Study On Fresh-keeping Refrigerated Technology And Microbial Spoilage Of Volvariella Volvacea

The straw mushroom(Volvariella volvacea),is favored by people for its fresh scent and delicious taste.However,the straw mushroom is one type of typical high-temperature mushrooms that are mainly planted in summer.The straw mushroom would be pileus expansion after hours after picking at high temperature,and is easily to be subjected to autolysis at low temperature.Therefore,it is extremely important to study its fresh-keeping refrigerated technology.In this paper,the straw mushroom fresh-keeping refrigerated technology and the microbial spoilage of straw mushrooms during storage were studied.The main research contents and results are as follows:1.The selection of the optimum storage temperature of the straw mushrooms.The straw mushroom samples were stored in cold room at(12±0.5)℃,(14±0.5)℃,(16±0.5)℃,(18±0.5)℃ and(20±0.5)℃,respectively.The effects of different storage temperatures on the physicochemical indexes,such as respiration intensity,weight loss rate,browning degree,soft rot rate,soluble sugar content and soluble protein content of the straw mushrooms,were studied.The results showed that the straw mushrooms were slightly autolyzed after 24 hours of storage at both 12℃ and 14℃.When stored at 18℃ and 20℃,the straw mushrooms exerted greater respiration intensity and larger nutrient consumption,the straw mushroom stored at 20℃ tost their edible value after 36 hours,while their fruiting body shrinked with the abnormal odor at the late period of the storage at 18℃.However,the quality of the straw mushrooms stored at 16℃ was better than that of other groups stored at other temperatures,they remained edible when stored for 48 hours.Therefore,within the experimental temperature range tested in this study,16℃ would be the best storage temperature for the straw mushrooms.2.Effect of proper dehydration on refrigerated storage quality of the straw mushrooms.The heat pump dehydration equipment was used to remove some water from straw mushroom to achieve the different dehydration levels including 5%,10%,and 15%.The effects of different dehydration amount on refrigerated preservation quality of the straw mushrooms were studied under the condition of 16℃.The results showed that proper dehydration could prolong the storage time of the straw mushrooms.Among the samples of three different dehydration levels,the straw mushrooms with 10%dehydration exerted the best storage quality and the storage time could be up to 5 days,which was 3 days longer than the control group.After 5 days of storage,the weight loss rate(4.43%)and malondialdehyde(56.38nmol/g,dry basis)of straw mushroom with 10%dehydration level were all lower than those of the other groups;while soluble solids(5.15%),soluble protein content(7.86mg/g)were both higher than the other groups.Also the samples with 10%dehydration had no peculiar smell,and still had their own fresh scent at the fifth day of storage.3.Effect of modified atmosphere packaging with different initial gas compositions on refrigerated storage quality of the straw mushroom.The samples were divided into five groups and packed with the following gas components:high oxygen packaging:100%O2;medium oxygen packaging:50%O2+50%N2;low oxygen packaging:5%O2+5%CO2+90%N2;Control group 1:air sealing;Control group 2:perforating after air sealing.The effects of modified atmosphere packing on preservation quality of the straw mushrooms were studied under the condition of 16℃.The results showed that high oxygen packaging was more suitable for the storage of the straw mushrooms.Compared to high oxygen packaging,straw mushrooms of low oxygen packaging group and CK1 group would be subjected to anaerobic glycolysis,which affected the mushroom flavor.The samples of medium oxygen packaging was also subjected to such reaction at the late stage of the storage,while the samples of CK2 group began to deteriorate at the third day of storage.High oxygen packaging could effectively inhibit the moisture loss of the straw mushrooms,maintain good quality of their own characteristics,so the straw mushrooms of this group still kept good product quality on the fourth day of the storage.4.Isolation and identification of cultivable microorganisms during the storage of the straw mushroom and effects of microbial infection on the storage quality of the straw mushroom,The results showed that the culturable dominant bacteria during the storage of straw mushroom mainly included Pseudomonas sp.and Serratia sp.,and a small amount of Streptomyces sp.;Results of infection test showed that Pseudomonas sp.and Serratia sp.would aggravate the loss of water in the straw mushrooms and affect the mushroom flavor.The infection of Serratia sp.was more detrimental to the storage quality of the straw mushrooms than that of Pseudomonas sp..Therefore,further studys could be done to prevent the microbial spoilage from these two kinds of bacteria later.