Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 86

and vermin in cereals. In 1981, the United Nation's Food and Agricultural Organi-
zation (WHO) endorsed irradiation doses up to 10 kGray, as a major technology for
the prevention of foodborne illness and for the reduction in food losses due to
spoilage by microorganisms and vermin. Ionizing radiation is now approved for use
in more than 41 countries for over 35 specified foods, and the list is growing. 2
Approximately 26 countries currently employ radiation on a commercial scale for
food application. 3 Over the last 10 to 15 years there has been a tremendous momen-
tum of research focused on the use of irradiation and foods. Pertinent worldwide
data, both published and unpublished, have been reviewed extensively and it has
been concluded that foods which are approved for radiation treatment pose no greater
health risks with regard to their radiological, toxicological, and microbiological
safety and are as wholesome in terms of nutritional adequacy as those treated using
conventional intervention strategies. 4-7
In this chapter the use of radiation will be examined specifically as it relates to
the shelf life extension of foods. For the most part this will involve an overview of
its use in reducing the level of spoilage microorganisms in food commodities and
altering postharvest ripening and senescence of fruits and vegetables. Many patho-
genic microorganisms including spore formers such as Clostridium botulinum are
also known to contribute to food spoilage. Although the presence and survival of
pathogens in foods is of great importance from a health hazard standpoint, their
involvement will be discussed mainly in reference to food deterioration leading to
shortened shelf life. In addition, the use of radiation in combination with various
other preservative techniques, including heat and modified atmosphere packaging
(MAP), will be reviewed.
IRRADIATION
I RRADIATION R ESISTANCE OF M ICROORGANISMS
Overwhelming evidence has been brought forward to indicate that the shelf life of
most foods can be extended safely by radiation treatment. In part, this is due to a
reduction in the original number of spoilage microorganisms associated with the
food. 8,9 Factors affecting the radiation resistance of microorganisms in foods are
therefore of paramount importance especially considering that maximum dose rates
are mainly influenced by sensory attributes. The irradiation resistance or sensitivity
of a microorganism is commonly given as the D 10 dose. This is the dose that is
required to kill 90% of a population. The radiation dose unit, previously referred to
as the rad, is currently known as the Gray (Gy). The Gray is the absorption of 1 joule
of energy/kg irradiated material and is equivalent to 100 rads; 1 krad equals 10 Gy
and 1 Mrad equals 10 kGy. The irradiation resistance of spoilage microorganisms,
some of which are also pathogenic, varies and is dependent on several factors. 10,11
These factors should be considered prior to the application of treatment in order to
maximize preservative benefits. For example, foods containing high populations of
radiation resistant bacteria such as Deionococcus (previously referred to as Micro-
coccus : M. radiodurans ) and the psychrothrophic Moraxella-Acinetobacter group
require relatively high application dosages. Their D 10 values can be greater than