preservation by radiation
TRANSCRIPT
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BANGARU KARTHIKM.Sc Microbiology
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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
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Entire spectrum of radiation was grouped into two categories
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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
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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
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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
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Time
Intensity
Penetration
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Longer the time of exposure more effective the treatment
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Intensity depends upon
power of the lamp
Distance from lamp to object
Kind and amount
Interfering material in the path
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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
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No penetration – opaque material
Lamps reduce the number of microorganisms in the air surrounding the food
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Gazing at UV causes irritation of eyes with in few minutes
Longer exposure of skin results in erythema and reddening
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Resistance in microbes vary with
Phase of growth
Physiological state of the cells
Location of organism(air / media)
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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
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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
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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
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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
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Beam of electrons emitted from radioactive material
Higher the charge of electrons deeper the penetration
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Beam of electrons emitted from the cathode of an evacuated tube
Have poor penetration
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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
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Approximate lethal dose varies with kind of species and organisms
Eg: humans - 0.0056-0.0075 insects - .22- .93
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More the organisms less effective the dose
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Effect of free oxygen varies with the organism Ranges from no effect to sensitization of
organism
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Both temperature and moisture content varies with type of organism
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Proteins, catalase and reducing substances will be protective
Compounds that combine with SH group would harmful to microbes
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Age , temperature of growth, sporulation, vegetative or spore may effect sensitivity
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IN MEATS pH of meat rises Glutathione destroys Increase in carbonyl compounds, hydrogen
sulphide, methyl mercaptan
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In fats: Destruction of natural oxidants Partial polymerization and increase in carbonyl
compounds
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In vitamins Most type of vitamin levels are reduced
ss Many of the food enzymes are reduced