Nutrient Loss 245
for 10 to 60 sec. The water is recycled, but because of the temperatures used (50 to
70°C) organisms that are washed off the product into the water do not survive.
8.9.2.1.2 Vapor Heat
Vapor heat was developed specifically for insect control. It is a method of heating
fruit with air saturated with water vapor at temperatures of 40 to 50°C to kill insect
eggs and larvae as a sanitary and quarantine treatment before fresh market shipment
(Animal and Plant Health Inspection Service, 1985). Heat transfer is by condensation
of water vapor on the cooler fruit surface. This procedure was first used to kill the
Mediterranean (Ceratitis capitata Wiedemann) and the Mexican (Anastrepha ludens
Loew) fruit fly in a chamber without forced air (Lurie, 1999). However, once ethylene
dibromide and methyl bromide came into use as inexpensive chemical fumigants,
vapor heat was abandoned. With the ban on use of ethylene bromide in 1984, and
the imminent removal of methyl bromide from use in 2010, the use of vapor heat
has resurfaced (Gaffney et al., 1990). In modern facilities, the vapor heat includes
forced air, which circulates through the pallets and heats the commodity faster than
vapor heat without forced air. The treatment consists of a period of warming
(approach time) that can be faster or slower depending on the commodity’s sensitivity
to high temperatures. This is followed by a holding period when the interior tem-
perature of produce reaches the desired temperature for the length of time required
to kill the insect. The last part is the cooling down period, which can be air cooling
(slow) or hydrocooling (fast). There are thus a number of components of the treat-
ment that can be manipulated to obtain the best combination for elimination of the
insect pest with little to no damage of the commodity.
8.9.2.1.3 Hot Air
Hot air has been used for both fungal and insect control and to study the response
of commodities to high temperatures. Hot air can be applied by placing fruit or
vegetables in a heated chamber with a ventilating fan or by applying forced hot air
where the speed of air circulation is precisely controlled. Hot air, whether forced or
not, heats more slowly than hot water immersion or forced vapor heat, although
forced hot air will heat the produce faster than a regular heating chamber. The hot
air chamber has been utilized to study physiological changes in fruits and vegetables
in response to heat and to develop quarantine procedures (Gaffney and Armstrong,
1990; Klein and Lurie, 1992). The high humidity in vapor heat can sometimes
damage the fruit or vegetable being treated, while the slower heating time and lower
humidity of forced hot air causes less damage. A high temperature, forced air
quarantine treatment to kill the Mediterranean fruit fly, melon fly, and oriental fruit
fly on papayas has been developed (Lurie, 1999). This procedure may, however,
require rapid cooling after the heat treatment to prevent fruit injury, especially in
forced hot air treatment for citrus.
Exposure to high-temperature forced or static air can also decrease fungal infec-
tions. This requires long-term heating, from 12 to 96 h at temperatures ranging from
38 to 46°C, and is therefore unlikely to become commercially attractive. However,
the potential for hot air treatment to benefit commodity physiology, as well as prevent
both insect and fungal invasion, justifies further development of these treatments.