Food preservation, principles, preservation technique, importance of food preservation.

1. Food preservation
Md . Sajib Al Reza
Lecturer
Nutrition And Dietetics
College Of Nursing Science Dinajpur
Dinajpur, Bangladesh
Email: Sajib.Ftns2010@gmail.Com

2. Food preservation… …
• Food Preservation: The term food preservation refers to any one of
a number of techniques used to prevent food from spoiling. It
includes methods such as canning, pickling, drying and freeze-
drying, irradiation, pasteurization , sterilization, curing, pickling,
irradiation, chilling, refrigeration, dehydration, smoking, and the
addition of chemical additives.
• Food preservation is to prevent the growth of microorganisms as
well as slowing the oxidation of fats that cause rancidity.
• Food preservation is known “as the science which deals with the
process of prevention of decay or spoilage of food thus allowing it
to be stored in a fit condition for future use”. Preservation ensures
that the quality, edibility and the nutritive value of the food
remains intact.

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Preservation involves –
 preventing the growth of bacteria, fungi and other microorganisms,
 as well as retarding oxidation of fats to reduce rancidity.
Basically food preservation ensures that food remains in a state where it is
• not contaminated by pathogenic organisms or chemicals
• does not lose optimum qualities of colour, texture, flavor and nutritive
value
• Stop oxidation that causes the destruction of essential biochemical
compounds and/or the destruction of plant and animal cells.
The various food preserving methods are all designed to reduce or
eliminate one or the other (or both) of these causative agents.

4. Principles of food preservation … …
Principles of food preservation:
(A) Prevention or delay of the growth of micro-organisms
(i) Avoiding invasion of micro-organisms e.g. by aseptic techniques
(ii) Removing micro-organisms e.g. filtration
(iii) Inhibiting the growth and activity of micro-organisms e.g. freezing, refrigeration, drying,
anaerobic conditions, chemicals or antibiotics
(iv) Killing the micro-organisms e.g. heat or irradiation
(B) Prevention or delay of self-decomposition
(i) Destruction or inactivation of inherent enzymes naturally existing in food e.g. by blanching
(ii) Prevention or delay of chemical reactions e.g. prevention of oxidation by using
antioxidants

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(C) Prevention of damage from insects or animals
(i) By using suitable chemicals to kill insects or animals from destroying the foods.
(ii) By storing foods in dry, air tight containers to prevent the insects or animals from
destroying them.

6. Various methods of food preservation … …

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• Drying: Food drying is a method of food preservation in which food is dried
(dehydrated or desiccated) under sunshine or open air through the removal
of water to inhibits the growth of bacteria, yeasts, and mold. Meats, fish,
fruits, and vegetables, chilies, mangos are preserved by sun drying from
ancient time.
• Dehydration: Dehydration, usually describes the removal of moisture by
applying artificial heat current under controlled conditions.
Dehydration Drying
A faster process A slower process
Under controlled hygienic conditions Under open-air conditions with little
hygienic control
Not dependent on the weather Not possible in cloudy weather or
rainy days
Investment on machinery and
processing cost is needed
No machinery and processing cost is
needed

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• Cooking: Cooking or cookery is the art, technology and craft of preparing food for
consumption with or without the use of heat. Cooking methods include Roasting,
Baking, Boiling, Frying, Steaming, Smoking etc.
• Cellar storage: The temperature in cellar (underground rooms) is seldom lower
than 15oC. It is not enough to prevent the action of many spoilage organisms or of
plant enzymes. Root crops, potatoes, cabbage, apples, onions and similar foods can
be stored for limited periods.
• Refrigeration (or) chilling (0 to 5oC): Refrigeration at 5oC lowers the growth rate
of micro-organisms but does not stop microbial growth. Chilling temperature are
obtained and maintained by means of ice or mechanical refrigeration. It may be
used temporary preservation until some other preservative process is applied.
Most perishable foods, including eggs, dairy products, meats, sea foods, vegetables
and fruits, may be held in chilling storage for a limited time.

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• Freezing: For frozen food, it should be stored at or below -18 oC where the
enzymatic and microbial changes may be stopped or extremely slow. Frozen food (-
10 oC) usually does not have any free water (reduce Aw). Freezing may kill some
but not all microorganisms and slowing of oxidation reactions. Food should not be
refrozen after thawing.
• Smoking: Smoking is the process of flavoring, browning, cooking, or preserving
food by exposing it to smoke from burning or smoldering material, most often
wood. Meats and fish are the most common smoked foods. In cold smoking cold
smoking are typically done between 20 to 30 °C. Cold smoking does not cook foods
and foods take on a smoked flavor, but remain relatively moist. Hot smoking
occurs within the range of 52 to 80 °C. Within this temperature range, foods are
fully cooked, moist, and flavorful. Smoke roasting or "smoke baking" refers to any
process that has the attributes of smoking combined with either roasting or baking
above 82 °C.

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• Salting: Salting is the preservation of food with dry edible salt. It is related to
pickling, brining, and is one form of curing. Reduction in water activity sufficient to
delay or prevent microbial growth. salt solution (20-40%/100ml water) known as
brine. Salting is used because most bacteria, fungi and other potentially pathogenic
organisms cannot survive in a highly salty environment, due to the hypertonic
nature of salt. Any living cell in such an environment will become dehydrated
through osmosis and die or become temporarily inactivated. salt-cured foods are
salted fish, salt-cured meat, hams, bacon, Vegetables such as runner beans,
cucumbers and cabbage are preserved in this method.
• Pickling: Pickling is the process of preserving food by anaerobic fermentation in
brine or vinegar. The resulting food is called a pickle. 20% Vinegar or citric acid
lower the pH of 4.6 or lower and thus inhibit the growth of many micro-organisms.
Pickling can preserve perishable foods for months. Antimicrobial herbs and spices,
such as mustard seed, garlic, cinnamon or cloves, are often added. Foods that are
pickled include meats, fruits, eggs, and vegetables, jams, jellies and squashes,
pickles, sauces and chutney.

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• Jugging: Meat can be preserved by jugging. Jugging is the process of
stewing the meat (commonly game or fish) in a covered earthenware
jug or casserole. The animal to be jugged is usually cut into pieces,
placed into a tightly-sealed jug with brine or gravy, and stewed. Red
wine and/or the animal's own blood is sometimes added to the
cooking liquid.
• Sugar solution: Sugar binds moisture and thus can preserve food by
preventing the growth of microorganisms if a high concentration (65%
or above) is used. Sugar tends to draw water from the microbes
(plasmolysis). This process leaves the microbial cells dehydrated, thus
killing them. Products such as apples, pears, peaches, apricots, and
plums, jams and jellies are preserved by using sugar. Heating the fruit
with antimicrobial sugar syrup.

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• Chemical: An ideal preservative should meet the following criteria:
• (i) can inhibit the growth of a wide range of micro-organisms
• (ii) should be non-toxic to humans
• (iii) should not be expensive
• (iv) should not affect the flavour, taste or aroma of the food product
• (v) should not be inactivated by the food itself
• (vi) should not promote the development of resistant micro-organisms
• (vii) should kill rather than inhibit the micro-organisms
• Preservative food additives can be antimicrobial—which inhibit the growth of bacteria or
fungi, including mold—or antioxidant, such as oxygen absorbers, which inhibit the
oxidation of food constituents. Some familiar examples of food additives are sodium
benzoate and benzoic acid; calcium, sodium propionate, and propionic acid; calcium,
potassium, sodium sorbate, and sorbic acid; and sodium and potassium sulfite. Examples
of the latter class of additives include calcium, sodium ascorbate, and ascorbic acid (vitamin
C); butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT); lecithin; and
sodium and potassium sulfite and sulfur dioxide.

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• Irradiation: Food absorbs and is heated up by radiant energies. Radiant
energies can kill microorganisms without marked increase of temperature
as well as marked changes in the nature of food. Gamma rays, x-rays and
electromagnetic, ultra-violet radiations are commonly used for food
preservation. Irradiation can be used in a wide range of area in food
preservation:
• (i) Poultry products and seafood
• (ii) Fruits
• (iii) Prevention of sprouting in potatoes and onions
• (iv) Delaying ripening in fruits
• (v) Preservation of seafood
• (vi) Prevention of insect infestation in dry foods and food products
• Lye: Sodium hydroxide (lye) makes food too alkaline for bacterial growth.
Lye will saponify fats in the food, which will change its flavor and texture.
Ex: Olive recipes

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• Vacuum packing: Vacuum packing is a method of packaging that removes air
from the package prior to sealing. This method involves (manually or
automatically) placing items in a plastic film package, removing air from inside,
and sealing the package. Vacuum packing reduces atmospheric oxygen, limiting
the growth of aerobic bacteria or fungi. It is used to store cereals, nuts, cured meats,
cheese, smoked fish, coffee, and potato chips.
• Anaerobic condition/ Modified atmosphere: Anaerobic condition means a
condition lack of or containing only minimum amount of air or oxygen. It can
prevent the surviving bacteria in food from growing in the container. The container
is completely filled with food and air in unfilled space is removed or replaced by
nitrogen or carbon dioxide.
• Canning: Canning involves cooking food, sealing it in sterilized cans or jars, and
boiling the containers to kill or weaken any remaining bacteria and their spores as
well as inactivating enzymes as a form of sterilization in which over 100 C is used.
The packaging materials for canning can be tin or glass. The basic principle behind
canning is that a food is sterilized, usually by heating, and then placed within an
air-tight container. Example: meat, fruit, vegetables, and even milk.

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Pasteurisation (temperature below 100 C): Pasteurisation is a heat treatment that kills part
of the micro-organisms present in food using a temperature under 100 C. The temperature
used ranges from 65-75 C. There are two ways of pasteurisation:
❖ HTST (High temperature-short time)
• Food product is heated at high temperature for a short time. For example, milk is heated to 72
C and held for 15 seconds.
❖ LTLH (Low temperature-long time)
• Food product is heated at a lower temperature for longer period of time. For example, milk is
heated to 62.8 C and held for 30 minutes.
Boiling or heating at about 100 C: Most fruits and vegetables can be preserved for a longer
time by applying heat at about 100 C. Inherent enzymes which initiate self-decomposition can
be destroyed after boiling at 100 C. This process is called blanching.
Sterilization (temperature 100 C or above): It is a process that all micro-organisms are being
killed at high temperature or radiation. The time and temperature necessary for sterilization
vary with the type of food.

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• Fermentation: Fermentation in food processing is the process of converting
carbohydrates to alcohol or organic acids using microorganisms—yeasts or
bacteria—under anaerobic conditions. Fermentation usually implies that the action
of microorganisms is desired. similar processes take place in the leavening of bread
(CO2 produced by yeast activity), and in the preservation of sour foods with the
production of lactic acid, such as in sauerkraut and yogurt. Example: wine, beer,
and cider, cheese, vinegar, olives.
• Hurdle technology: Hurdle technology is a method of ensuring that pathogens in
food products can be eliminated or controlled by combining more than one
approach. These approaches can be thought of as "hurdles" the pathogen has to
overcome if it is to remain active in the food. The right combination of hurdles can
ensure all pathogens are eliminated or rendered harmless in the final product.

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• Baking: Baking is a method of cooking food that uses prolonged dry heat,
normally in an oven, but also in hot ashes, or on hot stones. Heat is gradually
transferred "from the surface of cakes, cookies, and breads to their centre. Bread,
cakes, pastries, puddings, vegetables and potatoes may be cooked by this method.
• Blancing: Food is dipped in boiling water for 5seconds to 2 minutes. blanching
involves pouring enough boiling water on the food to immerse for sometime in
boiling temperature, than immediately immerse in cold water. It inactivate and
destroy enzyme. It improves color and flavor of food.

20. Importance of Food Preservation …. ….
Food preservation helps in:
1. Increasing the self-life of foods thus increasing the supply. So many perishable
foods can be preserved for a long time.
2. Making the seasonal food available throughout the year.
3. Adding variety to the diet.
4. Saving time by reducing preparation time and energy, as the food has already
been partially processed.
5. Stabilising prices of food, as there is less scope of shortage of supply to demand.
6. Decreasing wastage of food by preventing decay or spoilage of food.
7. Improving the nutrition of the population. Preserved foods help people to bring a
variety in the diet, thereby decreasing nutritional inadequacies.

21. Thank you