preservation by radiation

1. BANGARU KARTHIK
M.Sc Microbiology

2.  Improved method of food preservation
 Radiations of various frequencies ranging from
low frequency electrical current to high
frequency gamma rays are used in food
 UV radiation, ionizing radiation and
microwave heating are used

3.  Entire spectrum of radiation
was grouped into two
categories

4. 1.Low frequency , low wave length
low quantum energy radiation
ranges from radio waves to infrared
rays
2. High frequency, shorter wave length
radiation
Divided into two categories
1. Low frequency and lower-energy radiation. Eg: UV
2. Radiation of higher frequency, high energy content
Eg:- Ionizing radiation

5.  Widely used in food industry
 Radiation with wavelength near 260nm is
absorbed strongly by purines & pyramidines
 UV with 200nm is strongly absorbed by
oxygen, may result in production of ozone and
effective against microorganisms

6.  Quartz mercury
lamp, low pressure
mercury lamps are
usual source of UV
radiation in food
industry
 Emit radiation at
254nm
 Rays range from
rays in visible range
to erythemic range

7.  Time
 Intensity
 Penetration

8.  Longer the time of exposure more effective the
treatment

9.  Intensity depends upon
 power of the lamp
 Distance from lamp to object
 Kind and amount
 Interfering material in the path

10.  Depends on nature of the object or material
being irradiated
 Penetration is reduced by
 Clear water
 Dissolved mineral salts – especially iron
 Cloudiness
 Thin layer of fatty or greasy material

11.  No penetration – opaque material
 Lamps reduce the number of microorganisms
in the air surrounding the food

12.  Gazing at UV causes irritation of eyes with in
few minutes
 Longer exposure of skin results in erythema
and reddening

13.  Resistance in microbes vary with
 Phase of growth
 Physiological state of the cells
 Location of organism(air / media)

14.  Treatment of water used for beverages
 Treatment of knives for slicing bread
 Treatment of bread and cakes
 Packing of sliced bacon
 Sanitizing of eating utensils

15.  includes
 X- rays or gamma rays
 Cathode rays or beta
 Protons
 Neutrons
 Alpha particles
Neutrons result in residual
radioactivity in food
Have low
penetration power
So these are not used in
food preservation

16.  These are penetrating electromagnetic waves
which are produced by bombardment of heavy
metal target with cathode rays within in
evacuated tube
 They are not economical for industrial use

17.  Are like X-rays
 Emitted from by products of atomic fission
 Cobalt60 & cesium 137 have been used as
sources
 Used for commercial applications
 Have good penetration
 Have been reported to be effective up to 20cm
in most foods

18.  Beam of electrons emitted from radioactive
material
 Higher the charge of electrons deeper the
penetration

19.  Beam of electrons emitted from the cathode of
an evacuated tube
 Have poor penetration

20.  Bactericidal efficiency of a given dose of
irradiation depends on following factors
 Kind and species of organism
 Number of organisms originally present
 presence or absence of oxygen
 Physical state of the food
 Condition of organism
 Composition of food

21.  Approximate lethal dose varies with kind of
species and organisms
 Eg: humans - 0.0056-0.0075
 insects - .22- .93

22.  More the organisms less effective the dose

23.  Effect of free oxygen varies with the organism
 Ranges from no effect to sensitization of
organism

24.  Both temperature and moisture content varies
with type of organism

25.  Proteins, catalase and reducing substances will
be protective
 Compounds that combine with SH group
would harmful to microbes

26.  Age , temperature of growth, sporulation,
vegetative or spore may effect sensitivity

27.  IN MEATS
 pH of meat rises
 Glutathione destroys
 Increase in carbonyl compounds, hydrogen
sulphide, methyl mercaptan

28.  In fats:
 Destruction of natural oxidants
 Partial polymerization and increase in carbonyl
compounds

29.  In vitamins
 Most type of vitamin levels are reduced
ss
 Many of the food enzymes are reduced