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STERILIZATION AND
PRESERVATION BY IONIZING
IRRADIATION
I MADE S. UTAMA
JURUSAN KETEKNIKAN PERTANIAN
FAKULTAS TEKNOLOGI PERTANIAN
UNIVERSITAS UDAYANA
INTRODUCTION





Research directed toward the use of radiation for the
preservation of foods begun in 1945.
Massacusetts Institute of Technology, The United States Army,
Quartermaster corps, The Federal Research Center for Food
Preservation (Germany), Michigan State University.
Radiation is not a widely used preservation method.
FDA; Food and Drug Law classifies radiation as a food
additive. Therefore, this has demanded an animal testing
program for establishing safety of process.
The two commercial application: preservation of food and
sterilization of medical products.
INTRODUCTION


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It has limited success in the past decade
due to off-flavor and the requirement for
sufficient toxicology testing.
1989, 36 countries approved the marketing
of irradiation foods.
The use of irradiation on medical products is
increasing; economic and reliable sterilizing
agent.
Irradiation is a lethal agent against
microorganisms.
Comparison of radiation
sensitivity of different
organisms
STERILIZATION OF MICROORGANISMS
LETHAL TO
INSECTS
SPROUTING
INHIBITED
LETHAL
TO
HUMANS
Dose
(rad)
NO ACUTE
EFFECTS
1
10
102
103
104
105
106
107
DESCRIPTION OF
RADIATION ENERGY
Radiation can be clasified in two groups: 1)
electromagnetic and 2) particle radiation.
Electromagnetic radiation:
 Various types of ionizing radiation in the
electromagnetic spectrum produce bacterial effects
by transfering the energy of photon into
characteristic ionizations in or near a biological
target.
 In addition to creating pairs of positive and
negative electron, ion can also produce free radicals
and activated moleculs, without any appreciable
rise in temperature (“cold sterilization”)
 Suggested irradiation: microwave, ultraviolet
gamma, x rays, and electrons.

DESCRIPTION OF
RADIATION ENERGY
Electromagnetic radiation:
 The lethal action of microwave is due to a thermal effect.
 X radiation and Gamma radiation; identical in nature but have
different origins.
Particle Radiation:
 The particles ussualy considered of importance in radiation biology
are alpha and beta neutron, meson, positron and neutrino.
 The currently applicable particles to sterilization is Beta particle or
electron.
 Alpha particles have limited penetrating ability
 Neutrons: is unacceptable since induces radioactivity
 Mesons and protons are produced only by expensive, high energy
machines.
LETHAL EFFECTS OF IRRADIATION ON
MICROORGANISMS
Intercellular effects
 Lesion caused by the direct action of ionizing irradiation on a
target molecules are the result of energy being transferred
within the target molecule itself
 Indirect action due to diffusion of radicals produced in the
adjacent volume.
 Indirect effects, in a sense, are still with in an organism, but
inactive the organism by diffusion to, and by reacting with, a
sensitive target site.
 An environmental effect caused by radicals and other
radiation-produced compounds form extracellularly and still
can be lethal to a cell.
 Some of this compuds, hydrogen and organic peroxides dan
radicals --------postirradiation effects.
LETHAL EFFECTS OF IRRADIATION ON
MICROORGANISMS
Intercellular effects
 Ionizing radiations can cause a wide variety
of physical and biochemical effects in
microorganisms.
 The primary cellular target that governs the
lost of viability is the DNA molecule of the
cell related to the chromosome volume.
 The larger volume, the more sensitive the
biologic unit was to ionizing radiation.
LETHAL EFFECTS OF IRRADIATION ON
MICROORGANISMS
Environmental effects


One may consider those lethal effects that originate
in the menstruum as a type of indirect effect.
The influence of the menstruum can be altered by:
1) using dried preparations in order to restrict the
moisture content only to that closely associated
with the cell, 2) freezing the menstruum and cells
to minimize the migration of free radicals, 3)
varying the temperature during irradiation and 4)
varying the concentration of the solute or organic
material under consideration.
LETHAL EFFECTS OF IRRADIATION ON
MICROORGANISMS

To decrease or eliminate the microbial population from a
surface or within a material by ionizing radiation involves
additional considerations.
– The microbial contaminants will consist of mixed microflora,
distributed in a manner characteristic of the material.
– Microorganisms growing as a dense mass in restricted area, or
diffuse when dispersed in aliquid, will be destroyed at different
rates.
– The physiological state of the organism will vary, and the
composition of the menstruum surrounding the microorganism
may also vary from that of an inert substance to a plant and
animal tissue of high complexity.
APPLICATION OF IONIZING RADIATION FOR
DESTRUCTION OF MICROORGANISMS
Two approaches:
– Partial or selective destruction (radiation pasteurization)
– Complete destruction (radiation sterilization)
Radiation Sterilization of food
 If the intent is to produce a sterile food product, certain conditions
must be met.
– For maximal shelf life stability, not only microorganisms but
tissue enzymes should be inactivated
– The food should be capable of possessing a long storage life
without needing refrigeration.
– Enzyme require a higher irradiation dosage for inactivation
than microorganisms; therefore, a sub sterilization thermal
treatment may be required to supplement radiation.
– The radiation tolerance of a material should be considered.
– The material will act as a shield, will also dter the extent of the
penetration of beta and alpha rays.
APPLICATION OF IONIZING RADIATION
FOR DESTRUCTION OF
MICROORGANISMS
Radiation Pasteurization of food



the dose employed are considerably
lower for pasteurization.
Less off-flavor development
The most numerous organisms
decreased, and the spoilage pattern, it
is expected, altered and inhibited.
APPLICATION OF IONIZING RADIATION
FOR DESTRUCTION OF
MICROORGANISMS
Radiation Pasteurization of food
 Radiopasteurization can be extend the shelf life of a
variety of fresh food products if certain factors are
considered.
1. the initial number of microorganisms must be reasonably low.
2. the irradiated product should be maintained at a refrigeration
temperature as low as possible.
3. the packaging must be the proper type
4. recontamination after irradiation must be minimal
5. the dosage should be low enough to preserve the characteristic
odor and flavor of the fresh product,
Note: it must be realized that not all foods, e.g. vegetables and
dairy products can tolerate radiation energy without undergoing
significant changes in such aspects as flavor and texture.
CHEMICAL EFFECTS OF
IONIZING RADIATIONS


Capable initiating a vast array of chemical
changes; gaseous, liquid and solid system
Ionizing radiation split or “radiolyze “ water.
Since many biological systems as well as
most foods are aqueous systems, this effect
on water is of key importance.
–
–
–
–
Excited water
(H2O)*
Free radicals
OH* and H*
Ionized water molecules (H2O)+
Hydrated electron
e-aq
CHEMICAL EFFECTS OF
IONIZING RADIATIONS

The species then react among themselves
or with other components of the system. In
pure water and in the presence of air they
produce in particular the following:
–
–
–
–
–
Hydrogen gas:
H2
Hydrogen peroxide: H2O2
Water:
H2O
Hydronium ion H3O+
Hydroxyde ion OH-