Impact of ice crystal development on electrical impedance characteristics and mechanical property of green asparagus stems

The effects of ice crystal formation during freezing using three different methods: slow freezing, air blast freezing and liquid nitrogen spray freezing on the cell membrane state and mechanical property of asparagus stem samples were investigated. X-ray computed tomographic analysis revealed coarser ice crystal growth with slow freezing compared to the rapid freezing methods, which were characterized by fine and homogeneous ice crystal growth. However, electrical impedance analysis clarified that the structural damage and functional decline of cell membranes occurred regardless of the freezing method. Further, the elastic property of each frozen sample declined greatly after thawing and showed little improvement with rapid freezing. These results suggest that the reduction in turgor pressure following changes in the cell membrane state, attributable to the formation of ice crystals during freezing, is a major factor in the mechanical property, and this phenomenon is independent of the freezing rate and ice crystal size.