Study On The Microstructure Variation Of Seed Materials During Moisture Migration Under Low-Temperature Vacuum Environment

This article takes broad bean seeds as the research object,using microscopic imaging technology and image processing technology to study the dehydration kinetics of crop seeds under low temperature and vacuum environment,and quantitatively analyzes the changes in sample microstructure during water migration,including cell geometric parameters?diameter,Area,perimeter?and shape parameters?roundness,elongation,compactness?,changes in pore network structure?cell wall and cell gap?and the tendency of cell rupture accompanying this process.From the perspective of heat and mass transfer and biomechanical structure,the inner cell mechanism of structural deformation and damage at the micro level was discussed.In addition,a two-variable correlation analysis method is used to analyze the correlation between the above microstructure parameters and the sample's macroscopic characteristics?water content,shrinkage?.The above research gives a more comprehensive understanding of the microstructural changes during the low-temperature vacuum dehydration of broad bean seeds.It is of great significance for the subsequent establishment of a more accurate microscopic transportation model in the future and analysis of the heat and mass transfer phenomena at the cell level and the mechanism of cell deformation and damage to make up for the gaps in theoretical research in this aspect.The main research conclusions are as follows:?1?It has been found that the distribution of cell size and shape parameters of broad bean seeds changed significantly with dehydration time.The cell size was primarily affected by moisture content while cell shape by dehydration temperature as well as moisture content simultaneously.Compared to the situation at 0°C,the overall changes in cell size and shape distributions at 8°C were more uniform during dehydration,which were close to the normal distribution?skewness=0,kurtosis=0?.Despite the cell rupture occurred,higher temperature caused more cells to contract more clearly.Relatively smaller cells were less prone to shrinkage and deformation during dehydration and were able to withstand certain dehydration intensity,as opposed to large cells.?2?D/D₀ correlated well with moisture loss and shrinkage during dehydration with correlation coefficients more than 0.96 and it could be used as an adequate generalized microstructural change indicator to correlate with the selected apparent changes in physical properties?shrinkage or moisture content?.Different from D/D₀,most of correlation coefficients were less than 0.9 when R/R₀ was considered and the correlation was not strong.?3?In the process of low-temperature vacuum dehydration,as the water content of the sample decreases,in addition to the cellular deformation,the network structure of the broad bean seed pores has also undergone significant changes and experienced corresponding shrinkage and deformation.Although the porosity increased with the increase of dehydration time and the temperature was higher,the increase of porosity was more obvious.However,when the water content was the same,the effect of temperature on the porosity was not obvious;the porosity showed a downward trend at the beginning of dehydration.After the water content was less than 0.8,the porosity increased steadily with the decrease of water content.If intact broad bean seeds had been taken as samples,the porosity would have shown a similar trend with the change of water content.?4??FD/FD₀ increases with the decrease of water content,almost linearly,which means that as the dehydration process progresses,not only the water content gradually decreases,but also the pore network of the cells changes significantly.When dehydration temperature is high,the tendency of cell rupture is more obvious.The cell rupture makes the microstructure of the sample more disordered and irregular.This complex microstructure change is primarily reflected in the variation of the pore network structure,which can be directly reflected by the fractal dimension of pores,so the change in the fractal dimension is more obvious.