Design Of Walk-in Equipment And Comprehensive Technology For Volvariella Volvacea Postharvesting

Volvariella volvacea,known as the Chinese mushroom or straw mushroom,is a typical thermophilic mushroom originating in China.It keeps attracting the consumers’interest due to its unique flavor,texture and nutritional values.However,the harvested fresh fruiting body of V.volvacea still maintains strong respiration and metabolic activities,which results in the rapid deterioration of appearance and sensory quality（color,aroma and taste）within 24～48 hours.Additionaly,its fruiting bodies suffer the chilling damage with softening and liquefaction at below 10 ^oC,and rapidly brown and shrink at over 15 ^oC with shrinking appearance and lower nutritional components.Therefore,short storage period and extremely difficult postharvesting due to the low-temperature autolysis and high-temperature quality deterioration of V.volvacea significantly limit production capacity and long-distance distribution.Although previously ⁶⁰Co ray irradiation and addtion of chemical antioxidants have been attempted to prolong the shelf life of V.volvacea,high cost of equipment input,complex operation procedures and/or chemical preservative residues could not meet the requirment of low-cost,zero-chemical addition,and industrial scale application raised by the production companies.On the basis of the previous research of our group,the present study focuses on designing and optimizing a walk-in preservation equipment for postharvesting the tropical/subtropical edible fungi with high-precision temperature and humidity control,investigating the optimal operation parameters including rowth stage,precooling temperature,loading capacity and stacking mode to obtain the maxumum sensory attributes,physical/chemical qualities,and elucidating the potential mechanism on the basis of respiratory metabolism and energy balance,and activities and expression levels of the respiration associated enzymes.The outputs would potentially provide a reference for the develop a low-cost,zero-chemical addition,and industrial scale application of equipment and technology for V.volvacea posthavesting.The main results are obtained as follows:（1）A walk-in preservation equipment for postharvesting the tropical/subtropical edible fungi with control of high-precision temperature and humidity was designed based on the previous results,with the size of 2.9×1.5×2.0 m（length×width×height）,temperature ranging from-10℃to 60°C with accuracy of 1°C,humidity ranging from 0 to 100%RH with accuracy of 5%RH.The optimal ventilation and humidification were obtained as:ventilation velocity 7m/s,aperture area 2.7 cm²,water temperature 15°C,water level height 30 mm,distance between three ultrasonic humidifiers with one-line arrangement was 60 mm.Temperature and humidity of the walk-in preservation equipment rapidly reached to the predetermined value after operation for10 minutes in optimized condition,and showed a stability during 16-d continuous run.（2）The effect of growth stage（button,egg,elongation and maturity）,precooling temperature（including no precooling,25°C precooling and 20°C precooling）,loading capacity（large basket/LB of 14.40 kg,middle basket/MB of 10.40 kg,small basket/SB of 6.70 kg and extra small basket/XSB of 0.95 kg）and stacking mode（no stacking,one-layer of overlapping and two-layer of overlapping）on the quality of postharvest V.volvacea were well investigated with the desgined walk-in preservation equipment.The optimized comprehensive preservation conditions for V.volvacea was obtained as:freshing fruiting bodies at egg stage,temperature of15±1℃and humidity of 90±5%RH,loading capacity in small basket/SB 6.70 kg,precooling temperature 20℃with no stacking.Our results showed that V.volvacea stored in this walk-in equipment under the optimized condition significantly delayed the change of color,flavor and firmness,maintained the highest firmness（1.886 N）and acceptability（6.1）even to the 4 th day of storage,decreased the loss of weight（9.17%）,soluble protein（22.638 mg/g）,and soluble sugar（26.844 mg/g）,reduced MDA content（1.848 nmol/g）and PPO activity（70.25 U/g）,delayed the browning degree（0.565）and conducive to retard the sensory deterioration of V.volvacea.（3）The sensory quality and physicochemical properties,water status and distribution,respiration intensity,activity of key enzymes of respiratory metabolism and their transcriptional levels,mitochondrial H⁺-ATPase activity,ATP/ADP/AMP content and energy charge in fuirting bodies stored at 4℃,room temperature,and optimized conditions were compared.Results showed V.volvacea stored at optimized conditions maintained water loss（85.14%）on the 4 ^thday of storage with content of free water for 100%,reduced the loss of 1-octen-3-ol（0.0401mg/L）,maintained the respiratory intensity of 818.92 mg/kg·h and body temperature of 15.3℃,and decreased the activities of respiratory metabolism-related enzymes including SDH,CCO and PGI of V.volvacea to 2.39 U/mg·pro,13.81 U/mg·pro and 0.083 U/mg·pro,respectively,and transcriptional expression levels of vv PGI,vv SDH and vv CCO.The H⁺-ATPase activity,ATP,and ADP contents in the mitochondria of V.volvacea also decreased to 273.2 nmol Pi/min/mg prot,73.2μg/g and 36.6μg/g,respectively,with the highest level of energy charge of 0.56.The findings indicated that the the optimized comprehensive posthavesting conditions could delay the rapid deteriorationand senescence of fresh V.volvacea by moderately regulating its respiration metabolism and energy balance.