Submerged Culture of Edible and Medicinal Mushroom Mycelia and Their Applications in Food Products: A Review.

Edible mushrooms have rich nutrition (e.g., proteins, dietary fibers, polysaccharides) and they can be potential sources of important ingredients in food processing. However, the cultivation of mushroom fruiting bodies needs a relatively long time, and they can be easily polluted during the growth process. At the same time, a lot of labor and larger planting areas are also required. As we all know, submerged fermentation is a good way to produce edible mushroom mycelia with less environmental pollution and small footprint, which are also rich in nutrition and bioactive components that are used as dietary supplements or health care products in the food industry. Therefore, it can be considered that the replacement of edible mushroom fruiting bodies with edible mushroom mycelia produced through submerged fermentation has great application potential in food production. At present, most of the research about edible mushroom mycelia focuses on the production of bioactive metabolites in fermentation liquid, but there are few reports that concentrate on their applications in food. This paper reviews the research progress of submerged culture of edible mushroom mycelia and their applications in food products.

Enhancement of carotenoid production and its regulation in edible mushroom Cordyceps militaris by abiotic stresses.

Cordyceps militaris carotenoids are widely used as food additives, animal feed supplements, and so on. However, the biosynthetic pathway of carotenoids in C. militaris is still obscure. In this paper, changes of mycelial morphology and carotenoid accumulation of C. militaris were investigated under oxidative (KMnO4) and osmotic stress (NaCl). Subsequently, qRT-PCR was employed to detect the expression levels of genes related to carotenogenesis to explore the mechanism of adaptation to abiotic stress. When the concentrations of KMnO4 and NaCl were respectively 0.4 g/L and 2 g/L, carotenoid accumulation reached a maximum of 6616.82 ±â€¯666.43 µg/g and 6416.77 ±â€¯537.02 µg/g. Under the oxidative stress condition of KMnO4, the expressions of psy and hsp70 increased significantly compared with control. Besides, the genes fus3 and hog1 were significantly enriched in the MAPK signal pathway. Compared with the control group, there was no significant difference in expression of psy in the NaCl group. Moreover, the accumulation of triacylglycerols may contribute significantly to the increase in carotenoid accumulation. The increased accumulation of antioxidant carotenoids induced under environmental stress is to resist oxidative conditions. Fus3 and Hog1 signaling in the MAPK pathway was activated and subsequently take effects on the resistance of oxidative condition by regulating related metabolic processes. C. militaris resist the stress of high oxygen by producing a large amount of glycerol and carotenoids when this fungus is cultured in a saline environment for a long time.

Structural Analysis and Antioxidant Activity of Extracellular Polysaccharides Extracted from Culinary-Medicinal White Jelly Mushroom Tremella fuciformis (Tremellomycetes) Conidium Cells.

Using Tremella fuciformis conidium cells for submerged fermentation is a cost-effective way to harvest bioactive compounds. In this study, we emphasized the structural and functional analysis of extracellular polysaccharides (EPS) extracted from T. fuciformis conidium cells. An EPS high-yield strain tyc63 was selected and a 6-day optimum fermentation period was determined. Crude EPS was extracted and three high molecular weight (5189, 171.6, and 661 kDa) polysaccharides TFP-1, TFP-2, and TFP-3 were isolated and purified. TFP-1 is mainly composed of glucose, xylose, mannose, and fucose, while both TFP-2 and TFP-3 are mainly composed of rhamnose, arabinose, mannose, galactose, and glucose. FT-IR analysis revealed that TFP-1, TFP-2, and TFP-3 have typical polysaccharide structure. The antioxidant assay revealed that the crude EPS, TFP-1, TFP-2, and TFP-3 presented high free radical scavenging activities but low ferric reducing power, suggesting that the EPS produced by liquid fermentation could be used as a potent radical scavenger.

The Biosynthetic Pathway of Ergothioneine in Culinary-Medicinal Winter Mushroom, Flammulina velutipes (Agaricomycetes).

Ergothioneine is a natural 2-thiol-amidazole amino acid that plays an important role in inflammation, depression, and cardiovascular disease. Flammulina velutipes is a common basidiomycete mushroom rich in ergothioneine (EGT). However, the biosynthetic pathway of EGT in F. velutipes is still unclear. In this study, the F. velutipes ergothioneine biosynthetic gene 1 (Fvegtl), F. velutipes ergothioneine biosynthetic gene 2 (Fvegt2), and F. velutipes ergothioneine biosynthetic gene 3 (Fvegt3) were cloned and expressed, and the activities of the proteins encoded by these three genes (FvEgt1, F. velutipes ergothioneine biosynthase 1; FvEgt2, F. velutipes ergothioneine biosynthase 2; and FvEgt3, F. velutipes ergothioneine biosynthase 3) were identified. The results showed that FvEgtl not only has the function of methyltransferase, but also has the function of hercynlcysteineteine sulfoxide (Hersul) synthase, which can catalyze the production of Hersul from histidine and cysteine in F. velutipes. FvEgt2 and FvEgt3 are two functionally different cysteine desulfurase enzymes. Among them, FvEgt2 is a cysteine-cysteine desulfurase-which catalyzes the activation of the S-H bond on cysteine, while FvEgt3 is a pyridoxal phosphate (PLP)-dependent cysteine desulfurase responsible for catalyzing the production of ketimine complex. Our results show that FvEgt1/FvEgt2/FvEgt3 can simultaneously catalyze the production of EGT by histidine, cysteine, and pyridoxal phosphate. Collectively, the in vitro synthesis of EGT in the edible fungus F. velutipes was first achieved, which laid the foundation for the biological production of EGT.

An Efficient Strategy for Enhancement of Bioactive Compounds in the Fruit Body of Caterpillar Medicinal Mushroom, Cordyceps militaris (Ascomycetes), by Spraying Biotic Elicitors.

Cordyceps militaris is a mushroom species with high nutritive and medicinal values based on diverse bioactive metabolites. The contents of bioactive ingredients are indicative of the quality of commercially available fruit body of this fungus. Although the application of biotic elicitors has been an efficient strategy to induce the accumulation of valuable bioactive compounds in vivo, related research in C. militaris is rarely reported. In this study, five biotic elicitors in different concentrations (0.05, 0.5, 1, and 2 mg/mL), including chitosan (CHT), 2,4-dichlorophenoxyacetic acid (2,4-D), methyl jasmonate (MeJA), gibberellic acid (GA), and triacontanol (TRIA), were first introduced to enhance the production of 10 kinds of major bioactive components in the fruit body of C. militaris. Results showed that the effect of biotic elicitors on bioactive compounds in the fruit body of C. militaris was elicitor-specific and concentration-dependent. Overall, 1 mg/L CHT was considered the most favorable for the production of 10 bioactive ingredients in C. militaris fruit body, which could increase the content of protein, polysaccharides, polyphenol, triterpenoids, flavonoids, cordyceps acid, cordycepin, and anthocyanins by 20.38-, 1.41-, 0.7-, 0.47-, 11.90-, 1.09-, 0.34-, and 2.64-fold, respectively, compared with the control. The results of this study would provide an efficient strategy for the production of a superior quality fruit body of and contribute to further elucidation of the effects of biotic elicitors on metabolite accumulation in C. militaris.

Transcriptome Analysis of Cordyceps militaris Reveals Genes Associated With Carotenoid Synthesis and Identification of the Function of the Cmtns Gene.

Cordyceps militaris, a valuable edible and medicinal fungus, has attracted increasing attention because of its various bioactive ingredients. However, the biosynthetic pathway of C. militaris carotenoids is still unknown due to lack of transcriptome information. To uncover genes related to the biosynthesis of C. militaris carotenoids, the transcriptomes of mycelia CM10_D cultured under dark conditions and mycelia CM10_L cultured under light exposure conditions were sequenced. Compared with mycelia CM10_D, 866 up-regulated genes and 856 down-regulated genes were found in mycelia CM10_L. Gene ontology (GO) analysis of differentially expressed genes (DEGs) indicated that DEGs were mainly classified into the "metabolic process," "membrane," and "catalytic activity" terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs suggested that DEGs were mainly enriched in "metabolic pathways," "MAPK signaling pathway-yeast," and "biosynthesis of secondary metabolites." In addition, the carotenoid content of the Cmtns gene deletion mutant (ΔCmtns) was significantly lower than that of the wild-type C. militaris CM10, while the carotenoid content of the complementary strain (ΔCmtns-c) of the Cmtns gene was not significantly different from that of C. militaris CM10, suggesting that the Cmtns gene significantly affected the biosynthesis of carotenoids in C. militaris. These results potentially pave the way for revealing the biosynthetic pathway of carotenoids and improving carotenoids production in C. militaris.

Optimization of Cultivation Conditions of Lingzhi or Reishi Medicinal Mushroom, Ganoderma lucidum (Agaricomycetes) for the Highest Antioxidant Activity and Antioxidant Content.

Ganoderma lucidum is a famous medicinal mushroom that is rich in antioxidants. The content of antioxidant components of grains can be effectively improved by G. lucidum as the fermenting strain. Optimization of the solid-state fermentation medium and optimization of the fermentation conditions were studied. The optimal fermentation substrate combination of G. lucidum TS (GL-TS) was 46.79% buckwheat, 53.21% rice; the optimal fermentation substrate combination of G. lucidum Am (GL-Am) was 4.17% soybean, 95.83% rice. The optimal fermentation conditions of GL-TS and GL-Am were as follows: inoculum amounts of 4.5% and 7.5%, temperatures of 30°C and 32°C, medium moisture content of 70% for both media, material granularities of 0.212-0.355 mm and 0.500-0.710 mm, and optimal fermentation time of 12.0 d and 10.5 d, respectively. Results of the analysis of antioxidant components in the fermentation substrates indicated that the antioxidant components were rich in antioxidant varieties and high in content. The contents of the antioxidant components (triterpenoids, total polyphenols, reducing sugars, anthocyanins, superoxide dismutase, glutathione, vitamin C, and vitamin E) in the full-fermentation substrates were greater than those in the nonfennentation substrates (except for flavonoids in the full-fermentation substrates, which were less than in the nonfennentation substrates). Glutathione was the major antioxidant component in the fermentation substrates, and the glutathione content was the highest. Therefore, the fermentation substrates of G. lucidum can be used to make antioxidant foods. This research contributes to the foundation for developing antioxidant foods based on G. lucidum.

Increasing of the Contain of Carotenoids in Caterpillar Mushroom, Cordyceps militaris (Ascomycetes) by Using the Fungal Elicitors Cultivation.

As a natural pigment, cordycepic carotenoids have many bioactive functions, such as antiinflammation, anticancer, and antioxidation. In addition, the good coloring of this hydrophilic pigment enables it to have wide application in the food industry. This study investigated five species of fungal elicitors, namely, Rhodotorula glutinis, Saccharomyces cerevisiae, Monascus ruber, Blakeslea trispora, and Flammulina velutipes, to evaluate their effects on carotenoid accumulation in Cordyceps militaris. Results showed that all fungal elicitors, except Rh. glutinis, have no positive effect on the biosynthesis of cordycepic carotenoids. The Rh. glutinis elicitor remarkably stimulated the accumulation of carotenoids with a 13.72% increase compared with the control. Subsequently, the entire Rh. glutinis elicitor (part NHK) was divided into three parts, namely, exopolysaccharide (EPS) (part E), mixture of EPS and protein (part PE), and other components (part O), to analyze their effects on carotenoid accumulations. Results showed that part O may be the effective component that remarkably stimulates the biosynthesis of carotenoids with a 26% increase compared with the control. This research demonstrated that Rh. glutinis elicitor can effectively increase the content of natural carotenoids in C. militaris, and provided an important reference for the development and utilization of carotenoid industrialization.

A novel process for obtaining pinosylvin using combinatorial bioengineering in Escherichia coli.

Pinosylvin as a bioactive stilbene is of great interest for food supplements and pharmaceuticals development. In comparison to conventional extraction of pinosylvin from plant sources, biosynthesis engineering of microbial cell factories is a sustainable and flexible alternative method. Current synthetic strategies often require expensive phenylpropanoic precursor and inducer, which are not available for large-scale fermentation process. In this study, three bioengineering strategies were described to the development of a simple and economical process for pinosylvin biosynthesis in Escherichia coli. Firstly, we evaluated different construct environments to give a highly efficient constitutive system for enzymes of pinosylvin pathway expression: 4-coumarate: coenzyme A ligase (4CL) and stilbene synthase (STS). Secondly, malonyl coenzyme A (malonyl-CoA) is a key precursor of pinosylvin bioproduction and at low level in E. coli cell. Thus clustered regularly interspaced short palindromic repeats interference (CRISPRi) was explored to inactivate malonyl-CoA consumption pathway to increase its availability. The resulting pinosylvin content in engineered E. coli was obtained a 1.9-fold increase depending on the repression of fabD (encoding malonyl-CoA-ACP transacylase) gene. Eventually, a phenylalanine over-producing E. coli consisting phenylalanine ammonia lyase was introduced to produce the precursor of pinosylvin, trans-cinnamic acid, the crude extraction of cultural medium was used as supplementation for pinosylvin bioproduction. Using these combinatorial processes, 47.49 mg/L pinosylvin was produced from glycerol.