Biochemical Characteristics And Texture Deterioration Of Postharvest Coprinus Comatus

Coprinus comatus is a novel cultivated edible fungus,hailed as a new preeminent breed of mushroom.However,C.comatus is difficult to keep fresh at room temperature after harvest due to high respiration,browning,self-dissolve and lack of physical protection.This had led to large losses in production,storage and sales of C.comatus.Therefore,it is necessary to carry out in-depth and systematic research on the related substances,influencing factors and possible degradation mechanism.At present,there was litter report on related studies of C.comatus.In this paper,the samples of C.comatus stored for 0d,5d,10d,15d and 20d were selected for the determination of biochemical characteristic,samples stored for 0d,10d and 20d were observed by transmission electron microscopy and transcriptome sequencing.Physiological changes and cellular degradation of postharvest C.comatus were investigated.The study finds that:（1）Under 4℃ and 90%RH storage condition,the C.comatus stored for 5d showed a litter degree of browning,cap opening,and wilting.With the extension of storage time,the quality of C.comatus became worse.After 10 days of storage,mushrooms appeared acutely browning,cap opening and flowing black juice,rendering the mushrooms commercially unacceptab le.The study found that the browning was related to the high activity of PPO.The activity of SOD,CAT,POD gradually increased,peaked at the day 10.High SOD,CAT,POD activity could be beneficial in protecting cells from ROS-induced injuries,alleviating lipid peroxidation.The activities of chitinase andβ-1,3-glucanase were significantly increased.Higher degrees of cell wall degradation observed during storage might be due to the high activities of these enzymes.（2）Under the transmission electron microscopic examination,the fresh C.comatus had dense tissue and every single cell had the number of intracellular organelles which structure can be observed clearly.After 10d storage,the number of intracellular organelles was declined and the structure was fuzzy,the nucleus disappeared.After 20d storage,C.comatus’s organization was completely lost,many cells were stacked together and the cell wall was badly damaged.（3）RNA-seq analysis showed that in the glycolysis/gluconeogenic metabolic pathway,aldosterase genes（DN31810＿c0＿g1,DN31810＿c0＿g2）and 3-phosphorglyceraldehyde dehydrogenase coding genes（DN36464＿c1＿g7,DN27098＿c1＿g1）were upregulated,revealing that glycolysis were enhanced during postharth storage.And pyruvate decarboxylase gene（DN34058＿c0＿g1）was significantly upregulation,on the one hand,it leads to the intensified decomposition of pyruvate and the accumulation of acetaldehyde,thus damaging the cellular structure of C.comatus.On the other hand,it causes the accumulation of large amount of ethanol in the body of C.comatus and the emission of ethanol odor,thus reducing its edible and commercial properties.In addition,in the tricarboxylic acid cycle,the malate dehydrogenase gene（DN33407＿c0＿g2,DN31328＿c0＿g1）was significa ntly up-regulated,which promoted the synthesis of glyoxylic acid,and resulted in the accumulation of CO₂ in the mushroom body through the citric acid cycle,damaging the cells of C.comatus.The study also found that among the genes which encoding cell wall metabolic enzymes,the genes of chitinase A1（DN33884＿c0＿g1,DN36367＿c0＿g2）in the GH18 family were significantly down-regulated in the early stage of storage,and the genes of endochitinase（DN31800＿c0＿g1）in the GH19 family were significantly up-regulated in the late stage of storage.Theβ-1,3,β-1,4-glucanase（DN34667＿c0＿g1,DN36121＿c0＿g2）genes and the glucanase（DN35418＿c0＿g1）genes were also significantly up-regulated.Among them,the up-regulation of chitinase gene,β-1,3,β-1,4-glucanase gene revealed the accelerated decomposition of polysaccharides and the degradation of cell wall skeleton.The above genes play an important role in the cellular degradation of C.comatus after harvest.