TOPIC 2

FOOD
PRESERVATION
 WHAT IS FOOD PRESERVATION?
“Food preservation is the technique to prevent food spoilage, food poisoning, and microbial contamination in
food.”
 Food preservation is one of the methods to protect food from unwanted microbial growth.
After the food is produced, the food will be stored and protected by covering the rice and curry with lids to
keep away flies and other insects. By this, we are protecting it from any infection caused by them. This is a
short-term condition.
Food preservation, on the other hand, is done to preserve food for a longer time.

 Objectives of Food Preservation

Following are the important objectives of food preservation:
1. To prevent microbial contamination.
2. To kill pathogens.
3. To minimise food spoilage and food poisoning.
 Food Preservation Methods
 Food preservation started long back in ancient times.
 Cooling, freezing, fermentation, sun-drying, etc., are few age-old food preservation
techniques.
 Chemicals and other natural substances were used for preservation. These substances
are known as preservatives. Let us discuss some of the methods of preservation in
detail.
 Chemical Method
Salt and edible oils are two main preservatives which are used since ages to
prevent microbial growth. This is why we add extra oil to pickles. Preservation by
salt is known as salting. Salting helps to preserve fruits for a long term. Meats and
fishes can also be preserved by salting.
Other synthetic preservatives include vinegar, sodium benzoate, sodium
metabisulphite, etc.
Sugar
Sugar is another common preservative used in jams and jellies. Sugar is a good
moisture absorbent. By reducing moisture content, it restrains the microbial
growth.
 Heat and Cold Methods
 Boiling and refrigeration prevent around 70 percent of microbial growth. Boiling
kills the microorganisms that cannot tolerate extreme temperatures. Thus, it
helps in food preservation.
 Refrigerators have very low temperatures. Since microbes do not get optimum
temperature they need for growth, their growth is inhibited. Pasteurization
developed by Louis Pasteur is used until today to preserve milk.
 Smoking
 Smoking prevents dehydration in fish and meat and thus prevents spoilage. The
wood smoke contains a large number of anti-microbial compounds that slow
the rancidification of animal fats.
 TYPE OF PRESERVATION / PRESERVATION TECHNIQUE

Canning
 The food contents are sealed in an airtight container at high temperatures. Meat, fish,
fruits are preserved by canning.
Sterilization
 This method is carried out to remove microbes from food. For eg., milk sterilization at
100°C kills the microbes.
Dehydration
 It is the process of removal of water from food. It is the simplest method and prevents
food spoilage by removing water.
Lyophilization
 This is the process of freezing and dehydration of the frozen product under vacuum.
Radiation
 This method is also known as cold sterilization.
 The UV rays, X rays, gamma rays kill all the unwanted microbes present in food.
 Irradiation
 Some fruits can be subjected to ionizing radiation to destroy parasites, insects and
bacteria.
 The treatment also slows ripening without a noticeable effect on the fruits’ flavor and
texture.
 Irradiated fruits must be labeled“treated with radiation,” “treated by irradiation”

Irradiation Symbol
Acidulation
Apples, pears, bananas, peaches and other fruits turn brown when cut. Although this
browning is commonly attributed to exposure to oxygen, it is actually caused by the
reaction of enzymes.
Enzymatic browning can be retarded by immersing cut fruits in an
acidic solution such as lemon or orange juice. This simple technique is referred to as
acidulation.
Soaking fruits in water or lemon juice and water (called acidulated water)
is not recommended.
Insufficient amount of salt or sugar is added to the water,
the fruits become mushy and;
if enough salt or sugar is added to retain texture, the flavor
is affected.
Freezing
 Freezing is a highly effective method for preserving fruits. It severely inhibits the
growth of microorganisms that cause fruits to spoil.
 Freezing does not destroy nutrients, although the appearance or texture of most fruits
can be affected because of their high-water content.
 This occurs when ice crystals formed from the water in the cells burst the cells’ walls.
 Many fruits, especially berries and apple and pear slices, are now individually quick
frozen (IQF).
 This method (IQF) employs blasts of cold air, refrigerated plates, liquid nitrogen,
liquid air or other techniques to chill the produce quickly.
 Speeding the freezing process greatly reduces the formation of ice crystals.
 Drying
 Drying is the oldest known technique for preserving fruits, having been used for more than 5000
years. When ripe fruits are dried, they lose most of their moisture.
 This concentrates their flavors and sugars and dramatically extends shelf life. Although most fruits
can be dried, plums (prunes), grapes (raisins, sultanas and currants), apricots and figs are the
most commonly dried fruits.
 The drying method can be as simple as leaving ripe fruits in the sun to dry naturally or the more
cost-efficient technique of passing fruits through a compartment of hot, dry air to quickly extract
moisture.
 Dried fruits actually retain from 16 to 26 percent residual moisture, which leaves them moist and
soft. They are often treated with sulfur dioxide to prevent browning (oxidation) and to extend
shelf life.
 Dried fruits may be eaten out of hand; added to cereals or salads; baked in muffins, breads, pies
or tarts; stewed for chutneys or compotes; or used as a stuffing for roasted meats or poultry.
 Before use, dried fruits may be softened by steeping them for a short time in a hot liquid such as
water, wine, rum, brandy or other liquor.
 Storage : dried fruits in airtight containers to prevent further moisture loss; keep in a dry, cool
area away from sunlight. Dried fruits may mold if exposed to both air and high humidity.
 BRINE
A method involving the soaking of food in a liquid solution consisting of water, salt, sugar,
and possibly herbs and spices in order to preserve, tenderize or flavor various food and
cuts of foods.
Similar to osmosis process.
Foods placed in brines as a means to cure or pickle the foods are brined in order to extend
the shelf life of an item, such as meat, fish and vegetables.
For foods brined to enhance flavors and moisture content, brining is a process that is
undertaken to add moisture to the muscle fibers within the food and to assist with
dissolving proteins in the fibers so they become liquid instead of solid in mass.
As the food soaks, the salt, which may also contain seasonings and spices, penetrates into
the meat fibers. This allows any flavored seasonings or spices placed in the liquid brine to
be drawn in as well, thus enhancing the quality of the food being brined. A brining spice
that is often added to a brine may consist of a variety of seasonings such as coarse or
flaked salt (sea salt and kosher salt are common), pepper or peppercorns, sage, allspice,
thyme, galic, cardamom, lavender, juniper, citrus zest, and other selected ingredients.
 CURING
“Curing with salt and sugar may be called salting, salt-curing, sugar-curing or honey-curing. The
application of pellets of salt, called corns, is often called corning. Curing in a water solution or brine is
called wet-curing or pickling or brining. Paul Bertolli notes that a pickle contains nitrite in addition to
salt. (Bertolli 2003) The curing of fish is sometimes called kippering.”
Curing also refers to various preservation and flavoring processes, especially of meat or fish, by the
addition of a combination of salt, sugar and either nitrate or nitrite. Many curing processes also
involve smoking. The etymology of the term is unclear, but it is thought to derive from the same
Latin cura, -ae, from which the other English meanings are also derived.
 Chemical action of curing
Salt inhibits the growth of spoilage-causing microorganisms by drawing water out of microbial cells
through osmosis. As the unwanted bacterial population decreases, other beneficial bacteria,
primarily of the Lactobacillus genus, come to the fore and generate an acidic environment (around
4.5 pH).
The sugar included in the cure is used as food by the lactobacilli; generally dextrose is preferred over
sucrose, or table sugar, because it seems to be more thoroughly consumed by the bacteria. This
process is in fact a form of fermentation, and, in addition to reducing further the ability of the
spoilage bacteria to grow, accounts for the tangy flavor of some cured products. Concentrations of
salt up to 20% are required to kill most species of unwanted bacteria
 PICKLING
“Pickling is the process of preserving or extending the shelf life of food by either anaerobic
fermentation in brine or immersion in vinegar. The pickling procedure typically affects the
food's texture and flavor. The resulting food is called a pickle, or, to prevent ambiguity,
prefaced with pickled.”
Pickling also using an acidic brine to preserve a food. Acidic brines are made with either
salty water, sugar water, lemon juice, or vinegar. Either substance (or sometimes a
combination of them) is poured over vegetables, fruit, meat or fish which are then placed
in a tight jar for a few days.