Produce Degradation Pathways and Prevention

632 Produce Degradation: Reaction Pathways and their Prevention

Table 20.6 groups vegetables and fruits according to their freezing susceptibility.
Freezing injury is the direct result of unintentional freezing of fresh tissue. Mere
exposure of living tissue to temperatures below the freezing point does not neces-
sarily result in injury.^31 Supercooling of some produce to –10°C has been observed
without ice formation. However, agitation of a supercooled item can result in ice
formation, which is the primary cause of freezing injury. Prevention of freezing
injury is best achieved by maintaining storage temperature above the freezing point
of the commodity in question. When temperatures have cycled below the freezing
temperature, the most prudent action is to bring the tissue temperature above freezing
slowly before surveying the possible damage.
Freezing injury is often associated with chilling injury since both occur as a result
of exposure to low temperatures and both are characterized by loss of membrane
permeability and altered metabolic activity.^35 Some changes in lipid composition, bio-
physical properties, and altered enzyme activities also are common to both chilling and
freezing injury. However, there are differences between the two types of injury.
Freezing injury occurs when the contents of the cell freeze, causing ice crystals to
form in the tissues.^29 The most common symptom of freezing injury is a water-soaked
appearance (Figure 20.15). Tissues injured by freezing generally lose rigidity and

TABLE 20.6
Susceptibility of Fresh Fruits and Vegetables to Freezing Injury

Most Susceptible Moderately Susceptible Least Susceptible

Apricots
Asparagus
Avocados
Bananas
Beans, snap
Berries (except cranberries)
Cucumbers
Eggplant
Lemons and limes
Lettuce
Okra
Peaches
Peppers, sweet
Plums
Potatoes
Squash, summer
Sweet potatoes
Tomatoes

Apples

Broccoli

Carrots

Cauliflower

Celery

Cranberries

Grapefruit

Grapes

Onions (dry)

Oranges

Parsley

Pears

Peas

Radishes

Spinach

Squash, winter

Beets

Brussels sprouts

Cabbage, mature and savory

Dates

Kale

Kohlrabi

Parsnips

Rutabagas

Salsify

Turnips

Source: Wang, C.Y., Chilling and freezing injury, in The Commercial Storage of Fruits, Vegetables, and
Florist and Nursery Crops, Gross, K.C., Yang, C.Y., and Saltveit, M., Eds., Agricultural Research Service,
Beltsville, MD, 2002, draft version of revised USDA Agriculture Handbook 66, available at
http://www.ba.ars.usda.gov/hb66/index.html. (With permission.)