3 BEST METHODS OF PRESERVATION | Principles of Preservation



in this article, we are going to learn about preservation, the need of preservation, the aim of preservation, principles of preservation and the methods of preservation.


  • Preservation means just protecting the foods against spoilage, but scientifically it may be defined as a science that deals with the process for prevention of decay or spoilage of the food is called preservation.
  • In other words, just controlling the physical, chemical or microbial changes in the foods is called preservation.

1. Physical Changes: Colour, flavour, texture and taste etc.
2. Chemical Changes: Carbohydrate, fats, proteins, vitamins and minerals.
3. Microbial Changes: Mould, yeasts and bacteria


1. To supply to increase the shelf life of the food for increasing the supply.
2. To make the seasonal fruits available throughout the year.
3. To add variety to the diet.
4. To save time by reducing preparation, time and energy by fire.
5. To stabilize the prices of the food in the market.
6. To improve the health of the population.


Based on the perishability and the extent of preservation required, foods may be classified as:

  • Perishable foods: Those that deteriorate readily (fruits and vegetables) unless special methods of preservation are employed.
  • Semi-perishable foods: Those that contain natural inhibitors of spoilage (root vegetables) or those that have received some type of mild treatment which creates greater tolerance to the environmental conditions and abuses during distribution and handling (such as pickled vegetables).
  • Non-perishable foods (shelf-stable): Those that are non-perishable at room temperature (cereal grains, sugar, nuts). Some have been made shelf-stable by suitable means (canning) or processed to reduce their moisture content (raisins). Food preservation in the broad sense refers to all the measures taken against any kind of spoilage in food.


Sr NO. Name Of Crop Value Added Products
1 Apple Jam, juice, apple cider, canned apple, frozen apple, apple sauce etc.
2 Grapes Wine, resins, juice, syrup, jam etc.
3 Mango Juice, leather, dried mango, pickle, powder, jam, nectar, RTS, Panna etc.
4 Citrus Fruits Juice, squash, cordial, marmalade, jelly, pickle, powder etc.
5 Pineapple Jam, juice, nectar, RTS, powder etc.
6 Guava Jelly, jam, juice, nectar, RTS, etc.
7 Banana Banana powder, flour, chips, puree, jam, jelly, vinegar etc.
8 Anola Juice, toffees, candy, murabba, pickle etc.
9 Papaya Jam, tutty fruity etc.
10 Tomato Pulp, puree, paste, ketchup, sauce, soup powder, flakes, dehydrated tomatoes etc.
11 Chilli Pickle, sauce, chutney, etc.
12 Carrot Juice, powder, flakes, canned carrot, soup , fabricated baby foods, etc.
13 Ginger Paste, candy, preserve, pickle, RTS, juice, powder etc.
14 Leafy Vegetables Dried vegetables


There are three main principles of preservation:-

A. Prevention / delay the microbial decomposition of the food.
B. Prevention/delay the shelf decomposition of the food.
C. Prevention of damage by insects, animals, mechanical causes etc.

A. Prevention / delay the microbial decomposition of the food.

  • By Keeping out the micro-organisms: Asepsis
  • By Removal of micro-organisms: Filtration
  • By Hindering the growth and activity of micro-organisms: Anaerobic condition
  • By Killing the micro-organisms: Exposing at high temperature

1. Asepsis: It means preventing the entry of micro-organisms by maintaining general cleanliness while picking, grading, packing and transporting of fruits and vegetables, increasing their keeping quality and the product prepared from them will be superior quality.

2. Filtration: Fruits juice, beer, soft drinks, wines etc. enter through bacteria proof filters which are made of Asbestos pad or unglazed porcelain type of materials. These filters contain micro-organisms and allow the water or juice to percolate though with or without pressure.

3. Anaerobic conditions: It can be maintained by:

(i) Replacing the O2 by CO2 (carbonation)
(ii) Evacuating the sealed container (fruit juice)
(iii) Use of oils from top of the food (pickles)

4. Exposing at high temperature: Fruits can be exposed by high temperature such as:

(i) Canning: Food is exposed to a high temperature (> 1000 C) which prevents spoilage and inactivate the enzyme present in the food.
(ii) Irradiation: In the case of irradiation, the food is exposed to the radiations to kill the surviving micro-organism by ionizing and non-ionizing radiation like α, β and γ rays. Her, food is exposed to electromagnetic or ionizing radiation or various frequencies ranging from low-frequency electromagnet to high frequency i.e. gamma rays which destroy the micro-organism present in the food.

B. Prevention/delay the shelf decomposition of the food.

(i) By destruction or inactivating the enzyme: Blanching.
(ii) Prevention / delay the non-enzymatic chemical reactions       : Anti-oxidant


1. It is a primary treatment that has to soften the tissues to facilitate packaging.
2. To preserve the original colour and flavour
3. To destroy the certain enzyme which are undesirable
4. Elimination of the air
5. Mostly for vegetables
6. Remove micro-organisms
7. Remove astringent taste and toxins

Anti-oxidant: Anti-oxidant is substances that are used to protect the food gamma deterioration caused by exposure to the air.

1. BHA – Butylactic Hydroxy Anisole
    BHT – Butylactic Hydroxy Toluene
2. Gellales: Animal fat, Vegetable oil
3. Tocopherols: Animal fat
4. Ascorbic acid: Fruit juices, Citrus oil, Wine, Bears etc.
5. Lactic acid: Processed fruits and vegetables, Canned fruits,
6. Phosphoric acid: Vegetable oils, Animal fat and cola drinks


A. Bacteriostatic methods:

In this method, the environmental conditions are changed to prevent the growth of micro-organisms, such conditions are called bacteriostatic. These are:

1. DRYING OF FOODS: Drying is just the removal of moisture from the food to a certain level at which micro-organisms cannot grow is called drying, it can be done by two methods:

(i) Application of heat:

  • Sun-drying: Sun drying is the method by which food is directly exposed to sunlight. It is generally done in places where plenty of sunshine is available for a long period e.g. Rajasthan. The dried product in this method is inferior in quality.
  • Mechanical drying: This is a method of drying where the application of heat is applied by a mechanical dryer under the controlled conditions of temperature, humidity and airflow.
  • Vacuum drying: The temperature of the food and the rate of water removal are controlled by regulating the degree of vacuum and intensity of heat input.
  • Freeze drying: In this method, the food is dried by the sublimation process, i.e., just converting the food into ice without passing through the liquid form of water by means of vacuum plus heat applied in the drying chamber. In this method, the product is first frozen then water is removed by vacuum and application of heat which occurs simultaneously in same chamber.

(ii) Binding the moisture in the food:

  • Use of Sugar: The use of a high concentration of sugar bind up the moisture and make the food have a certain level of moisture at which microorganisms are not able to grow.
  • Use of Salt: The concentration of salt causes high osmotic pressure and tie up the moisture which inhibits the growth of microorganisms. It dehydrates the food by drying out and tying up moisture as it dehydrates the cells of the microorganisms. Salt reduces the solubility of O2 in the food by reducing the moisture. It interferes with the action of proteolytic enzymes. The effectiveness of NaCl is varied with the concentration of salt and temperature.


Chemical preservatives are substances that are added to food just to retard, inhibit or arrest the activity of microorganisms such as fermentation, pacification and decomposition of the food. Chemical preservatives are of two types:

  • Class-1 preservatives: Common salt, sugar, dextrose, spices, vinegar, ascorbic acid
  • Class-2 preservatives: Benzoic acid and its salt, SO2 and the salts of sulphuric acid, nitrates, sorbic acid and its salts, propionic acid and its salts, lactic acid and its salts.
  • Among the class-2 preservatives, only two chemical preservatives are used in fruits and vegetable Preservation:
  • KMS:
  • It releases the SO2 and it is unstable.
  • It is used for fruit that has non-water solvent pigment (colourless).
  • It can not be used in naturally coloured juices such as phalsa, Jamun because they have the  Anthocyanin pigment.
  • It can not be used in the product which is packed in a container because it acts on the tin containers and oil, Hydrogen Sulphide (H2S) which has an unpleasant smell and also form a black compound with the base plate of containers.
  • Best to control moulds than bacteria.
  • 350 ppm KMS is mostly used in fruit juice products.
  •  Sodium Benzoate:
  • It is a salt of benzoic acid and soluble in water.
  • It delays the fermentation of the juices.
  • It is commonly used in products which are having natural colours such as anthocyanin pigment.
  • It is more effective against yeast.
  • 750 ppm Sodium benzoate is mostly used in fruit juices, squashes and cordials.


  • Food additives are substances or mixtures of substances other than basic foodstuffs, which are present in the foods as reagents of any aspects of production, processing, storage, packaging etc.
  • Food additives are
  • sugar
  • salt,
  • acids,
  • Spices.
  • In the case of sugar and salts, they exert osmotic pressure by water is diffuses from the product through a semi-permeable membrane until the concentration reached equilibrium. They kill the microorganisms or do not allow them to multiply.

(i) Sugar: The concentration of 68-70% is used for the preparation of jam, jelly, marmalades etc. sugar act as a preservative by osmosis and not as a true poison for microorganisms. It absorbs most of the available water, so little water is available for the growth of microorganisms.

(ii) Salt: The concentration of salt 15-20% is used for the preparation such as pickles. Salt inhibits enzymatic browning and discolouration and also acts as an anti-oxidant. It exerts its preservative action by:

  • Causing high osmotic pressure resulting in the plasmolysis of microbial cells.
  • Dehydrating food and microorganisms by tying up the moisture.
  • Ionizing yields the chloride ion which is harmful to microorganisms, and
  • Reducing the solubility of oxygen in water, sensitizing the cells against CO2.

(iii) Acids:

  • Many processed foods and beverages need the addition of acids to impart their characteristic flavour and taste in the final product because acids provide desired flavour and taste.
  • They adjust the sugar and acid ratio in the food.
  • Proper balance flavour of the food.
  • They are also playing a role in controlling the pectin-gel formation.
  • The main acids are as follow:
    1. Acetic acid (Vinegar): commonly used for pickles, chutney, sauce and ketchup, just to inhibit the growth of microorganisms.
    2. Citric acid (Lime juice): used for the preparation of jam, jelly, squash, nectar etc. just to increase the acidity.
    3. Lactic acid (Lactose): used for the formation of curd from milk, raw flavour, specific to pickles.

(iv) Spices :

  • Spices are plant products that are used in flavouring foods and beverages to enhance the food flavour, colour and palatability.
  • They act as antibacterial and antifungal activity.
  • They impart as a colour agent.

Low temperature retards the microbial growth and enzyme reaction because it retards the chemical reactions. This is not a permanent method because some microorganisms can also grow at low temperatures.

  • Cellar storage (Above 150C): These are the underground room where surplus food can be stored for some time, only root crops such as potatoes, onion can be stored for a limited period.
  • Refrigerated storage (0 to 50C): Fruits and vegetables can be stored for 2-7 days. Semi-perishable crops, such as potatoes, apples etc. can be stored, in the commercial cold storage with proper ventilation, automatic controlled temperature for one year.
  • Freezing storage (-18 to -400C): It ties up the moisture and increases the concentration of dissolved substances in the food. But, sometimes enzymes are active even below the 00C. In this case before freezing, ‘Blanching’ is necessary for vegetable freezing.


  • In this method, the food material is exposed to a higher temperature and high temperature helps to kill the microorganisms due to the coagulation of protein. It helps in the inactivation of enzymes. Here moist heat is more effective than dry heat. High temperature can be employed by the following methods:
  • Pasteurization: Below 1000C
  • Boiling/ Cooking: at 1000C
  • Canning: Above 1000C

1. Pasteurization: There are three methods of pasteurization:

1. Bottle or holding pasteurization: This method is commonly used for the preservation of fruit juices at home. The extracted juice is strained and filled in bottles, leaving sufficient headspace for the expansion of the juice during heating. The bottles are then sealed air-tight and pasteurized.

2. Overflow method: Juice is heated to a temperature of about 2.50C higher than the pasteurization temperature and then filled in hot sterilized bottles up to the brim, during
filling and sealing the temperature of juice should not fall below the pasteurization temperature.

3. Flash pasteurization: The juice is heated rapidly to a temperature of about 5.50C higher than the pasteurization temperature and kept at this temperature for about a minute. This method is commonly used for canning of natural orange juice, grape and apple juices.

2. Boiling/ Cooking: The primary objective of cooking is to produce palatable food. Cooking results in:

1. Destruction or reduction of microorganisms and inactivation of undesirable enzymes.
2. Destruction of potential hazards in the foods which are present naturally through micro-organisms.
3. Improvement of colour, flavour and texture of the food.
4. It improves the digestibility of food components.
5. Putting the temperature at about 1000C. By this method, food can be preserved for 10-24 hours at low temperatures.

3. Canning: Canning is done at or above 1000C. In the case of fruits that are acidic, they are canned at 1000C, while in the case of vegetables that are non-acidic, they are canned at above 1000C. Here, high temperature can be obtained by using steam pressure, time varies according to the type of food. Due to anaerobic conditions, any survivable organism will not grow.


Low acid foods 5.3 and above Peas, Corn, Lime beans, Meat, Fish, Poultry and Milk
Medium acid foods 5.3 – 4.5 Spinach, Asparagus, Beets and Pumpkin
Acid foods 4.5 – 3.7 Tomatoes, Pears and Pineapple, Sauce
High acid foods below 3.7 Berries and Sauer kraut, Pickle



  • Preservation by filtration: In this method, juices are clarified by settling or by using ordinary filters and then passed through special filters which are capable of retaining yeasts and bacteria. Various types of germ-proof filters are used for this purpose.
  • Preservation by carbonation: Carbonation is the process of dissolving sufficient CO2 in water or beverage so that the product when served gives off the gas as fine bubbles and has a characteristic taste, carbonation life of beverage. Fruit juice beverages are generally bottled with CO2 content varying from 1-8 g/lit though carbon should be avoided as it destroys the flavour of the juice. The keeping quality of carbonated fruit beverages is enhanced by adding about 0.005% sodium benzoate. The level of carbonation is required according to the type of fruit juice and type of flavour.
  • Preservation by fermentation: This is one of the oldest methods of preservation. By this method, the foods are preserved by the alcohol or organic acid formed by microbial action.
    The keeping quality of alcoholic beverages vinegars and fermented pickles depends on the presence of alcohol acetic acid and lactic acid respectively. Wines, beers, vinegar, fermented drinks, fermented pickles are prepared by these processes. Fermentation is carried out by using acetic acid, lactic acid and alcohol etc.
  • Preservation by Antibiotics: Certain metabolic products of micro-organisms which are found to have a germicidal effect
  • Nisin: is an antibiotic produced by Streptococcus lactis an organism found in milk, curd, cheese and other fermented milk products. It is non-toxic and is widely used in the food industry, especially for the preservation of acid foods. It is commonly used in the canning of mushroom tomatoes and milk products. Nisin suppresses the growth of spoilage organisms.
    Subtilin: an antibiotic obtained from Bacillus subtilis is used in the preservation of asparagus, corn and peas.
  • Pimaricin: an antifungal antibiotic used for treating fruits and fruit juices.
  • Preservation by irradiation: It is a process of preservation of food by exposing them to ionizing energy/radiation which kills most of the spoilage causing organism and also inactivates the enzymes responsible for browning etc.
  • This method prevents sprouting in storage conditions (onion, potato etc.).
  • The irradiation of food can be considered to be a method of “Cold sterilization”.
  • Irradiation measured in rads.



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