Study On Physio-Biochemical Changes Associated With Browning And Browning Mechanism Of White Flammulina Velulina

The white Flammulina velutipes, an edible fungus which have riched nutritions, and high health-care values. With the improvement of lives quality, the demand of fresh Flammulina velutipes mushroom is increasing gradually. However, the respiration and metabolism of the post-harvest white Flammulina velutipes is abnormally strong, so deteriorates more rapidly either on sensory or nutritious quality. Among the changes of white Flammulina velutipes’quality, browning is the main factor of declining the quality of mushrooms. Now, there are few studies or researchers on the browning white Flammulina velutipes. In this experiment, the white Flammulina velutipes were selected as the materials to investigate the changes of the physiological and biochemical characteristics associated with browning during the storage,and the browning mechanism to offer the theoretical bases for the product development of fresh white Flammulina velutipes or other edible fungus. The results are as follows:1. During the storage of the white Flammulina velutipes, the browning degree BD,MDA constantly increased; the content of total phenol, Vc, and the white degree were constantly reduced.However, the sugar content and the respiratory rate increased first and then decreased. The enzymes which were related to the browning PPO, POD, PAL, SOD, all increased first and then decreased, CAT constantly reduced. According to the analysis of related indices, the conclusion were:the browning degree has significant related with MDA, total phenol, white degree, Vc and the PPO,POD. All These results indicated that these indices impacted the browning degree.2. The most suitable reaction temperature of Flammulina velutipes PPO was40℃; The most suitable reaction pH was5.5; EDTA-Na had apparent effects on decreasing the activity of PPO. The most suitable reaction temperature of POD was50℃; The most suitable reaction pH was5.5, Fe2+, Cu2+had apparent inhibition effect on POD. According to the thin layer chromatography of silica gel G, and HPLC-MS, showed that the main enzymatic browning substrates in white Flammulina velutipes was Chlorogenic acid. The cell ultrastructure of Flammulina velutipes from different stages of storage was observed by electron microscope, and it stated clearly that cell structure was broken gradually, the cell wall was degraded,the cell membrane was damaged,all the physiological indicators were broken down.