2. INTRODUCTION
◦ Food preservation aims at preventing the microbial spoilage
of food products and the growth of the food borne pathogen.
◦ Thus , the 2 principal goals of food preservation methods
are-
1}Increasing the shelf life of the food.
2}Ensuring the safety for human consumption.
3. ◦ Foods are readily decomposed unless special methods are
use for their preservation.
◦ All the methods of food preservation are based on following
principles:-
1}prevention or removal of contamination.
2}inhibition of microbial growth and their metabolism.
3}dehydration
4}osmotic pressure treatment
5}chemical treatment
6}treatment by radiation
4. Various practices are used for food
preservation .
These practices can be summarized
as two ways:-
1}physical ways
2}chemical ways
6. Centrifugation
◦ This method is used in some liquid foods such as Milk , fruit juice
and syrup to remove suspended undesirable particles like dust ,
food particles etc.
◦ The process consists of exposing the food in thin layers to a high
centrifugal force.
◦ Although this process is not intended to remove micro-organisms
but spores , large bacterial rods , bacterial clamp , chains , yeasts
and molds can be removed because of their heavier mass.
◦ under high force 90 % microbial population can be removed and
further , pasteurization it can be preserve for many days –
months.
7. Temperature
◦ The effectiveness of low temperature specially freezing foods preservation
was probably recognized by our ancestors around 40,000 B.C as natural
freezing and thawing is used to preserve during very early stage of civilization.
◦ Generally in colder regions of the world food are still preserve in natural ice.
◦ Earlier days romans used to reduce the temperatures of foods , they used
iceblocks from frozen lakes were cut stored and used to preserve raw foods
like meats , milk , fish etc by lowering the temperature.
◦ By 1840 with the help of ammonia compressed refrigerator units iceblocks
were produced commercially and used for food preservation.
8. Objective of low temperature preservation:-
I. Prevent and reduce growth of micro-
organisms
II. reduces or prevents catalytic activity of
microbial enzymes.
III.Germination of spores is reduced.
9. ◦ Foods are not preserved at low temperatures in order to kill
microbial cells.
◦ It is only used to preserve the foods by reducing the growth
of micro-organisms.
◦ Modern refrigeration and freezing has made it possible to
transport and store perishable foods for long periods of time.
◦ It increased the variety of food available.
◦ Low temperature preservation includes 2 different methods
◦ 1}chilling 2}freezing
10. CHILLING
◦ It involves preservation of foods like meat , eggs , fish ,
vegetables etc.
◦ Only for a few days at a temperature between 4degree
celcius – 7 degree celcius.
◦ If foods are kept for longer periods undesirable changes due
to active enzymes and psychrophilic micro-organisms such
Pseudomonas fluorescence & some Micrococcus spp takes
place causing spoilage.
11.
12. FREEZING
◦ This process is used for preserving perishible plant and
animal products for long periods from weeks to months.
◦ Before freezing the foods are stored , trimmed , washed and
blanched .
◦ Blanching consists of immersing the food in boiling water or
exposing it to live steam for a few minutes because blanching
destroys most of the micro-organisms and inactivate
enzymes i.e would alter the product even at low temperature.
◦ The food is then immediately packed and frozen.
13. ◦ In freezing technique quick freezing is preferred as compared to
slow freezing because quick freezing produces smaller ice
crystals and less damage to food tissues but slow freezing
produce large crystals of ice which rupture cell structure and
cause extensive drip or less of fluid upon thawing .
◦ As we know freezing cannot kill all micro-organisms the number
and types of viable and non-viable micro-organisms present in
frozen foods reflect the degree of contamination of raw product ,
the sanitation in processing .The microbial count of frozen foods
decreases during storage but many micro-organisms survive for
long periods i.e the reasons frozen food should be immediately
used after being Defroze because the micro-organisms begin to
multiply.
◦ Frozen foods does not loose nutritional value but flavour and
aroma is lost of fresh foods.
14.
15. IRRADIATION
◦ In the electro –magnetic spectrum , energy exists as waves
and the intensity of the energy increases as the waves get
shorter.
◦ Visible rays (400-800 nm) and they are of 2 types
1)invisible long waves like (>800 nm )ex-IR & radio waves.
2)Invisible short waves like (<300 nm )ex-UV rays, x-rays ,
cosmic rays
• Exposure to long waves , visible light waves and uv rays
does not cause any change in the atomic structures.
16. ◦Mostly exposure to X-rays , B-rays and other
types of rays can remove electron from the
outer shell of an atom and thus, form an ion
pair(+vely charged & -vely charged).
◦Ion formation or ionization does not make an
atom radioactive, so to induce radioactivity
the nucleus of an atom has to be disrupted
by much higher energies such as neutrons
like X-rays , B –rays and G-rays does not
have that much energy .
17. ◦ For application in food preservation , x-rays , b-rays and g –rays
were studied to penetrate inside foods and kill micro-organisms as
well as their efficiency and their effect on food quality :-
I. B-rays have very little penetration power they cannot penetrate
inside metal cans and are thought to be ineffective in food
preservation.
II. X-rays have good penetration power but cannot effectively
focused on food because of low efficiency it is not considered
favourably for food application in food.
III. G-rays have high penetration power and may be considered
effective and economical for use in foods.
18. COBALT-60(60Co)
◦ Cobalt-60 (60Co) and cesium-137 (137Cs) are considered to be
good source of g-rays.
◦ It is artificially induced radioactive isotope is produced for use in
nuclear medicine when its energy level becomes low and it cannot
be further used in medicine it is then used to irradiate foods.
◦ Because cobalt-60 is easily available over cesium-137 it is prefer
for food irradiation .
◦ Thus , foods irradiated with cobalt-60 do not become radioactive
instead the atoms in a food and in microbial cells form ion pairs
and other components that inhibit the multiplication of micro-
organisms.
19. DOSES
◦ Radiation dose was originally designated as (rad).
◦ 1 rad is defined as the quantity of ionizing radiation that
results in the absorption of 100 ergs of energy per gram of an
irradiated material.
◦ Current unit is gray (Gy)and 1 Gy =100 rad.
◦ When 1 kg of food absorbs the energy of 1 joule it has
received a dose of 100 rad.
◦ According to international health and safety authorities foods
irradiated upto 10,000 Gy are safe .
20. ◦ So , the dose levels for insects and different micro-organisms
are –
◦ Insects (</=1Gy)
◦ Molds , yeasts , bacterial cells – (0.5-10Gy).
◦ Bacterial spores –(10-50Gy).
◦ viruses-(10-200Gy)
◦ At present low dose level is used to control insects in fruits
and grains, parasites in meats and fish .
◦ Medium doses (1-10Gy) is used to control food borne
pathogens and spoilage micro-organisms to extend safety
and stability of refrigefrated foods.
◦ High doses to destroy spores and viruses.
21. Methods used:-
◦ Gamma rays & high-energy electron beams:-
◦ It has been used for preservation of fresh perishable canned
and packaged foods.
◦ They have good penetration and are effective to depth of 15
min most foods.
◦ Also known as (cold sterilization) as it produces only a few
degree rise in temperature of the product.
22. ◦ Ultraviolet rays:-they are short waves and are used to sterilize the
surface of foods.
◦ these rays have been successfully used for
1. the treatment of water for bevarages.
2. aging meats
3. Packaging of sliced bacon
4. Treatment of slicing bread
5. Utensils used for food processing
6. For prevention and spoilage by micro-organisms on the surface
of preserved pickles , cheese and prevention of air
contamination.
• Cold storage rooms of meat –processing plants are equipped with
UV lamps reduce the surface contamination and permit longer
periods spoilage –free storage.
23. ◦ Radurization / radiation pasteurization:-it kills over 98% but not 100% of
the micro-organisms by intermediate dose of radiation.
◦ This method increases the storage life of some meats , sea-
foods , certain fruits and vegetables when stored at low
temperature.
◦ Uses mild ionizing radiation dose less than (10Gy).
◦ The process intended to sterilize foods by destroying or
inactivating micro-organisms.
◦ The major risks are damage or loss of vitamins and proteins
and production of cancerogenic reactive radicals.
24. DRYING/DEHYDRATION
◦ The ability of dried seeds, grains , tubers and fruits to resist
spoilage was recognized by humans before the discovery of
agriculture.
◦ This method was practice to preserve large volume of food
produced during growing seasons to make them available
during non-growing season.
◦ Later, it was also used to preserve meat , fish , milk , not only
by removing water by drying but also by adding solutes in
food like salt , honey and starch to bind water.
25. ◦ It is not only preserve foods and stabilize the food supply but also to
develop different types of shelf-stable foods like
26. ◦In addition to that the relationship and influence of
moisture on microbial growth has been instrumental
is producing many types of intermediate moisture
ready to eat food because of their convinience these
foods are popular and the trend shows that the
popularity will continue .
◦The main objective of dehydration is to prevent or
reduce the growth of vegetative cells and germination
and outgrowth of spores of micro-organisms.
27. methods
◦ The water activity of foods can be reduced by using one or more of these 3
basic principles-
I. Removing water by dehydration .
II. Removing water by crystallization
III. Adding solutes to bind water
• Some of these methods and their effect on micro-organisms are briefly
described –
I. Natural dehydration
II. Freeze-drying
III. Smoking
IV. Foam-drying
V. Mechanical drying
VI. Intermediate moisture foods
28. Natural Dehydration
◦ it is a low cost method in which water is removed by heat of
sun.
◦ It is used to dry grains as well as dry fruits (raisins),
vegetables , fish , meat , milk & curd specially in warmer
countries.
◦ The process is slow , depending on the conditions used
spoilage and pathogenic bacteria as well as yeasts and
molds can grow during drying .
29. Mechanical drying
◦ It is controlled process and drying is achieved in few seconds to
few hours.
I. Tunnel drying in which food travels through a tunnel against
flow of hot air that removes the water.
II. Roller drying in which a liquid is dried by applying a thin layer
on the surface of a roller drum heated from inside.
III. Spray drying in which liquid is sprayed in small droplets which
then come in contact with hot air that dries the droplets
instantly.
Liquids may be partially conc.before drying by evaporation ,
reverse osmosis , freeze concentration.
30.
31. Freeze drying
◦ It is costly process use for both liquid and solid foods.
◦ The process initially involves freezing the food , rapidly at a
low temperature and then expose the frozen food to a high
vaccum environment.
◦ Water molecules are removed without affecting the shape.
32.
33. Foam drying
◦ in this method a product is whipped to produce stable foam
to increase the surface area.
◦ The foam is then dried by warm air .
34. Smoking
◦ many meat and fish products are exposed to low heat and
smoke for cooking and depositing smoke on the surface at
same time.
◦ The heating process removes water from the products.
35. Intermediate moisture foods(IMF)
◦ They can be eaten without rehydration but are shelf stable for
long period without refrigeration.
◦ Yeast and mold grown in some food is inhibited by specific
preservatives such as sorbate and propionate .
◦ Some examples of these are
