Agriculture Reference
In-Depth Information
effectiveness of hot-water treatment in inactivating pathogens on seeds may be due
to the use of different inoculation methods (naturally contaminated versus artifi cially
inoculated, and the drying times after inoculation)
Considerations for the Commercial Application of Hot-Water Treatment
Several studies (Delaquis and others 2000; Li and others 2001b; Ukuku 2006) have
demonstrated that microorganisms on fresh fruits and vegetables that survived or
recontaminated after hot-water treatments grew faster than those on cold-water-
treated fruit during storage, particularly under abusive (higher) storage temperature.
Therefore, it is essential to avoid recontamination of fruits after hot-water treatment.
Furthermore, the fruits should be stored at temperatures that prevent the growth of
pathogens.
In addition, when warm fruit is immersed in cold water, the transitory pressure
difference resulting from the temperature differential between the fruit and water (i.e.,
warm fruit and cold water) can lead to infi ltration and internalization of bacteria (if
present) into fruit such as apple, orange, tomato, and mango (Bordini and others 2007).
Therefore, if the fruit is cooled with water after heat treatment, the cooling water must
be treated with a sanitizing agent to assure that it is free of pathogens. If the hot-
water-treated fruit is processed into fresh-cut products without cooling, the peelers,
knives, cutting boards, and other contact surfaces have to be sanitized to avoid
recontamination.
The sensitivity of produce to heat injury will limit the application of thermal treat-
ments. The sensitivity of fresh fruits and vegetables varies with the insulating proper-
ties; thickness and resistance to heat damage of the skin; and the growing conditions,
cultivar, maturity, rate of heating, and subsequent storage (Paull and Chen 2000). For
example, mature tomatoes are more susceptible to heat injury than the less mature
fruit (Sapers and Jones 2006). As a result, whether thermal treatment can be applied
to a specifi c commodity has to be studied individually with consideration of growing
condition, maturity, etc.
Microwave, RF, and Infrared
Microwave, RF, and infrared are systems of electromagnetic radiation that can be used
to generate heat in a material. Therefore, energy can be transferred from the generators
to a material without direct physical contact. The microwave frequencies allocated by
the Federal Communications Commission (FCC) for the purposes of heating are 2450
and 915 MHz. The 2450 MHz frequency is primarily used for home ovens; 915 MHz
is often used in commercial applications. RF is allowed at 13.56, 27.12, and 40.68 MHz.
Two mechanisms are primarily responsible for microwave and RF heating: dielectric
heating and ionic heating. The primary benefi t of microwave and RF heating is that
they can penetrate into the foods and require less time to come up to the desired
process temperature than conventional heating in which heat is mainly transferred by
conduction. Other advantages of microwave and RF heating systems are that the ener-
gies can be turned on or off instantly and the product can be pasteurized after being
packaged (Datta and Davidson 2000). Microbial inactivation kinetics for microwave
and RF are essentially the same as those of conventional thermal processing.
Search WWH ::




Custom Search