Development And Application Of Phase Change Coolant For Edible Fungi

Edible fungi deteriorate quickly after harvesting,which will cause serious waste and loss.Cold chain logistics is a supply chain system whose core requirement is to maintain a low temperature environment.It has a positive effect on the quality maintenance of edible fungi during storage and transportation.Phase change cold storage technology is very suitable for cold chain storage and transportation systems.Based on this,this paper aims to develop a phase change coolant based on the freezing point of edible fungi,using differential scanning calorimetry（DSC）to measure its thermal physical parameters,to develop a phase change coolant with appropriate phase change temperature（onset temperature）and high phase change latent heat,and is economical,safe and easy to use.Then,two typical edible fungi（Pleurotus eryngii and Shiitake mushroom）are selected to study the fresh-keeping effect of the developed coolant,in order to provide a theoretical basis for its further application in the storage and transportation of edible fungi.The main research contents and conclusions are as follows:（1）Aiming at the freezing point of edible fungi,with a phase change temperature of-2～-1℃and a phase change latent heat exceeding 280 J/g as the target,develop a phase change coolant with suitable phase change temperature and high phase change latent heat.Through the determination of the main cold storage substance,the addition of various compound substances,the optimization,the phase change temperature and the phase change latent heat measured by DSC,and the performance of the coolant tested,the final formula of the phase change coolant is:maltitol 1.72%,potassium sulfate 2.09%,nano titanium dioxide 0.01%,super absorbent resin0.50%,and the rest is water.Its phase change temperature is-1.64℃,phase change latent heat is295.14 J/g,in addition,it has no supercooling or phase separation,so it meets the expected goal.（2）Apply the developed phase change coolant in the storage and preservation of Pleurotus eryngii and Shiitake mushroom,and determine the basic freshness quality indexes and related nutrient substance indexes（free amino acid content and Glutamate-related metabolic enzymes）during storage.The results show that compared with the control group and the same amount of ice group,the coolant group can provide a low temperature environment suitable for the storage of Pleurotus eryngii and Shiitake mushroom more effectively.Among them,the Pleurotus eryngii coolant group can maintain about 26 h within the appropriate fresh-keeping temperature range of edible fungi,and about 65 h below room temperature.The Shiitake mushroom coolant group can maintain about 23 h within the appropriate fresh-keeping temperature range,and about 57 h below room temperature.The phase change coolant will not cause injuries like freezing damage of the edible fungi.Campared with the other two groups,the coolant group can best maintain the sensory characteristics,color and hardness of edible fungi,reduce the mass loss,the total phenols and flavonoids loss,maintain a high DPPH removal ability,and slow down the degradation of protein,therefore to delay their quality deterioration.In addition,the treatment with phase change coolant can also regulate the activity of Glutamate-related metabolic enzymes and better maintain the content of Glutamate,so the phase change coolant helps to keep the freshness of edible fungi.（3）The effect of phase change coolant on physiological and energy metabolism related indexes of Pleurotus eryngii and Shiitake mushroom during storage are also studied.The results show that the physiological activities of Pleurotus eryngii and Shiitake mushroom in the coolant group are basically higher than those of the control group and the ice group,which reduce the production of malondialdehyde and the increase of the cell membrane permeability,inhibits the activity of polyphenol oxidase and maintains higher antioxidant enzyme（SOD,POD,CAT）activity,effectively preventing the free radicals from damaging the cells.In terms of energy metabolism,the coolant group keeps a higher activity of H⁺-ATPase,Ca²⁺-ATPase,SDH,CCO,makes the content of ATP and ADP higher than the other two groups.On the 5th day of storage,the energy charge of Pleurotus eryngii control group,coolant group and ice group are 0.67,0.75and 0.68 respectively;the energy charge of Shiitake mushroom control group,coolant group and ice group are 0.43,0.63 and 0.48 respectively.It can be concluded that the treatment with phase chage coolant is more conducive to reducing energy loss,ensuring a higher energy supply in edible fungi,so it has a positive effect on maintaing the structural function of Pleurotus eryngii and Shiitake mushroom’s cell and biofilm,so as to delay their browing and aging.