BANGARU KARTHIKM.Sc Microbiology

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

Entire spectrum of radiation was grouped into two categories

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

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

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

Time

Intensity

Penetration

Longer the time of exposure more effective the treatment

Intensity depends upon

power of the lamp

Distance from lamp to object

Kind and amount

Interfering material in the path

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

No penetration – opaque material

Lamps reduce the number of microorganisms in the air surrounding the food

Gazing at UV causes irritation of eyes with in few minutes

Longer exposure of skin results in erythema and reddening

Resistance in microbes vary with

Phase of growth

Physiological state of the cells

Location of organism(air / media)

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

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

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

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

Beam of electrons emitted from radioactive material

Higher the charge of electrons deeper the penetration

Beam of electrons emitted from the cathode of an evacuated tube

Have poor penetration

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

Approximate lethal dose varies with kind of species and organisms

Eg: humans - 0.0056-0.0075 insects - .22- .93

More the organisms less effective the dose

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

organism

Both temperature and moisture content varies with type of organism

Proteins, catalase and reducing substances will be protective

Compounds that combine with SH group would harmful to microbes

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

IN MEATS pH of meat rises Glutathione destroys Increase in carbonyl compounds, hydrogen

sulphide, methyl mercaptan

In fats: Destruction of natural oxidants Partial polymerization and increase in carbonyl

compounds

In vitamins Most type of vitamin levels are reduced

ss Many of the food enzymes are reduced