Group Title: Citrus Station mimeo report - Florida Citrus Experiment Station ; CES 65-6
Title: The Cobalt-60 food irradiator at the University of Florida
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 Material Information
Title: The Cobalt-60 food irradiator at the University of Florida
Series Title: Citrus Station mimeo report
Physical Description: 4 leaves : ; 28 cm.
Language: English
Creator: Dennison, R. A
Citrus Experiment Station (Lake Alfred, Fla.)
Publisher: Citrus Experiment Station
Place of Publication: Lake Alfred
Publication Date: 1964
Subject: Citrus fruits -- Preservation -- Florida   ( lcsh )
Citrus fruits -- Radiation preservation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: R.A. Dennison.
General Note: Caption title.
General Note: "October 6, 1964."
 Record Information
Bibliographic ID: UF00072427
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 75969705

Full Text

Citrus Station Mimeo Report CES 65-6
October 6, 1964

The Cobalt-60 Food Irradiator at the University of Florida

R. A. Dennison
Department of Food Technology and Nutrition
University of Florida


There has been widespread interest in the use of high-energy ionizing
radiation as a processing tool. One of the potential applications is in the
preservation of food. There are two important approaches to preserving food
against microbial action by radiation, i. e., through sterilization and
pasteurization. The radiation dosages required for sterilization range from
approximately 2,000,000 to 6,000,000 rads and for pasteurization from 50,000
to 600,000 rads. Other ionizing radiation processes not involving antimi-
crobial action include inhibition of sprouting of potatoes and onions, disin-
festation of grain and flour and control of fruit ripening. In these cases,
low radiation doses in the range of 10,000 to 50,000 rads are sufficient.

The Division of Isotopes Development of the U. S. Atomic Energy Commission
is supporting studies on the pasteurization of fruits and vegetables and seafoods,
Through the Atomic Energy Commission, the University of Florida recently received
a Cobalt-60 research irradiator for studies on fruit pasteurization.

Fruit Deterioration

The spoilage losses of fresh fruits during normal marketing practices
usually represent a sizeable figure. Potential methods of reducing this loss
are of interest to anyone marketing and handling fruits as well as to the

Deterioration of fruits results from two causes: (1) decay caused by
microorganisms, and (2) self destruction by the natural physiological or life

Molds, yeasts and bacteria growing on fruits cause spoilage which results
in losses during the various steps in marketing and after the fruits get into
the hands of the consumer. In order to reduce these decay losses, it is
necessary to keep contamination by microorganisms at a minimum, destroy the
microorganisms present on the fruit, or hold the fruit under conditions that
will prevent the growth of microorganisms.

Because of the perishable nature of fresh fruits, there are certain
inherent marketing problems. Under the most ideal conditions, the length of
the marketing period is limited by the physiological changes occurring in
the fruits.

Food Technology and Nutrition Department,
University of Florida, Gainesville, Florida.
400 10/6/64 RAD

There are a number of postharvest treatments or handling methods in common
use which aid in the reduction of fruit spoilage. Temperature control has been
extremely important. The proper use of precooling, refrigeration in transit,
refrigeration storage and refrigeration at the retail store have all contributed
to quality maintenance. Most of the common decay organisms, at the lower
temperatures, are retarded in development. Metabolic changes of the fruit are
slowed down and senescence of the tissues is delayed. Supplemental treatments
with fungicidal and bactericidal agents for the control of decay organisms are
contributing to the reduction of spoilage. These are adjuncts to refrigeration
for the retardation of spoilage.

Any development that will aid in the maintenance of quality of fruits during
the marketing process is of interest to the fresh fruit industry. The use of
ionizing radiations may ultimately offer possibilities as a postharvest treatment
aiding in the maintenance of quality of fruits.

Ionizing Radiations and the Treatment of Fruits

Radiation from radioactive material is a stream of fast-moving particles or
waves from atoms. The invisible rays from radioactive elements are of three
kinds, namely, alpha, beta, and gamma. The gamma ray is an electromagnetic radi-
ation of extremely short wave length. It is a highly penetrating ray. The gamma
rays have the greatest potential use in the pasteurization of fruits. Beta
particles could be used to some extent in the surface pasteurization of fruits.

About 1946, Proctor and co-workers demonstrated that radiations were useful
in control of microorganism development. Since then much interest has been shown
in the potential of irradiation for food preservation.

For the most part, we can consider gamma rays from Cobalt-60 as the radi-
ation source for use with perishables. This radiation is very penetrating,
reaching deep inside the fruit and does not induce radioactivity in the commod-

Rays hit the organisms and cause damage or death to the cells. The number
of microorganisms a reaction dosage will destroy depends largely upon the number
of rays with which the material is bombarded and the number and size of the tar-
gets in the material. In order to get complete kill of microorganisms (sterili-
zation) very high doses of radiation are required. Complete sterilization with
high radiation doses is far beyond the tolerance of fruits. However, by the use
of low levels of radiation, a large percentage of the microorganisms can be

In radiation treatments, the rays also are striking the tissues of the
fruits as well as microorganisms and changes in these tissues must be considered.
Any undesirable changes in flavor, aroma, color, and texture are a disadvantage.
The physiological and biochemical changes must be critically evaluated in fruit
irradiation studies.

Food Technology and Nutrition Department,
University of Florida, Gainesville, Florida.
400 10/6/64 RAD

Feasibility of Fruit Irradiation

Radiation cannot work miracles even if it proves feasible. It may, with
some commodities, prove to be a beneficial supplement to conventional cold storage,
handling and marketing procedure.

In a study of the feasibility of fruit irradiation a number of problems must
be considered. Among these problems are the following:

1. What can be achieved by irradiation?

2. What are the technological problems with respect to the fruit itself?

3. What are the technological problems with respect to irradiators?

4. What are the economics of fruit irradiation?

In laboratory studies it has been shown that the spoilage caused by certain
microbial infections can be reduced. The potential role of radiation as an aid
to marketing fruits appears to be more that of reducing decay during the normal
marketing period rather than that of greatly extending the storage life.

Fruits are known to respond differently to irradiation depending upon
variety, maturity, environmental conditions during production, environment at
time of harvest (rainfall, temperature) and postharvest environmental conditions
(temperature, storage, humidity, sanitation). It is necessary to determine what
varieties respond satisfactorily to irradiation, what levels of irradiation are
safe to use and are necessary to be effective in microbial control.

The design of irradiators will be influenced by the amount of fruit to be
handled in a period of time, the irradiation dose required, the type and size of
package that can be used, whether a fixed or mobile source can be used and the
necessary auxiliary facilities for handling fruit. Factors in radiation safety
must be considered in the design and construction of any facility.

The economics of fruit irradiation is a critical consideration. It is
necessary to know the present economic losses by spoilage that might be prevented
by irradiation. If fruit spoilage were reduced with a resulting increase in
supply, how would this influence the economic returns? The value of each crop
must be considered and the location of production. If the crop is produced in a
fairly concentrated area, the planning for irradiation facilities would be much
different than for a crop that is produced over widely scattered areas. The
capital investment for a facility and cost of operating must be known.

Finally the irradiated fruits must be accepted by the consumers. Even if
all other factors are favorable, the use of irradiation will be defeated if
there is not market acceptance. The wholesomeness of irradiated foods has been
investigated for many products and the safety of these seems assured.

Food Technology and Nutrition Department,
University of Florida, Gainesville, Florida.
400 10/6/64 RAD


The Irradiation Facility

The AEC has had built and installed four of the food research irradiators
for pasteurization level studies. In addition to the one at the University of
Florida, these are located at the Massachusetts Institute of Technology, the
University of California at Davis, and the University of Washington.

The University of Florida irradiator is the pool type. The facility con-
tains approximately 30,000 curies of Cobalt-60. Strips of Cobalt-60 are doubly
encapsulated in 96 stainless steel tubes. These capsules are uniformly placed
in two source plaques located at the bottom of a 6" diameter by 11' 3" deep
stainless steel tank. The tank is filled with water which serves as a radiation
shield and is part of the safety system. There are three 14" X 18" X 6" water
tight chambers in which to place the food samples to be irradiated. A conveyor
system moves the chambers into and out of the radiation field. The center
chamber is provided with temperature control that can be maintained from 100F to
1500F. Each of the chambers has connections for introducing and removing gases
to provide any desired atmosphere during radiation. The dose rate at the center
of a 6" thick package of unit density material, placed in the center container,
will be approximately 400,000 rads/hour; similar packages in the outer container
will receive a dose of about 220,000 rads/hour at the same point.

The facility has a water treatment system consisting of filters, mixed
resin bed demineralizer, flowmeter, pump, pressure gauges, conductivity meter,
and control valves. The pressure gauges show when the filters should be re-
placed. The effluent water is continually monitored by the conductivity meter.
Dust or debris, which may collect on the surface of the water, is removed by a
water skimmer.

Two safety systems are in operation; a radiation area monitoring system
with two detectors and a liquid level device. One detector, located above the
water surface, measures the radiation level above the pool and actuates audible
and visual alarms upon detection of radiation. The other detector, placed at
the water treatment system, insures early warning of activity in the filters or
the resin bed, if a source encapsulation should fail. The liquid level device
automatically maintains the height of the water in the tank at a predetermined
level by actuating a solenoid valve conncected to the water supply. It operates
audible and visual alarms should the water level fall excessively.

Food Technology and Nutrition Department,
University of Florida, Gainesville, Florida.
400 10/6/64 RAD

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