| Agaricus bisporus, with particular flavour, is not only delicious but also rich in nutrition. Due to high water content, delicate organization structure, intensive metabolic activity and unconspicuous protect layer, Agaricus bisporus easily gets intruded by fungus and machenical injury which causes browning and autolysis. It has a very short post- harvest life of 2-3 days at normal temperature.Such short shelf-life limits its long-distance transportation,marketing and consumption. Therefore, fresh-keeping technology of postharvest mushroom becomes is the key to the development of Agaricus bisporus production. The study of both the autolysis theory of Agaricus bisporus and the effect of different treatments on Agaricus bisporus autolysis were conducted systematically and the mathematical model of the autolysis theory was established in the paper. The results were as follows:1,Study of the characteristics of protease activities of Agaricus bisporusThe characteristics of protease activities of Agaricus bisporus which included catalytic characteristics, the optimum temperature, the optimum pH and the thermostability were discussed by Folin-phenol. The difference between protease activity in different part was also analyzed. The results showed that the optimum pH and temperature of Agaricus bisporus protease were 7.5 and 45℃respectively, and the protease was inactivated at 100℃for 30s. The reaction kinetic of protease hydrolyze casein was accordant to Michaelis-Menten. The Km andνmax were 1.1041*10-3 mol/L and 125.6 U/min respectively. The proteasee activity of pileus was higher than that of stipe.2,Effect of microorganism on Agaricus bisporus autolysisThe results showed that the stipe significantly elongated, the pileus was open, and brown patch appeared on the surface during storage. With the increasing of the storage time, the brown patch area was enlarging, the color was turning darker, and black juice was overflowing gradually. The inoculation tests suggested that the microorganism was not the direct cause of the Agaricus bisporus autolysis. The structure of Agaricus bisporus was damaged due to the autolysis. And the growth of the microorganism caused by the overflowing juice accelerated the decay of Agaricus bisporus.3,Effect of the senescence on Agaricus bisporus autolysisThe autolytic index and several important physiological and biochemical factors during the natural senescence process of Agaricus bisporus were measured. The results showed that the autolytic index, cell membrane permeability, the content of water-solubility pectin, MDA and O2-·increased significantly, while hardness, protein contain, protopectin, cellulose and moisture content decreased during senescence process. POD activity increased in early stage and decreased later. The autolysis of the Agaricus bisporus was closely related to senescence through the analysis of data pertinence. The change in organization structure of the Agaricus bisporus was examined during the storing periods with TEM.The results showed that with the increasing of the storage time, the organization structure was destroyed seriously, The main phenomenon was the disorganization of the mitochondria, vacuole, membrane system, cytoderm and other cellular organ, the release of the substrate in the cell. During the autolysis, the factors incruding the decline of POD and other oxido-reduction enzyme activity, O2-·increasing, caused membrane lipid peroxidation intensify, MDA content increase, cell membrane permeability increase. The degradation of the mitochondria, vacuole and other cellular organ caused the intracellular hydrolases (PG, Cx, protease) dissolve out and react to the substrate (protein, protopectin, cellulose).The increasing of the PG, Cx and protease activity led to the degradation of the protein, cellulose, protopectin, plus water lost caused plasmolysis.The degradation of the cytoderm and the increasing of the membrane permeability made the juice reactants overflow, hardness decline,eventually led to Agaricus bisporus soften,autolyze. Agaricus bisporus autolysis was a result of enzymatic reaction.PG, Cx and protease are the key enzymes in the enzymatic reaction.4,Study of the relation between the storage environment and Agaricus bisporus autolysisThe relation among different storing temperatures, gas components and Agaricus bisporus autolysis was discussed. The results showed that the autolysis index of the Agaricus bisporus had significant linear correlation to different temperatures, gas components. The autolysis velocity increased with the temperature and the oxygen content. The autolysis velocity was lowest as the oxygen content is 5%. Because of the lower oxygen content,the nitrogen-filled packaging caused anaerobic respiration, because ofwhich the epitermis of Agaricus bisporus turned yellow and accelerated the autolysis velocity.The autolisis index had significant difference among different temperature,moisture content. And also there existed difference between MAP and common packaging, but it didn't have significant difference among MAP of different oxygen contents. Optimun lower-temperature and MAP inhibited the degradation of protein, cellulose and enzymatic activity, defered the Agaricus bisporus autolysis.5,Study of the relation between the self difference and Agaricus bisporus autolysis The relation among different size, parts and Agaricus bisporus autolysis was discussed. Results showed that Agaricus bisporus autolytic index increased under different size,parts. The autolysis index had significant difference among different size, it didn't have significant difference among different parts. The autolysis velocity of Agaricus bisporus which the pileus diameter was 30~40 mm was slightly less than the pileus diameter was 20~30 mm and 40~50 mm. The content of protein, cellulose and the activity Cx, protease had significant difference among different size and parts. The protein content and protease activity of the pileus was higher than the stipe, but the cellulose content and Cx activity of the stipe was higher than the pileus. |
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