Understanding Freezing Injury in Plants

Freezing injury and chilling injury are both types of low-temperature damage that affect plants and agricultural produce, but freezing injury specifically occurs when temperatures drop below the freezing point of the product. For freezing injury to happen, the temperature must be below 32 °F (0 °C), causing ice crystals to form within the tissues of fruits or vegetables.

In plant tissues, water doesn't freeze exactly at 32 °F due to the presence of dissolved salts like plant sap, lowering the freezing point slightly. When temperatures plummet, ice crystals start to form within the cells, leading to the rupture of cell walls and rapid changes in tissue structure. This damage can occur rapidly within a few hours, affecting specific spots or the entire commodity. Affected tissues often appear water-soaked, with symptoms including browning, blackening, and wilting or curling of leaves and stems.

Notably, younger plant tissue is more susceptible to freezing injury than mature tissue due to its higher water content. To mitigate such damage, proper refrigeration or cooling techniques are essential. Refrigeration involves reducing and maintaining the temperature of food during storage, transport, and retailing. Rapid freezing is crucial as it prevents the formation of large, disruptive ice crystals that can damage cell structure upon thawing. In quick freezing, the molecules don't have time to align into large, damaging ice crystals, resulting in better quality preservation.

Conversely, slow freezing leads to the development of larger ice crystals that can harm cells and dissolve emulsions within the tissues. As a result, during thawing, the damage becomes more pronounced, affecting the texture and integrity of the produce.

Modern freezing technologies like cryogenic freezing and ultra-rapid freezing techniques have further revolutionized food preservation by minimizing the size of ice crystals, preserving the quality, texture, and nutritional value of frozen products. These advancements are critical in maintaining the integrity and quality of frozen produce, ensuring minimal freezing injury and better consumer satisfaction.
Understanding Freezing Injury in Plants