Food preservations

Food preservation:

It is the science which deals with the process of slowing down or preventing the process of decay or deterioration of food. Preservation usually involves preventing the growth of microorganism (yeast, bacteria, mold, etc). Maintaining or creating nutritional value, texture, flavour, etc. are all important aspect of food preservations.

Principle of food preservations:

While preserving the food by various method, following principle are involved:

1. Prevention or delay of microbial decomposition or spoilage of food.
2. Prevention of delay of self decomposition of food.
3. Prevention of damage to the food / Mechanical damage.

• Prevention or delay of microbial decomposition or spoilage of food.

1. Killing of microorganisms present in food. (Example : Heat and radiation treatment)
2. Hindering or slowing down the growth and activities of microorganisms. (Example: Low temperature storage, drying , anaerobic condition, etc.)
3. Removing microorganisms from contaminated food such as washings, filteration, centrifugation,etc.
4. Prevent contamination of food from spoilage causing microorganisms i.e. asepsis (keeping out microbes).

• Prevention of delay of self decomposition of food.

1. Destruction of inactivation of food enzyme. (Example: blanching (heating briefly) at about 100*C in water.)
2. Prevention of delay of purely chemical reaction. (Example: Prevention of oxidation by means of antioxidant.)

• Prevention of damage to the food/ Mechanical damage:

1. Proper handling of food during storage and transportation.
2. Protection of food from damage caused by birds, insects, etc.
3. All enzymes are made up of protein expect ribosome (made from RNA)
4. Animal test contains less antioxidant than plant so it is damaged fast.
5. Due to increase in unsaturation also animal fat is damaged fast as its unsaturation is more.

• Methods of food preservations: There are many methods used for food preservations. Some methods are naturally occuring phenomenon, some comprises physical process and some incoude chemical preservatives. Some of the methods of food preservation are as follow :

1. By preventing contamination of food from spoilage causing microorganisms (Asepsis) For example: peels of fruits and vegetables, testa of seeds, shell of eggs/nuts, hide of animals (hide-thick skin) acts as natural barrier (protective covering), which prevents entryof microorganisms into food interior.
2. Removal of microorganisms: It is easier to remove micrrorganisms from liquid in solid food. Some techniques like filteration, centrifiguation, washing friuts and vegetables, trimming, etc. can be done.
3. Maintainence of anaerobic condition. In this method food are preserved by maintaining anaerobic condition by complete filled evacuation of the unfipled space or removal of air by carbondioxide or by inert gases such nitrogen gases.
4. Use of high temperature: In this method, heating below 100*C , heating at about 100*C and heating above 100*C tecnhiques are applied. Pasteurization, boiling, steaming, canning, etc techniques are applied for preservation of food by high temperature.
5. Use of low temperature: This method is mainly applied to retard: 》 Microbial growth and activities. 》Chemical reaction and action of food enzymes, biochemical reaction. 》Insect and pest activities. Methods like cold storage, cellar storage, chilling storage, frozen storage, quick freezing, air blast freezing, etc. are used.
6. Preservation by radiation: Various ionizing radiation like X-ray, Gamma ray,cathode ray, etc and non-ionizing radiation like UV ray are used for food preservation.
7. Preservation by drying or dehydration: In this methods various techniques like evaporation, sublimation, solar drying, use of mechanical dryers, freeze drying, by use of salts and sugar, through smoking, etc. It helps to preserve food for long time period and also prevent them for microorganisms.
8. Use of chemical preservatives (either developed by microorganisms or added in pure form): Various chemical substances can be used as chemical preservatives. The organics acids ans salts (propionic acid and their salts, benzoic acid or benzoites, sorvic acids and sorbates, acetic acid and acetate, boric acids), sulphurdioxide (SO2) , nitrate and nitrite, sugar and salts, smoking and wood smoke, etc.

Advantages of food preservatives:

• It helps the food materials to be preserved for long period of time by slowing down the process of decay and deterioration of food.
• It also slows down the grwthand activities of microorganisms.
• It hepls to preserve nutritional value of food and also preserve its texture and flavour.
• Foods like dairy products (cheese), meat products (sausages,beef, poultry, dried fish product, fruits and vegetables, confectionary baked products, etc. can be preserved by using chemical preservatives like sorvic acids and sorbates.

Disadvantages of food preservatives:

There are no such harmful effects if the preservatives are used in proper amount applying proper techniques. But it may lead to harmful effects if used in excess amount. Some of them are:

• It may bring change in texture and flavour, physical state of food items.
• Nutritional value may deteriorate and food may be non-edible.
• Excess freezing of food items is also not appreciable.

Methods of Food preservations:

• By preventing contamination of food from spoilage causing microorganisms (Asepsis):

Asepsis is a preservation factor of keeping out microorganisms in inner tissues of healthy plants and animals are often free of microorganisms, if present microorganisms donot initate spoilage. Most of the spoilage causing microorganisms enter into food from external sources by contamination. Therefore microbial spoilage of food can be preveneted by prevention of contamination. Some foods have natural barrier (protective covering), which prevent entry of microorganisms into food interior (inner surface). For example : Peels of fruits and vegetables, testa of seeds, shell of eggs/nuts, hide of animlals (hide-thick-skin) In food industries, high attention is given to prevent contamination of food from raw materials to finish product. Pcakaging of food is widely used application of asepsis in industries. Packaging can be done using loose cartoons, wrappers, sealed container or cans. Similarly, sanitary method and personal hygiene are too important factor to minimize contamination of food.

• Removal of microorganisms from food:

If contamination of food by spoilage causing microorganisms isnot prevented, food can be still protected from microbial decomposition by removing contamination from food. Microbial decomposition, it is easier to remove microorganisms from liqiud food than from solid food. Some techniques of removing microorganisms include:

1. Filtration: Filtration is most widely and sucessfully used method for complete removal of microorganisms. This method is only applicable for clear liqiuid like fruit juice, beer, soft drinks, water, etc. The liquid is filtered through previously sterilized microbial proof filter.
2. Centrifugation: This is that method which removes microorganisms to very small extents, from liquid food. Centrifugation at high speed sediments are suspended particles and cells.
3. Washing fruits and vegetables : Washing remove number of microorganisms, if the water used for washing is of good quality. However, washing increases water activity of some food and thus make it suitable for growth. This method is commonly used to remove microorganisms and dust from fruits and vegetables.
4. Trimming: Trimming is the process of removing spoiled part of food by cutting. If spoiled portion of food is removed, transmission of microorganisms to healthy part of food can be prevented. This method is also commonly used for fruits and vegetables.

• Maintainence of anaerobic condition:

Maintainence of anaerobic condition in a container by a complete filled evacuation of the unfilled space (head space) or replacement of air by C0₂or by gases such as nitrogen will bring about anaerobic condition. Spores of some of the anaerobic spore formers are especially resistance to head and may survive incanned food but be unable to germinate or grow in absence of oxygen, fermentative product of CO₂and accumulation at the surface create anaerobic condition, and prevent the growth of aerobes.

Refrence:

1. Jay, MJ. Modern Food Microbiology. 3rd. Delhi: CBS Publications and Distributors, 1987
2. Frazier, Wc and Westhoff DC. Food Microbiology. 3rd. New-Delhi: Tata MCGraw-Hill Publishing Company Limited, 1986.