Study On Browning Reason And Keeping Freshness Technique Of Pleurotus Geesteranus

Fresh Pleurotus geesteranus is a kind of mushroom which is edible，delicious andriched in protein. They have a very high water content and high respiration rate，whichmake the Pleurotus geesteranus tend to exhibit browning. That is a severe problem whichreduces the shelf life of harvested mushrooms. Thus，this thesis was discussed the browningreason of Pleurotus geesteranus，and studied the effects of different pre-cooling methods，storage temperatures，modified atmosphere packages on the storage quality of Pleurotusgeesteranus. The purpose is to provide a theoretical basis and technical support for thestorage of Pleurotus geesteranus. The results are as follows:1Studies of the reason of Pleurotus geesteranus browningDuring the storage at （15±0.5）℃，the results of relevance analysis between MDAcontent，PPO，POD，CAT activity，total phenols，reducing sugars，Vc content and coloris showed that browning included not only enzymatic browning but also the destruction ofthe cell membrane structure，and the reduction of reducing sugar might promote browningin the late storage stage. The results of Path analysis suggested that MDA，PPO，POD andtotal phenol affected browning significantly. The interactions of MDA and POD led to thedestruction of the cell membrane structure which was the prerequisite for enzymaticbrowning. The key enzyme was POD，and its dominant role was the ability of scavenge freeradicals in the early stage. Then，because of the destruction of the cell membrane structure，POD catalyzed phenol and the ability of scavenging free radicals was decreased.Accumulation of free radicals in turn exacerbated the membrane structure and led tobrowning further.2Studies of different pre-cooling methods on storage quality of Pleurotus geesteranusThe effects of different pre-cooling methods on both the cooling velocity and variousquality indexes of Pleurotus geesteranus were studied. The results showed that the coolingrates were affected significantly by different pre-cooling modules. Vacuum pre-coolingwithout moist treatment could cool Pleurotus geesteranus from23.5℃to5.6℃within20min，Combined with low temperature storage，this group demonstrated the best storage efficiency: color，soluble solids，total sugar and protein nutrition were higher than those ofthe other groups. After12days of storage，it still had the best sensory quality andcommercial value，and extended the shelf-life3d more than that of cold storage pre-cooling.3Influences of different temperatures on the storage quality of Pleurotus geesteranusStorage temperature was one of the main factors that affected post-ripening andqualities. This research showed that （-1±0.5）℃inhibited respiration rate，weightloss,value of L and membrane permeability of Pleurotus geesteranus. But about60%of thesurface of Pleurotus geesteranus exhibited ice，so-1℃was not the optimum temperature.Comparing to other different temperatures，（1±0.5）℃could observably reduce weight loss，respiration rate， soluble protein, PPO activity and could preserve the cell membranestructure，POD activity of Pleurotus geesteranus. It still had good sensory quality andcommercial value after15days of storage.4Influences of MAP on storage quality of Pleurotus geesteranusThe results of single-factor experiments showed that8%O₂treatment and25%CO₂treatment could preserve color，the cell membrane structure，and POD activity of Pleurotusgeesteranus. Four factors and three levels of the orthogonal experiment results showed thatthe optimum conditions were5%O₂，25%CO₂，（1±0.5）℃. In this conditions，it still hadgood commercial value after23days of storage.