Electrical and rheological analysis of freezing injury of agricultural products

Changes in electrical and rheological properties of cell tissues after freezing-thawing were measured to clarify the mechanism of freezing injury of agricultural products. The electrical property represented the state of cell plasma membrane and was measured by impedance with frequency varied from 0.1 to 1 MHz. The rheological property, measured by the vibrating reed method, showed changes in the state of cells. In the freezing of carrot tissue, the dynamic elasticity and viscosity were fairly sensitive to the loss in turgor pressure caused by the injury on the plasma membrane, through the intracellular ice crystal formation. Among eight kinds of different agricultural products after freezing-thawing, the dynamic elasticity and viscosity showed a good correlation with each other and positive correlations with crude fiber content. This suggests that the major determinants of the dynamic viscoelasticity of frozen-thawed samples are the mechanical properties of the cell wall and the intercellular structure.