What is vapor heat?
Vapor heat was developed specifically for insect control. The temperature and exposure time are adjusted to kill all stages of fruit fly infected produce (mango). The treatment consists of a period of warming (approach time) which can be faster or slower depending on a commodity’s sensitivity to high temperatures.
What is the holding period for insecticide?
Then there is a holding period when the interior temperature of the produce reaches the desired temperature for the length of time required to kill the insect.
Abstract
Postharvest heat treatments lead to an alteration of gene expression and fruit ripening can sometimes be either delayed or disrupted. The extent of the alternation of fruit ripening is a function of the exposure temperature and duration and how quickly the commodity is cooled following the heat treatment.
1. Introduction
Heat treatments (thermotherapy) have been used for over a century to free plant materials from pathogens, the temperature and exposure duration having been determined empirically ( Grondeau and Samson, 1994 ).
3. Temperature stress
The transfer of plants to an elevated temperature produces stress. The severity of stress is primarily determined by the temperature differential and the duration of exposure ( Lurie, 1998 ). Other factors such as rapidity of the change in temperature and the previous growing conditions are also important.
4. Response to heat treatment
The gross cytological changes that follow high temperature exposure (>45°C) have been described ( Belehradek, 1957) and include coagulation of the cytoplasm, cytolysis, nuclear changes and altered mitosis. Protoplasmic streaming is inhibited, and there is increased protoplasmic viscosity and a loss of membrane permeability ( Alexandrov, 1977 ).
5. Mechanism of responses to high temperature
HSPs produced in response to high temperature are believed to prevent irreversible protein denaturation that would be detrimental to the cell ( Parsell and Linquist, 1993) and this activity may be enhanced in plants by small HSPs ( Lee and Vierling, 2000 ).
6. Conclusions
Changes in fruit ripening during and following heat treatments can be divided broadly into two types ( Table 3 ). The first type of response is the normal stress cellular responses that lead to modification of chilling sensitivity, delayed or slowed ripening and some slight modification of quality.
Acknowledgements
We thank Mrs Gail Uruu and Dr Ching Cheng Chen for technical help. This is the College of Tropical Agriculture and Human Resource, Journal Series ♯4490.
How does vapor heat work?
Heat transfer is by condensation of water vapor on the cooler fruit surface . This procedure was first used to kill Mediterranean ( Ceratitis capitata Wiedemann) and Mexican ( Anastrepha ludens Loew) fruit fly ( Hawkins, 1932; Baker, 1952) in a chamber without forced air. 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 dibromide in 1984, and the imminent removal of methyl bromide from use in 2010, vapor heat has again come into use ( Gaffney et al., 1990 ). However, in modern facilities the vapor heat includes forced air which circulates through the pallets and heats the commodity more quickly than vapor heat without forced air. Commercial facilities operate in many countries, mainly for use on subtropical fruits, particularly mango and papaya ( Paull, 1994 ). In addition, studies have been conducted for using vapor or moist forced air to disinfest many fruits and vegetables from various insect pests ( Shellie and Mangan, 1993; Shellie et al., 1993; Shellie and Mangan, 1994b ).
What are post harvest heat treatments?
Postharvest heat treatments are being used for disinfestation and disinfection of an increasing variety of crops, including flowers, fruits and vegetables. This review focuses on the effects of heat on the commodity and its postharvest quality. The effects of a postharvest heat treatment on aspects of ripening and development of thermotolerance is discussed. Ethylene production, respiration, softening, color change and taste components such as soluble solids, acidity and volatiles are dealt with. Heat treatment induction of thermotolerance, both to high and low temperatures, so as to prevent heat injury and chilling injury is discussed, as well as the possible mechanisms of action of this response. Heat damage manifestations from unsuccessful treatments are described.
How does hot air work?
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 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 ( Klein and Lurie, 1991, Klein and Lurie, 1992a ).