Study On Storage Characteristics And Cell Deformation Of Fruits And Vegetables In Vacuum Precooling

In recent years,the production of fruits and vegetables is increasing,but the rotting problem of fruits and vegetables is still very serious.At the same time,people have higher quality requirements for fruits and vegetables.The above two aspects stimulate the rapid development of the vacuum pre-cooling technology.Pressure is one of the most important factors affecting the effect of vacuum pre-cooling.Under different pre-cooling final pressure settings,vacuum pre-cooling will affect not only the microstructure deformation of fruit and vegetable cells,but also the quality of fruits and vegetables during storage seriously.The main research contents of this paper are as follows:(1)Theoretical analysis of vacuum pre-cooling technology.In the process of vacuum pre-cooling,the heat and mass transfer takes place in the free water.The migration of free water consists of two parts: one is the migration of water under the effects of the temperature difference;the other part is the migration of the vapor caused by boiling water under the pressure gradient.Moreover,the latter dominates the vacuum cooling process.At the same time,the process of heat and moisture migration of food is briefly introduced,and the thermophysical parameters of different materials are given.(2)Effects of different pre-cooling final pressures on storage quality of Pleurotus eryngii.Pleurotus eryngii is treated as the research object,and the study is the relationship between different pre-cooling final pressures(800Pa,1000 Pa,1200Pa)and the storage quality of Pleurotus eryngii.The effect of pre-cooling pressure(800Pa)on the respiration rate and hardness of Pleurotus eryngii is significantly affected.Pleurotus eryngii is a kind of respiratory climacteric vegetable.After 800 Pa pre-cooling treatment,Pleurotus eryngii reaches the peak rate of respiration in advance,and the respiratory rate is greater than the other two groups.What’s more,it has the fastest consumption of nutrients,yet the experimental results of the other two groups are similar.Pectin is the main factor affecting the hardness of fruits and vegetables.1000 Pa and 1200 Pa pressure treatments can reduce the formation of hydrolytic enzymes and reduce the change of insoluble pectin into soluble pectin,so the hardness is obviously larger than 800 Pa treatment group.The pressure treatment of 1200 Pa has a great effect on the weight loss rate and cell membrane permeability of Pleurotus eryngii.The weight loss rate of Pleurotus eryngii is the highest under 1200 Pa pressure treatment,but it was not the same as that of the other two groups.Relative electrical conductivity is an important indicator of cell membrane integrity.The larger relative electrical conductivity is,the more serious the cell membrane is damaged.The relative conductivity of the Agaricus bisporus is higher than that of the other two groups on the 8th day,and it has a tendency to increase,indicating that some of the cells have been damaged.After the the comprehensive index test among weight loss rate,hardness,respiration rate,cell membrane permeability,the most suitable pre-cooling pressure of Pleurotus eryngii is 1000 Pa.(3)Effects of different pre-cooling final pressure on the deformation of Onion.How the macroscopical shape of fruits and vegetables performances depends on changes in microstructure.In this study,the onion epidermal cells are used as the object of study,and the changes of the main strain and the unit strain are measured by the digital image correlation method under different pre-cooling pressures.It is concluded that the main cell strain is mainly related to the morphology of the cell wall.The lateral change of the cells is contraction,and the longitudinal change is expansion.The reason is that the micro-stress acting on the cell wall due to the internal and external pressure difference of the cell wall changes the morphology of the cell,and the longitudinal micro stress is greater than that of the lateral direction.The expansion appears fistly,contraction followed in the shape of the cell unit.The reason is that the internal and external pressure difference of the cell is increasing through the whole experiment,and the micro-stress on the cell membrane is increasing.So the cell is inflated.However,due to the breakdown of some cell tissues,it results in cytoplasmic cohesion,and the cell swelling decreases,so the cells begin to shrink.