration was 0.375 mg/mL. However, the antioxidant activity against hydroxyl radicals was somewhat weak; the rate of scavenging reached only 7.47% when the A. auricula-judae melanin concentration was 0.06 mg/mL.

Identification of a New Fungal Pathogen Causing White Villous Disease on the Fruiting Body of the Culinary-Medicinal Mushroom Auricularia auricula-judae (Agaricomycetes) in China.

Auricularia auricula-judae is an edible and medicinal fungus ranking fourth in production among the edible fungi cultivated worldwide. White villous disease is rampant in Northeast China; it infects the fruiting bodies of A. auricula-judae by forming a white mycelial layer on its ventral side. The disease not only causes an unacceptable morphological appearance and a poor-quality product, but it also significantly reduces the yield. In this study, based on fungal morphology, ribosomal DNA internal transcribed spacer sequences, identification of species-specific primers, and the pathogenicity of the mycelia and spores, 2 fungal pathogens were isolated and identified as Fusarium equiseti and F. sporotrichioides.

High-Yield Production in Escherichia coli of Fungal Immunomodulatory Protein Isolated from Flammulina velutipes and Its Bioactivity Assay in Vivo.

A fungal immunomodulatory protein isolated from Flammulina velutipes (FIP-fve) has structural similarity to the variable region of the immunoglobulin heavy chain. In the present study, the recombinant bioactive FIP-fve protein with a His-tag in N-terminal of recombinant protein was expressed in transetta (DE3) at a high level under the optimized culturing conditions of 0.2 mM IPTG and 28 °C. The efficiency of the purification was improved with additional ultrasonication to the process of lysozyme lysis. The yield of the bioactive FIP-fve protein with 97.1% purity reached 29.1 mg/L with a large quantity for industrial applications. Enzyme-linked immunosorbent assay showed a maximum increase in interleukin-2 (IL-2) and gamma interferon (IFN-γ) for the mice serum group of 5 mg/kg body mass (p < 0.01) with three doses of His-FIP-fve. However, the production of IL-4 had no apparent difference compared to the control.