BY: RAHUL ANDHARIA (MSIWM001)
- The process of handling and treating food to prevent it from getting spoiled is termed as food preservation.
- Food has to be generally protected from bacteria, fungi and other microorganisms as well as retarding fat oxidation which can lead to rancidity.
- The term preservation simply means use of chemical compound or process to stop the growth of microorganisms and to prevent food spoilage.
- Preservation of food in hermetically sealed containers was the very first method implied in food preservation. This method was introduced by Nicholas Appert in 1700s.
- Oldest method used for food preservation known to be used was Food Drying (originated in middle-east as per ancient records).
Principles of food Preservation:
- Prevention of microbial decomposition: Asepsis (keeping out microorganisms), removing microorganisms, hindering microbe’s growth by low temperatures, drying, chemicals and by using anaerobic conditions.
- Prevention of self-decomposition of food: by inactivating or destructing food (blanching), preventing delay of chemical reactions (using anti-oxidants).
Methods of food preservation:
- It simply means keeping out microorganisms from food.
- Microbial decomposition is delayed or protected if there is protective covering above the food like shells of nuts, skin of fruits and vegetables, membranes or fat on meat and fish.
- When the protective covering is damaged, it can lead to decomposition of inner tissues by microorganisms.
- Packaging of food is the widely used application of asepsis. The packaging may range from a loose wrapping to hermetically sealed container of canned foods.
- In the dairy industry, contamination with microorganisms is avoided as much as in practicable in the production and handling of market milk.
- In the meat packaging industry, sanitary methods of slaughter, handling and processing of meat reduces the load of microorganisms.
- In canning industries, load of microorganisms determines the heat process necessary for preservation of food.
- Removal of microorganisms: Removal of microbe’s can be accomplished by methods like filtration, centrifugation, washing and trimming.
- The liquid is filtered through previously sterilized bacteria-proof filter made up of sintered glass, diatomaceous earth, unglazed porcelain, and membrane pads.
- The liquid is than forced through by applying positive and negative pressure.
- Used for fruit juices, beer, soft drinks and water.
- This is the only successful method for complete removal of microorganisms.
- This method is used in treatment of drinking water.
- When it is applied to milk, the main purpose is to take out suspended particles other than bacteria.
- Centrifugation at high speeds removes most of the space.
- Washing raw foods can be helpful in their preservation but may be harmful under certain conditions.
- Washing fruits and vegetables removes soil microorganisms that may be resistant to heat process during canning process of these foods.
- Trimming of spoiled portions of food or discarding spoiled samples is important to avoid eating spoiled food which may lead to food poisoning.
- Maintenance of anaerobic conditions:
- A preservative factor is sealed. Packaged foods may be in the anaerobic conditions in the container.
- A complete fill, evacuation of unfilled space or replacement of the air by co2 or by inert gas such as N2 will bring about anaerobic conditions.
- Spores of some aerobic organisms are especially resistant to heat and may survive in canned foods, but will not be able to germinate under anaerobic conditions.
- Production of C02 and during fermentation and its accumulation at the surface will serve to make conditions anaerobic there and prevent the growth of aerobes.
- Use of high temperatures:
- Process of slow heating is known as Pasteurization. It can kill some microorganisms but not all.
- Usually involves the application of temperature below 100 degree Celsius.
- The heating can be done by means of steam, hot water, dry heat and electric currents.
- Time and temperature used in this process depends upon the method employed and the product treated.
- The high temperature-short time method employs comparatively higher temperatures for a short period of time.
- The low temperature-long time method uses a lower temperature for a longer time.
- Example: Grape wine pasteurization for 1min at 82-85 degree Celsius in bulk.
- Canning can be defined as preservation of food in sealed containers and usually implies heat treatment as the principle factor.
- Canning is done using Tin cans or in glass containers.
- Raw food for canning is freshly harvested, properly prepared, graded and washed thoroughly before used for canning.
- Many vegetable foods are blanched briefly by hot water or steam before packaging.
- Blanching washes the food further, sets color, and kills microorganisms.
- Use of low temperature:
- At lower temperatures, chemical reactions, enzyme action and microbial growth will be much slower.
- In this temperature is not far above freezing.(-1 degree Celsius)
- Generally refrigerators are used at 0-8 degree Celsius for preserving food products.
- Most perishable foods like eggs, dairy products, meat, and seafood can be held in chilling storage refrigerators for a limited time with a very little change from their original condition.
- Process of Enzymatic and microbial changes in food cannot be prevented by this method, but the process is slowed down to great extent.
Freezing or Frozen storage:
- The rate of freezing of foods depends on the method employed, temperature used, circulation of air and the type of food to be freeze.
- The temperature is usually -23.3 degree Celsius or (lower to -15 to -29 degree Celsius) and takes 3-72 hours for the process.
- It is limited to climates with high temperatures and dry atmosphere and to certain types of fruits like apricots, peaches and pears.
- This process takes longer time than other processes.
- Involves passage of hot air with controlled relative humidity over the food to be dried.
- The simplest dryer is the evaporator or Kiln, where the natural draft from the rising of hot air brings about drying of food.
Freeze drying: freeze drying or sublimation of water from a frozen food by means of vacuum and applied heat at drying shelf can be used in number foods like meat, poultry, seafood, vegetables and fruits.
- Preservation by food additives:
- Food additives are specifically added to prevent decomposition or deterioration of food. The food additives used for this purpose are called as chemical preservatives.
- They inhibit microorganisms by inhibiting their cell membrane, enzyme activity or their genetic mechanism.
- Factors that influence effectiveness of chemical preservatives in inhibiting microorganisms are: concentration of chemical, temperature, time, chemical and physical characteristics of substrates in which organism is found.
- Food additives added include organic acids, salts, sugars and spices.
- Salting helps in preserving fruits for a longer duration.
- Sodium benzoate, vinegar, and sodium metabisulphite which are known as synthetic preservatives can also be added.
- Preservation by Radiation:
- This method can also be called as cold sterilization.
- Surface contamination of several foods can be prevented or reduced by this method. Radiations like UV rays, X-rays and gamma rays are used to kill microorganisms.
- Example: low level of radiations can be used on fruits and vegetables to kill insects and prevent food from spoilage.
Food preservation is essential in terms of protecting food from microbes and environmental conditions and to store food for longer duration of time.
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