Food Preservation

Food preservation involves the action taken to maintain foods with the desired properties or nature
for as long as possible.

Traditional Method for Food Preservation

1.COOKING

Cooking is a heating process, the primary object of which is to produce a more palatable food. The
word "cooking" is broad term embodying at least six form of heating including; baking, broiling
roasting, boiling, frying and stewing. The method of applying heat energy and the duration differ
somewhat for each of these processes. Baking, broiling and roasting usually required dry heat at
relatively high temperature greater than 100°C), boiling and stewing are done by placing the product
in boiling water and frying involves cooking oil and temperatures much greater than 100°C. Two
preservative changes occur in food as a result of cooking:

(i) destruction or reduction of microorganisms and

(ii) Inactivation of undesirable enzymes

(III) Destruction of potentially hazardous toxin present naturally or through micro

organisms

(IV) Alteration of color, flavor and texture and

(V) Improve digestibility of food.

Undesirable changes also may occur such as degradation of nutritive component

and sensory attributes. Principles which can be applied to describe the effect of cooking

on reduction of microorganisms and enzymes also can be applied to other changes

occurring during cooking.

2. BLANCHING

Blanching of fruits and vegetables is done by immersing them in hot/boiled water or

steam by exposing them to live steam or hot air for a proper period (2-5 min) of time

followed by cooling. The extent of blanching varies with food. Fruits are generally not

blanched leaving the oxidizing enzyme system active. Blanching is a thermal treatment to

be done prior to freezing, drying and canning for the following purposes:

(a) It inactivates most of the plant enzymes which cause harness, discoloration

(polyphenol oxidase), off flavor (peroxidase), softening and loss of nutritive value.

(b) The reduction of area of leafy vegetables and facilitate their easy handling.

(c) Removes tissue gases which reduce Sulphides.

(d) To destroy the microorganisms to about 99%.

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(f) To remove undesirable acids and astringent taste of the peel and spinach.

(g) Removes the skin of vegetables such as beetroot and tomatoes which helps in their

peeling.

Two of the most heat resistant and widely distributed enzymes in plant tissues are

peroxidase and catalase. Activity of these enzymes, therefore, can be used to evaluate

the effectiveness of a blanching treatment. The heating time necessary to destroy

catalase or peroxidase depends on the type of fruits and vegetables, the method of

heating medium, the size of the fruit and vegetables and the temperature of heating

medium. Heating media other than water (e.g. steam, hot air, and microwave) and at

temperatures other than 100°C can be used blanching time should not be more than 5

minutes.

3. PASTEURIZATION

The pasteurization is thermal process in which the harmful pathogen/ microorganism are

partially destroyed at predetermined time and temperatures. The high temperature and

short time (HTST) method involves a comparatively high temperature for a short time

(71.6°C for 15 second for milk), whereas the low temperature and long-time procedure

involves, relatively low temperature for longer time (e.g. 62.7°C for 30 minutes for milk).

Optimization process depends on the relative destruction rate of organisms as compared

to quality factors, but generally the HTST process results in maximum product quality. The

time temperature treatment used in pasteurization depends on:

(i) The heat resistance of the particular vegetative or pathogenic microorganism. The

process is designed to destroy, and

(ii) The sensitivity of product quality to heat.

4. STERILIZATION

Sterilization refers to complete destruction of microorganisms. Because of the resistance

of certain bacterial spores to heat, this frequently requires a treatment of at least 121°C

of wet heat for 15 min or its equivalent. It also means that every particle of the food must

receive this heat treatment.

If a can of food is to be sterilized, then immersing it at 121°C into pressure cooker or retort
for 15 min will not be sufficient because of the relatively slow rate of heat transfer through

the food into the can. Depending on the size of the can, effective time to achieve true

sterility may be several hours. During this time there can be many changes in the food

which reduce its quality. Fortunately, many foods need not be completely sterile to be

safe and have keeping quality.

5. CANNING AND BOTTLING

Canning process was first developed by Nicholas Appert in France in the year 1809.

Canning involves cooking fruits or vegetables, sealing them in sterile cans or jars, and

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boiling the containers to kill or weaken any remaining bacteria as a form of pasteurization.

Various foods have varying degrees of natural protection against spoilage and may

require that the final step occur in a pressure cooker. High-acid fruits like strawberries

require no preservatives to can and only a short boiling cycle, whereas marginal fruits

such as tomatoes require longer boiling and addition of other acidic elements. Many

vegetables require pressure canning. Food preserved by canning or bottling is at

immediate risk of spoilage once the can or bottle has been opened. Lack of quality control

in the canning process may allow ingress of water or micro-organisms. Most such failures

are rapidly detected as decomposition within the can causes gas production and the can

will swell or burst. However, there have been examples of poor manufacture and poor

hygiene allowing contamination of canned food by the obligate, Clostridium botulinum

which produces an acute toxin within the food leading to severe illness or death. This

organism produces no gas or obvious taste and remains undetected by taste or smell.

Food contaminated in this way has included Corned beef and Tuna.

6. DRYING

Drying is thermo-physical and physio-chemical operation by which the excess moisture

from a product is removed. It is defined as a process of moisture removal due to

simultaneous heat and mass transfer. Drying is the process of removal of moisture from

the agricultural product to a safe level for preservation of quality, quantity, nutritional

value and viability. It refers to removal of moisture from grains and other products to a

predetermined level, whereas dehydration means removal of moisture to very low levels

usually to bone dry condition. Drying makes the food grains and other product suitable
for safe storage and protects them against attack of insects, molds and other

microorganisms during storage.

Drying makes the food grains and other products suitable for safe

storage and protects them against attack of insects, molds and other micro-organisms

during storage During drying, the moisture from solid gets vaporized and diffused in dilute

environment. Removal of moisture takes place by high pressure or high temperature

conditions.

The main purpose of drying is to enhance storability and minimize packaging cost. The

quality of product and its cost are greatly influenced by the drying operation. The quality

of dried product is judged by the amount of physical and biochemical degradation which

occurs during dehydration process. The pretreatment, drying temperature, time and

moisture content influence the final product quality. Low temperatures generally have a

positive influence on the quality but require longer processing time. Low water activity

retards or eliminates the growth of microorganism and increase storability of food

products but result in higher lipid oxidation rates. Many fruits can be dried, for example,

the process is often applied to apples, pears, bananas, mangoes, papaya, apricot and

coconut. Zante currents, sultanas and raisins are all forms of dried grapes. Drying is also

the normal means of preservation for cereal grains such as wheat ,maize, oats ,barley,

rice, millet and rye.

DRYING METHODS:

The agricultural product drying methods can be broadly grouped into two,

(1) sun/solar drying,

(2) artificial drying with mechanical means.