Lentinan degradation in the Lentinula edodes fruiting body during postharvest preservation is reduced by downregulation of the exo-β-1,3-glucanase EXG2

Recent Advances in the Application of Natural Products for Postharvest Edible Mushroom Quality Preservation

Edible mushrooms are favored by consumers for their excellent nutritional value and pharmacological properties. However, fresh mushrooms are highly perishable and undergo rapid quality deterioration induced by a series of intrinsic and extrinsic factors during postharvest storage. In recent years, the application of natural products derived from plants, animals, microorganisms, and other sources in mushroom quality preservation has drawn increasing attention. Compared to chemical preservatives, natural products show similar or higher biological activity and have few side effects on human health. This review summarizes the recent advances in the application of natural products used for quality maintenance of postharvest mushrooms. These natural substances mainly include essential oils, polyphenols, polysaccharides, bacteriocins, and other extracts. They have the potential to inhibit mushroom weight loss, softening, and browning, reduce the count of pathogenic microorganisms, and retain nutrients and flavor, effectively improving the quality of mushrooms and extending their shelf-life. The preservation techniques for natural products and their preservation mechanisms are also discussed here. Overall, this review provides current knowledge about natural products in edible mushroom preservation and aims to inspire more in-depth theoretical research and promote further practical application.

Extracellular enzymes secreted in the mycelial block of Lentinula edodes during hyphal growth

Lentinula edodes (shiitake mushroom) is one of the most widely cultivated edible mushrooms and is primarily cultivated using sawdust medium. While there have been improvements in the cultivation technology, the mechanism of mycelial block cultivation, such as mycelial growth and enzymatic sawdust degradation, has not been clarified. In this study, the mycelium was elongated longitudinally in the bottle sawdust culture for 27 days, and the cultivated sawdust medium was divided into three sections (top, middle, and bottom parts). To determine spatial heterogeneity in the enzyme secretion, the enzymatic activities of each part were analyzed. Lignocellulose degradation enzymes, such as endoglucanase, xylanase, and manganese peroxidase were highly secreted in the top part of the medium. On the other hand, amylase, pectinase, fungal cell wall degradation enzyme (β-1,3-glucanase, β-1,6-glucanase, and chitinase), and laccase activities were higher in the bottom part. The results indicate that the principal sawdust degradation occurs after mycelial colonization. Proteins with the laccase activity were purified from the bottom part of the medium, and three laccases, Lcc5, Lcc6 and Lcc13, were identified. In particular, the expression of Lcc13 gene was higher in the bottom part compared with the level in the top part, suggesting Lcc13 is mainly produced from the tip region and have important roles for mycelial spread and nutrient uptake during early stage of cultivation.

Lentinan confers protection against type 1 diabetes by inducing regulatory T cell in spontaneous non-obese diabetic mice

BACKGROUND

Lentinan (LNT) is a complex fungal component that possesses effective antitumor and immunostimulating properties. However, there is a paucity of studies regarding the effects and mechanisms of LNT on type 1 diabetes.

OBJECTIVE

In the current study, we investigated whether an intraperitoneal injection of LNT can diminish the risk of developing type 1 diabetes (T1D) in non-obese diabetic (NOD) mice and further examined possible mechanisms of LNT's effects.

METHODS

Pre-diabetic female NOD mice 8 weeks of age, NOD mice with 140-160 mg/dL, 200-230 mg/dL or 350-450 mg/dL blood glucose levels were randomly divided into two groups and intraperitoneally injected with 5 mg/kg LNT or PBS every other day. Then, blood sugar levels, pancreas slices, spleen, PnLN and pancreas cells from treatment mice were examined.

RESULTS

Our results demonstrated that low-dosage injections (5 mg/kg) of LNT significantly suppressed immunopathology in mice with autoimmune diabetes but increased the Foxp3+ regulatory T cells (Treg cells) proportion in mice. LNT treatment induced the production of Tregs in the spleen and PnLN cells of NOD mice in vitro. Furthermore, the adoptive transfer of Treg cells extracted from LNT-treated NOD mice confirmed that LNT induced Treg function in vivo and revealed an enhanced suppressive capacity as compared to the Tregs isolated from the control group.

CONCLUSION

LNT was capable of stimulating the production of Treg cells from naive CD4 + T cells, which implies that LNT exhibits therapeutic values as a tolerogenic adjuvant and may be used to reverse hyperglycaemia in the early and late stages of T1D.

Characterization of an active film prepared with Lentinus edodes (shiitake) polysaccharide and its effect on post-harvest quality and storage of shiitake

The aim of this study was to prepare a film based on shiitake (Lentinus edodes) stalk polysaccharides (LEP) for mushroom preservation. The effects of different LEP concentrations on physical, mechanical, antioxidant, and antimicrobial properties of the prepared film were evaluated. Using scanning electron microscopy, it was revealed that the addition of 1.5 % LEP resulted in homogeneous distribution in the prepared film, as well as greatly improved its antimicrobial properties. Moreover, LEP film resulted in superior mushroom preservation by regulating enzyme activities related to mushroom browning and softening, thereby decaying these processes. In addition, the prepared film maintained mushroom quality by reducing the accumulation of H₂O₂ and activating the regulatory system against oxidative stress. Collectively, the findings of the present study highlight the potential benefits of LEP films as a strategy to improve mushroom quality and prevent post-harvest spoilage, hence constituting a novel prospect for the development of shiitake by-products.

Effect of shiitake mushrooms polysaccharide and chitosan coating on softening and browning of shiitake mushrooms (Lentinus edodes) during postharvest storage

We investigated the browning and softening of fresh Lentinula edodes (LE) coated with polysaccharides (LEP) isolated from LE stalks and stored at 4 °C for 15 days. The results showed that compared to the chitosan-coated and uncoated LE, the LEP-treated mushrooms showed significant improvements in several qualities during storage, such as reduced weight loss, retention of hardness and springiness, improved soluble protein content, and reduced browning, malondialdehyde content, and electrolyte leakage rate. The best results were obtained with 1.5 % LEP. LEP improved the activities of peroxidase, catalase, superoxide dismutase, ascorbate peroxidase, and phenylalanine ammonialyase and significantly reduced the accumulation of hydrogen peroxide during storage compared to the control samples. In addition, the LEP treatment maintained the high antioxidant activity of LE during storage. Notably, LEP inhibited browning-related enzymes (polyphenol oxidase and tyrosinase) to reduce browning. It also maintained high levels of cellulase, chitinase, and β-1,3 glucanase to improve softening during storage. These findings suggest the potential of LEP to improve the post-harvest quality of mushrooms, allowing a storage period of up to 15 days (extending the shelf life by six days) and indirectly suggesting that the polysaccharide component of LEP can act as a self-defense additive to protect against spoilage during storage.

Lentinan extends lifespan and increases oxidative stress resistance through DAF-16 and SKN-1 pathways in Caenorhabditis elegans

Lentinan, extracted from Lentinus edodes, exhibits bioactive properties in vitro; however, little is known about the antioxidant potential in vivo. In this study, the effects of lentinan at 0.05, 0.25 and 1.25 mg/mL on the lifespan, locomotion, reproductive capacity, and oxidative stress resistance in Caenorhabditis elegans were determined. Compared to the untreated control, lentinan at 0.05, 0.25 and 1.25 mg/mL significantly prolonged the lifespan by 17.6%, 35.3% and 25.3% (p < 0.001), respectively, and improved the brood size, locomotion and stress resistance of the nematodes. Furthermore, lentinan at 0.25 mg/mL significantly reduced accumulation of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) by 38.1% (p = 0.013) and 49.7% (p = 0.028), respectively. In addition, lentinan at all tested concentrations significantly increased the activities of superoxide dismutase (SOD) and catalase (CAT). The expression of skn-1 and daf-16 in the treatments with lentinan at 0.25 and 1.25 mg/mL was significantly (p < 0.005) up-regulated compared with the untreated control, whereas that of the daf-2 gene was significantly down-regulated. Further evidence revealed that ROS production in lentinan-treated daf-16 and skn-1 mutant strains was similar to the untreated control. Consistent with the aforementioned results, lentinan enhanced the nuclear translocation of DAF-16 and SKN-1. Our results demonstrated that lentinan could increase lifespan and protect the nematodes from oxidative stress through DAF-16 and SKN-1.

Overexpressing Pleurotus ostreatus rho1b results in transcriptional upregulation of the putative cellulolytic enzyme-encoding genes observed in ccl1 disruptants

The transcriptional expression pattern of lignocellulolytic enzyme-encoding genes in white-rot fungi differs depending on the culture conditions. Recently, it was shown that 13 putative cellulolytic enzyme-encoding genes were significantly upregulated in most Pleurotus ostreatus ligninolysis-deficient mutant strains on beech wood sawdust medium. However, the mechanisms by which this transcriptional shift is triggered remain unknown. In this study, we identified one mechanism. Our previous study implied that histone H3 N-dimethylation at lysine 4 level possibly affects the shift; therefore, we analysed the expression pattern in the disruptants of P. ostreatus ccl1, which encodes a putative component of the COMPASS complex mediating the methylation. The results showed upregulation of 5 of the 13 cellulolytic enzyme-encoding genes. We also found that rho1b, encoding a putative GTPase regulating signal transduction pathways, was upregulated in the ccl1 disruptants and ligninolysis-deficient strains. Upregulation of at least three of the five cellulolytic enzyme-encoding genes was observed in rho1b-overexpressing strains but not in ccl1/rho1b double-gene disruptants, during the 20-day culture period. These results suggest that Rho1b may be involved in the upregulation of cellulolytic enzyme-encoding genes observed in the ccl1 disruptants. Furthermore, we suggest that Mpk1b, a putative Agaricomycetes-specific mitogen-activated protein kinase, functions downstream of Rho1b.

Intensive pulsed light pretreatment combined with controlled temperature and humidity for convection drying to reduce browning and improve quality of dried shiitake mushrooms

BACKGROUND

The change of surface color caused by browning during the drying process of shiitake mushrooms seriously affects its market circulation. Intensive pulsed light (IPL) as a non-heat-treatment method can reduce enzyme activity by changing the enzyme structure. Therefore, in this study, the use of IPL pretreatment before drying was aimed to reduce the adverse reactions caused by the browning reaction during the drying processing of shiitake mushrooms.

RESULTS

Shiitake mushrooms pretreated with 25 pulses of IPL energy of 400 J reduced the initial polyphenol oxidase enzyme activity, the browning index, and browning degree values by 42.83%, 43.02%, and 47.54% respectively. The IPL pretreatment enhanced the polysaccharides and reducing sugars contents and it reduced 5-hydroxymethylfurfural generation in the dried shiitake mushrooms. The pretreatment also improved the surface color, the antioxidant activity, and retained the umami taste characteristics in the dried shiitake mushroom.

CONCLUSION

The IPL pretreatment combined with controlled temperature and humidity for convection drying could be a suitable method to improve the quality of dried shiitake mushrooms. Therefore, this study provides a new pretreatment method for materials that are prone to browning during drying. © 2021 Society of Chemical Industry.

Molecular identification of Shiitake [Lentinula edodes Berk (Pegler)] and production of secondary metabolites with biotechnological potential

The Shitake mushroom (Lentinula edodes) is the second most-consumed mushroom in the world; in Colombia, it is cultivated and commercialized on a small scale in some supermarkets. Little is known about the precedence, nutritional and medicinal properties of Shiitake produced in Colombia. In this study, four shiitake isolates were grown in Colombia (LEUCO1, LEUCO2, LEUCO3, and LEUCO4) were sequenced in their ITS genes and evaluated for the production of three medicinal metabolites, eritadenine, ergotioneine and β-glucans (1,3-1, 6), using submerged culture. Genetic analysis revealed that all the isolates were close and related to the Japanese strain Cr62. LEUCO1 and LEUCO2 showed a distance of 0.000, as well as LEUCO3 and LEUCO4. All four isolates produced erythadenin in a range of 26.3-8.6 mg / L, with the best performance of LEUCO1 at 26.3 mg / L (p <0.05). Ergotioneine was produced with similar statistical yields in all the isolates with an average of 0.7 mg / g of dry weight biomass (DW). Β-glucans (1.3-1.6) were produced with yields of 5.6 - 3.8% of DW biomass, with the best values ​​for LEUCO2 and the lowest for LEUCO4 (p <0.05). In conclusion, we identified low genetic diversity in the four isolates, corresponding to two haplotypes with minimal genetic difference between them, related to the Japanese strain Cr62, indicating that Colombian farmers cultivate almost the same strains of shitake. Secondary metabolites, eritadenine, β-glucans and ergotioneine were found in promising yields useful for the pharmaceutical and food industries. More studies should be conducted to improve the yield of shitake metabolites through new growing conditions for industrial production and to find metabolic pathways and related genes.

Untargeted Metabolite Profiling of Antimicrobial Compounds in the Brown Film of Lentinula edodes Mycelium via LC-MS/MS Analysis

The brown film (BF) of Lentinula edodes mycelium has been reported to exert biological activities during mushroom cultivation; however, to date, there is limited information on its chemical composition. In this study, untargeted metabolomics analysis was performed via liquid chromatography-mass spectrometry (LC-MS), and the results were used to screen the antimicrobial compounds. A total of 236 differential metabolites were found among the BF stages compared with the white hyphal stage. Among them, five important antimicrobial metabolites related to antimicrobial activities, namely, 6-deoxyerythronolide B, tanikolide, hydroxyanthraquinone, benzylideneacetone, and 9-OxooTrE, were present at high levels in the BF samples. The score plots of the principal component analysis indicated that the samples from four time points could be classified into two groups. This study provided a comprehensive profile of the antimicrobial compounds produced during BF formation and partly clarified the antibacterial and antifungal mechanism of the BF of L. edodes mycelium.

Use of Lentinan To Control Sharp Eyespot of Wheat, and the Mechanism Involved

Lentinan (LNT), a complex polysaccharide with a β-(1→3)-linked backbone of d-glucose residues, has been reported to inhibit plant diseases. Our objective was to explore the efficacy and action mechanism of LNT used as a seed dressing to control sharp eyespot of wheat. Seed dressing promoted wheat growth. At control germination rates of 50%, 8 g of LNT/100 kg of seeds of the Jimai 22, Shannong 23, and Luyuan 502 cultivars significantly increased seed germination to 54%, 52%, and 51%, respectively. Seven days after emergence, the heights and root activity of wheat treated with LNT were significantly greater than those of controls. These effects were dose-dependent. At this time, the plant heights of Jimai 22, Shannong 23, and Luyuan 502 cultivars were 9.52, 8.52, and 10.52 cm, respectively, significantly higher than that of the controls. LNT prevented the development of wheat sharp eyespot. In the highly susceptible Jimai 22 cultivar, sharp eyespot development was reduced by 33.7%, 31.9%, and 30.4% at 7, 14, and 21 days after germination. LNT somewhat increased phenylalanine ammonia-lyase, peroxidase, and superoxide dismutase activity; reduced the malondialdehyde content; increased chlorophyll a and b levels; and enhanced the root vigor of wheat. These effects peaked 7 days after germination. LNT increased transcription of the genes encoding alternative oxidase (AOX) and β-1,3-glucanase (GLU), the salicylic acid signaling pathway-related gene NbPR1a, and the sharp eyespot resistance-related gene RS33. A significant dose-effect relationship was evident in terms of AOX transcription; we thus speculate that AOX may be the target gene.

Lentinula edodes Genome Survey and Postharvest Transcriptome Analysis

Lentinula edodes is a popular, cultivated edible and medicinal mushroom. Lentinula edodes is susceptible to postharvest problems, such as gill browning, fruiting body softening, and lentinan degradation. We constructed a de novo assembly draft genome sequence and performed gene prediction for Lentinula edodesDe novo assembly was carried out using short reads from paired-end and mate-paired libraries and by using long reads by PacBio, resulting in a contig number of 1,951 and an N₅₀ of 1 Mb. Furthermore, we predicted genes by Augustus using transcriptome sequencing (RNA-seq) data from the whole life cycle of Lentinula edodes, resulting in 12,959 predicted genes. This analysis revealed that Lentinula edodes lacks lignin peroxidase. To reveal genes involved in the loss of quality of Lentinula edodes postharvest fruiting bodies, transcriptome analysis was carried out using serial analysis of gene expression (SuperSAGE). This analysis revealed that many cell wall-related enzymes are upregulated after harvest, such as β-1,3-1,6-glucan-degrading enzymes in glycoside hydrolase (GH) families GH5, GH16, GH30, GH55, and GH128, and thaumatin-like proteins. In addition, we found that several chitin-related genes are upregulated, such as putative chitinases in GH family 18, exochitinases in GH20, and a putative chitosanase in GH family 75. The results suggest that cell wall-degrading enzymes synergistically cooperate for rapid fruiting body autolysis. Many putative transcription factor genes were upregulated postharvest, such as genes containing high-mobility-group (HMG) domains and zinc finger domains. Several cell death-related proteins were also upregulated postharvest.IMPORTANCE Our data collectively suggest that there is a rapid fruiting body autolysis system in Lentinula edodes The genes for the loss of postharvest quality newly found in this research will be targets for the future breeding of strains that keep fresh longer than present strains. De novoLentinula edodes genome assembly data will be used for the construction of a complete Lentinula edodes chromosome map for future breeding.

Are mushrooms medicinal?

Despite the longstanding use of dried mushrooms and mushroom extracts in traditional Chinese medicine, there is no scientific evidence to support the effectiveness of these preparations in the treatment of human disease. Consumers should evaluate assertions made by companies about the miraculous properties of medicinal mushrooms very critically. The potential harm caused by these natural products is another important consideration. In a more positive vein, the presence of potent toxins and neurotropic compounds in basidiomycete fruit bodies suggests that secondary metabolites with useful pharmacological properties are widespread in these fungi. Major investment in controlled experiments and objective clinical trials is necessary to develop this natural pharmacopeia.

Comparative Study of Nonautolytic Mutant and Wild-Type Strains of Coprinopsis cinerea Supports an Important Role of Glucanases in Fruiting Body Autolysis

Autolysis of Coprinopsis cinerea fruiting bodies affects its commercial value. In this study, a mutant of C. cinerea that exhibits pileus expansion without pileus autolysis was obtained using ultraviolet mutagenesis. This suggests that pileus expansion and pileus autolysis involve different enzymes or proteins. Among the detected hydrolytic enzymes, only β-1,3-glucanase activity increased with expansion and autolysis of pilei in the wild-type strain, but the increase was abolished in the mutant. This suggests that β-1,3-glucanases plays a major role in the autolysis. Although there are 43 possible β-1,3-glucoside hydrolases genes, only 4 known genes, which have products that are thought to act synergistically to degrade the β-1,3-glucan backbone of cell walls during fruiting body autolysis, and an unreported gene were upregulated during pileus expansion and autolysis in the wild-type stain but were suppressed in the mutant. This suggests that expression of these β-1,3-glucanases is potentially controlled by a single regulatory mechanism.