Effect Of Electron-beam Generated X-ray Pretreatment On Postharvest Storage Quality Of Agaricus Bisporus

Agaricus bisporus is favored by consumers owing to its wide planting area,various nutrients and good antioxidant activity.However,lack of cuticle on the surface of Agaricus bisporus,it is susceptible to mechanical damage and microbial contamination after harvest.As a respiratory leap type edible fungus,Agaricus bisporus usually undergoes a series of quality changes during postharvest storage,such as water loss,softening,browning,loss of flavor,and nutritional value,resulting in a decrease in its commercial value.Electron-beam generated X-ray technology is a new type of green and safe physical technology,which plays an active role in the storage quality of fruits and vegetables.To explore the effect of electron-beam generated X-ray pretreatment on postharvest storage quality of Agaricus bisporus,this study used different electron-beam generated X-ray irradiation doses to pretreat Agaricus bisporus,and unirradiated Agaricus bisporus was used as a control.The effects of irradiation dose on the physiological quality and antioxidant activity of Agaricus bisporus during storage were investigated,and the irradiation dose suitable for postharvest storage and preservation of Agaricus bisporus was selected.Furthermore,the effect of optimal electron-beam generated X-ray dose on epidermal cell wall metabolism of Agaricus bisporus during storage was explored.The main contents and results were as follows:Firstly,the effects of electron-beam generated X-ray pretreatment at different irradiation doses（0,0.5,1.0,1.5 and 2.0 k Gy）on the appearance,browning index,weight loss rate,firmness,respiration rate,microbial number,TSS content,soluble sugar content and sensory quality of Agaricus bisporus during low temperature storage were investigated.The results showed that compared with unirradiated Agaricus bisporus,1.0 k Gy electron-beam generated X-ray pretreatment effectively delayed browning degree of Agaricus bisporus,maintained good appearance quality.After 21 days of storage,the weight loss was 5.87%lower than that of the control group,the firmness was 43.68%higher than that of the control group,the contents of Pseudomonas and mold were 35.39%and 39.29%lower than those of the control group,and TSS and soluble sugar content were 16.1%and 18.02%higher than those of the control group.In addition,1.0 k Gy electron-beam generated X-ray pretreatment also obviously slowed down the respiration rate in the early stage of storage,inhibited the consumption of soluble sugar during the whole storage process,improved the sensory evaluation score,thus improving the physical and chemical qualities of Agaricus bisporus at4°C.Secondly,the effects of electron-beam generated X-ray pretreatment at different irradiation doses（0,0.5,1.0,1.5,and 2.0 k Gy）on membrane permeability,MDA content,PPO activity,total phenol content,SOD and CAT activity,DPPH·scavenging activity,O₂^·-production rate and VC content of Agaricus bisporus during low temperature storage were investigated.The results showed that compared with the control group,1.0 k Gy electron-beam generated X-ray pretreatment significantly reduced cell membrane permeability and MDA content of Agaricus bisporus during storage,passivated PPO activity,maintained a higher total phenol content,increased SOD and CAT activity,inhibited the decrease of DPPH·clearance rate,slowed down the production rate of O₂^·-and increased VC content,thereby improving the antioxidant activity of Agaricus bisporus at 4°C.Thirdly,the contents’changes of epidermal cell wall components（β-glucan,chitin,cellulose,lignin）of Agaricus bisporus after 1.0 k Gy electron-beam generated X-ray pretreatment during storage were investigated.The enzyme activities（β-1,3 glucanase activity,chitinase activity,cellulase activity,PAL activity）and the relative expression of genes regulating enzyme activities（Glu1 relative expression,Chi1 relative expression,Cel1 relative expression,PAL1 relative expression）were studied.In addition,the changes of epidermal ultrastructure of Agaricus bisporus after 21 days of low temperature storage were observed by scanning electron microscopy.The results showed that compared with the control group,1.0k Gy electron-beam generated X-ray pretreatment inhibited the activities ofβ-1,3 glucanase,cellulase and PAL by down-regulating the gene expression of Glu1,Cel1 and PAL1,thus increasing the contents ofβ-glucan and cellulose in the cell wall of Agaricus bisporus and reducing the content of lignin.It also reduced the degradation of chitin by inactivating the activity of chitinase.Scanning electron microscopy also proved that 1.0 k Gy electron-beam generated X-ray pretreatment effectively maintained the integrity of Agaricus bisporus cell wall during storage.In summary,1.0 k Gy electron-beam generated X-ray pretreatment can effectively maintain the quality of Agaricus bisporus during low temperature storage.It inhibits epidermal browning by passivating polyphenol oxidase system and activating antioxidant enzyme system.Meanwhile,it delays cell wall degradation by regulating the gene expression of enzyme system related to cell wall component degradation,maintains the firmness of Agaricus bisporus,and thus maintains the overall quality of Agaricus bisporus at 4°C.