Postharvest biochemical characteristics and ultrastructure of Coprinus comatus

Transcriptome analysis reveals the effect of cold storage time on the expression of genes related to oxidative metabolism in Chinese black truffle

Chinese black truffle (Tuber indicum) is a hypogenous fungus of great value due to its distinctive aroma. In this study, both transcriptome and physicochemical analyses were performed to investigate the changes of nutrients and gene expression in truffle fruiting bodies during cold storage. The results of physicochemical analysis revealed the active metabolism of fruiting bodies in cold storage, showing the decreased contents of protein and soluble sugar, the variations in both polyphenol oxidase activity and total phenol content, and the detrimental effect of reactive oxygen species production caused by heavy metals (cadmium and lead) in truffles. Transcriptome analysis identified a total of 139,489 unigenes. Down-regulated expression of genes encoding the catalase-like domain-containing protein (katE), glutaredoxin protein (GRX), a copper/zinc superoxide dismutase (Sod_Cu), and aspartate aminotransferase (AAT) affected the degradation metabolism of intracellular oxides. Ribulose-5-phosphate-3-epimerase (RPE) was a key enzyme in response to oxidative stress in truffle cells through the pentose phosphate pathway (PPP). A total of 51,612 simple sequence repeats were identified, providing valuable resources for further genetic diversity analysis, molecular breeding, and genetic map-ping in T. indicum. Transcription factors GAL4 and SUF4-like protein were involved in glucose metabolism and histone methylation processes, respectively. Our study provided a fundamental characterization of the physicochemical and molecular variations in T. indicum during the cold storage at 4°C, providing strong experimental evidence to support the improvement of storage quality of T. indicum.

Long non-coding RNAs and their potential function in response to postharvest senescence of Sparassis latifolia during cold storage

Long non-coding RNAs (lncRNAs) have been shown to play crucial roles in response to aging processes. However, how lncRNAs regulate postharvest senescence of Sparassis latifolia (S. latifolia) with oriented polypropylene (OPP) film packing during cold storage remains unclear. In this study, we performed RNA-seq using the fruiting bodies of S. latifolia stored at 4 ℃ for 0, 8, 16 and 24 days after harvest, and profiled the lncRNA and mRNA transcriptome, respectively. In total, 1003 putative lncRNAs were identified, and there were 495, 483 and 162 differentially expressed (DE) lncRNAs, and 3680, 3941 and 1870 differentially expressed mRNAs after 8, 16 and 24 days of storage, respectively, compared to 0 day of storage. Target genes of differentially expressed lncRNAs were found to significantly associate with carbon and energy metabolism, response to abiotic stimulus, amino acid biosynthesis and metabolism, and protein synthesis and transcription. In addition, DE-lncRNA-mRNA co-expression networks in response to aging stress were also constructed. Taken together, these results confirm the regulatory role of lncRNAs in postharvest senescence of S. latifolia and will facilitate for improving preservation method.

Review of postharvest processing of edible wild-grown mushrooms

Edible wild-grown mushrooms, plentiful in resources, have excellent organoleptic properties, flavor, nutrition, and bioactive substances. However, fresh mushrooms, which have high water and enzymatic activity, are not protected by cuticles and are easily attacked by microorganisms. And wild-grown mushroom harvesting is seasonal the harvest of edible wild-grown mushrooms is subject to seasonality, so their market availability is challenging. Many processing methods have been used for postharvest mushroom processing, including sun drying, freezing, packaging, electron beam radiation, edible coating, ozone, and cooking, whose effects on the parameters and composition of the mushrooms are not entirely positive. This paper reviews the effect of processing methods on the quality of wild and some cultivated edible mushrooms. Drying and cooking, as thermal processes, reduce hardness, texture, and color browning, with the parallel that drying reduces the content of proteins, polysaccharides, and phenolics while cooking increases the chemical composition. Freezing, which allows mushrooms to retain better hardness, color, and higher chemical content, is a better processing method. Water washing and ozone help maintain color by inhibiting enzymatic browning. Edible coating facilitates the maintenance of hardness and total sugar content. Electrolytic water (EW) maintains total phenol levels and soluble protein content. Pulsed electric field and ultrasound (US) inhibit microbial growth. Frying maintains carbohydrates, lipids, phenolics, and proteins. And the mushrooms processed by these methods are safe. They are the focus of future research that combines different methods or develops new processing methods, molecular mechanisms of chemical composition changes, and exploring the application areas of wild mushrooms.

Postharvest quality and reactive oxygen species metabolism improvement of Coprinus comatus mushroom using allyl isothiocyanate fumigation

The aim of this study was to evaluate the effect of allyl isothiocyanate (AITC) on the reactive oxygen species (ROS) metabolism and quality of postharvest Coprinus comatus. Fresh mushrooms were stored at 4 °C with AITC at 5, 10 and 20 μL/L for 18 d, respectively. Sampling was performed every 3 d, and physicochemical parameters and ROS metabolism related enzymes activities were analyzed. Compared with that of control, the application of AITC at 10 μL/L significantly (P < 0.05) decreased xanthine oxidase activity after 9 d storage, while significantly (P < 0.05) improved the activities of succinic dehydrogenase, glutathione reductase, peroxidase, catalase and ascorbate peroxidase in the middle and later stage of storage. Furthermore, the Ca 2+-ATPase and superoxide dismutase activities in sample treated by 10 μL/L were all significantly (P < 0.05) higher than those in control. Therefore, the accumulation trends of malondialdehyde and ROS were retarded and membrane integrity was maintained. However, high concentration AITC (20 μL/L) treatment accelerated the ROS generation and increased electrolyte leakage rate. All AITC treatments significantly (P < 0.05) inhibited the respiration rate during the first 9 d storage and retarded browning of C. comatus during the storage of 18 d. These findings suggested that AITC treatment would be a promising method to maintain C. comatus quality but the concentration need to be optimized.

Transcriptome analysis of genes associated with autolysis of Coprinus comatus

Coprinus comatus, widely known as "Jituigu", is an important commodity and food in China. The yield of C. comatus, however, is substantially reduced by the autolysis of the fruiting bodies after harvest. To gain insight into the molecular mechanism underlying this autolysis, we divided the growth of C. comatus fruiting bodies into four stages: infant stage (I), mature stage (M), discolored stage (D), and autolysis stage (A). We then subjected these stages to de novo transcriptomic analysis using high-throughput Illumina sequencing. A total of 12,946 unigenes were annotated and analyzed with the Gene Ontology (GO), Clusters of Orthologous Groups of proteins (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG). We analyzed the differentially expressed genes (DEGs) between stages I and M, M and D, and D and A. Because the changes from M to D are thought to be related to autolysis, we focused on the DEGs between these two stages. We found that the pathways related to metabolic activity began to vary in the transition from M to D, including pathways named as autophagy-yeast, peroxisome, and starch and sucrose metabolism. This study also speculates the possible process of the autolysis of Coprinus comatus. In addition, 20 genes of interest were analyzed by quantitative real-time PCR to verify their expression profiles at the four developmental stages. This study, which is the first to describe the transcriptome of C. comatus, provides a foundation for future studies concerning the molecular basis of the autolysis of its fruiting bodies.

Proteomics Reveals the Mechanism Underlying the Autolysis of Postharvest Coprinus comatus Fruiting Bodies

Autolysis occurs widely in edible mushroom fruiting bodies after harvest, but the mechanism is still unclear. In this study, quantitative proteomics and bioinformatics analyses have been applied for revealing the autolysis mechanism of postharvest Coprinus comatus fruiting bodies. The results indicated that the autolysis mechanism of postharvest C. comatus was complicated. Before pileus opening, the carbohydrate metabolism including cell wall hydrolysis and energy biosynthesis, which were probably regulated by the ribosome, was involved in mushroom autolysis, whereas after pileus opening, the autolysis mechanism was related to the accumulated reactive oxygen species (ROS) and activated mitogen-activated protein kinase (MAPK) signaling pathway based on the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Furthermore, the changes in cell wall components and hydrolases, along with the production of ROS and the activities of oxidoreductase in C. comatus, were also verified to confirm the proteomic analysis results.

1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Plant Growth-Promoting Rhizobacteria Improve Drought Stress Tolerance in Grapevine (Vitis vinifera L.)

Plant growth-promoting rhizobacteria (PGPRs) that produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase are capable of reducing limits to plant growth due to water-deficient conditions. Here, seven PGPR strains that can produce ACC deaminase were successfully obtained from the rhizosphere soil of grapevine (Vitis vinifera L.) in arid regions of China. The strains belonged to three different genera: Pseudomonas, Enterobacter, and Achromobacter, according to their 16S rDNA sequencing analysis. A drought tolerance experiment revealed two PGPR strains (DR3 and DR6) with exceptionally high phosphate solubilization, nitrogen fixation, indoleacetic acid (IAA), and exopolysaccharides secretion potential. Both strains were selected for use in a pot experiment to evaluate their growth-promoting effects on grapevines under drought conditions. Each of these two PGPRs and their mixed inoculation into grapevines were expected to alleviate the comprehensive growth inhibition of grapevines caused by drought stress. The mixed inoculation was hypothesized to elicit the best growth-promoting effects. Inoculation with the PGPRs not only enhanced the root-adhering soil/root tissue ratios and soil aggregate stability, but it also increased the nitrogen and phosphorus levels in the soil and plant leaves. Further, inoculation with PGPRs significantly altered the plant height, biomass of shoot and root organs, relative water contents, and net photosynthetic rate of leaves, enabling grapevines to better cope with drought. Moreover, the contents of IAA, abscisic acid, and malondialdehyde in these grapevines under drought stress were significantly changed by PGPRs. They indirectly affected biochemical and physiological properties of grapevines to alleviate their drought stress. Taken together, these results demonstrate that the DR3 and DR6 PGPRs might be useful for effectively weakening the growth inhibition caused by drought in grapevines. The strains might also be applied as effective bioinoculants to maintain the quality of wine grapes.

Evaluation of Antioxidant Activities, Oxidation Enzymes, and Quality of Nano-Coated Button Mushrooms (Agaricus Bisporus) during Storage

Agaricus Bisporus is an edible button mushroom that is highly perishable with an extremely short shelf-life at ambient temperature. This work aims to evaluate some antioxidant activities, oxidation enzymes, and determine postharvest qualities of nano-coated mushrooms with the combination of chitosan (CHN) component during storage at 4 °C for (0, 3, 6, 9, and 12 days). Silica/CHN Film strongly delayed the mushroom respiratory spike onset and blocked carbon dioxide passage from inside to the outside, while Titanium/CHN Film (0.035 mmol s−1 kg−1) established the lowest O2 production rate and thiobarbituric acid reactive substances production (6.21 nmol g−1). Silica/CHN Film was mainly effectual for the polyphenol contents (0.39 g kg−1) and antioxidant activities (78.14% and 71.09%) for DPPH and ABTS+ radical scavenging activities, respectively. The results reported that Silica/CHN Film induced the highest (catalase and ascorbate peroxidase) activities, while Titanium/CHN Film recorded the highest (peroxidase and superoxide dismutase) activities of antioxidant enzymes. Besides, Titanium/CHN Film preserved relatively lower contents of hydrogen peroxide (22.40 µmol g−1) and hydroxyl radical (0.16 µmol g−1). In a word, nano-materials used in coating films such as titanium or even silica with the combination of CHN can directly reduce the cell degradation, oxidation processes and enhance the harvested horticultural crops.

Investigating the Nano-Films Effect on Physical, Mechanical Properties, Chemical Changes, and Microbial Load Contamination of White Button Mushrooms during Storage

Nutrient-rich edible white button mushrooms were coated with Chitosan (1%), Chitosan/nano-silica, and Chitosan/nano-titanium and then stored at 4 °C to investigate the physical, mechanical properties, chemical changes, and microbial load contamination at an interval of 3 days up to a 12 days storage period. It was noticed that Chitosan/nano-titanium and Chitosan/nano-silica preserved the weight loss percentages as 11.80% and 12.69%, respectively. Treatment with Chitosan/nano-silica coating was found to have positive impacts on the overall color parameters. Both of the nano-coating films enhanced headspace gas compositions and firmness. Chitosan/nano-silica samples recorded the least electrolyte leakage value (24.44%), as low oxygen gas concentration can reduce the respiration rate, weight loss, and cap opening. Chitosan/nano-titanium treatment showed the lowest cap opening value (19.58%), PPO activity (16.98 mg−1 protein), and microbial load contamination (6.12 log CFU/g) at the end of the whole storage period, suggesting that nano-films are a promising preservation method for prolonging the white button mushroom’s shelf-life.

Effect of Titanium Dioxide Nanocomposite Material and Antimicrobial Agents on Mushrooms Shelf-Life Preservation

Mushrooms have limited shelf-life and it can be prolonged if suitable conditions and treatments are effectively applied. In this study, nanocomposite material and antimicrobial agents with a combination of chitosan were used as novel packaging material for mushroom preservation. The microbiological analysis, physicochemical properties, headspace gas analysis, and polyphenol oxidase activity (PPO) during cold storage were investigated. As compared with control, coated mushrooms with chitosan (CHS), and nano-titanium dioxide CHSTiO2 thymol + tween-80 CHSTiO2/TT80 coating treatment showed significantly (p ≤ 0.05) lower respiration rate, microbial contaminations (4.27 log CFU/g), and (5.93 log CFU/g) for total yeast/mold and aerobic plate counts, respectively. The weight loss ratio was the lowest for CHSTiO2/TT80 (10.88% loss) followed by CHSTiO2 (11.76% loss). CHSTiO2/TT80 recorded a higher electrolyte leakage rate (25.84%) and acidity. While the lowest PPO activity was established for CHSTiO2 (17.09 U mg−1 Protein), while the lowest values for total soluble solid concentrations were reported for CHSTiO2/TT80 mushrooms (4.91%). These results indicated that CHSTiO2/TT80 coating treatment might delay the aging degree of white button mushrooms and be investigated as a novel packaging material for other food products in the future.