Physical changes in frozen fruits and vegetables

With the popularization of refrigeration equipment, frozen food has gradually entered people's vision. Previously, we introduced a lot of small knowledge about frozen fruits and vegetables. Today, our introduction is still related to frozen fruits and vegetables. Let's understand the physical changes that occur during the process of freezing vegetables and fruits.
1. The breakdown of cells.
As is well known, vacuoles are cells containing a large amount of water that exist in plant tissues. During the freezing process, it is easy to freeze into large ice crystals, generating significant pressure and making cells susceptible to rupture and damage. On the other hand, the cell walls of plant tissues are relatively thick and lack elasticity, making them easily punctured or swollen by large ice crystals. Freezing treatment increases the permeability of cell membranes or walls to water and ions. In the case of slow freezing, ice crystals mainly form in the intercellular space, causing protein denaturation or irreversible coagulation. Water inside the cell continuously flows out, and the concentration of inorganic salts in the protoplast continuously increases.
2. Mechanical damage.
The first to form ice crystals is free water in the intercellular space, which generally contains less soluble substances and has a high freezing point. However, the intracellular protoplasts remain in a supercooled state, and the supercooled water inside the cell has a higher vapor pressure and free energy than the extracellular ice crystals, which promotes the movement of intracellular water towards the intercellular space and continuously binds to the ice crystal nucleus in the intercellular space. At the same time, the ice crystals formed in the intercellular spaces become larger and larger, causing mechanical compression and separation of previously bound cells. After thawing, they cannot return to their original state, cannot absorb the water produced by the melting of ice crystals, and flow out juice, resulting in tissue softening.