Food preservation is known “as the science which deals with the process of prevention of decay or spoilage of food thus allowing it to be stored in a fit condition for future use”. Preservation ensures that the quality, edibility and the nutritive value of the food remains intact. Preservation involves preventing the growth of bacteria, fungi and other microorganisms as well as retarding oxidation of fats to reduce rancidity. The process also ensures that there is no discolouration or aging. Preservation also involves sealing to prevent re-entry of microbes. Basically food preservation ensures that food remains in a state where it is
- not contaminated by pathogenic organisms or chemicals
- does not lose optimum qualities of colour, texture, flavor and nutritive value
Drying is the oldest method of food preservation. This method reduces water activity which prevents bacterial growth. Drying reduces weight so foods can be carried easily. Sun and wind are both used for drying as well as modern applications like Bed dryers, Fluidized bed dryers, Freeze Drying, Shelf dryers, Spray drying and Commercial food dehydrators and Household oven. Meat and fruits like apples, apricots and grapes are some examples of drying with this method.
Freezing is keeping prepared food stuffs in cold storages. Potatoes can be stored in dark rooms but potato preparations need to be frozen.
Smoking is the process that cooks, flavours and preserves food exposing it to the smoke from burning wood. Smoke is antimicrobial and antioxidant and most often meats and fish are smoked. Various methods of smoking are used like Hot smoking, Cold smoking, Smoke roasting and Smoke baking. Smoking as a preservative enhances the risk of cancer.
Vacuum packing creates a vacuum by making bags and bottles airtight. Since there is no oxygen in the created vacuum bacteria die. Usually used for dry fruit.
Salting and Pickling: Salting also known as curing removes moisture from foods like meat. Pickling means preserving food in brine (salt solution) or marinating in vinegar (acetic acid) and in Asia, oil is used to preserve foods. Salt kills and inhibits growth of microorganisms at 20% of concentration. There are various methods of pickling like chemical pickling and fermentation pickling. In commercial pickles sodium benzoate or EDTA is added to increase shelf life.
Sugar is used in syrup form to preserve fruits or in crystallized form if the material to be preserved is cooked in the sugar till crystallization takes place like candied peel and ginger. Another use is for glazed fruit that gets superficial coating of sugar syrup. Sugar is also used with alcohol to preserve luxury foods like fruit in brandy.
Lye also known as Sodium hydroxide turns food alkaline and prevents bacterial growth.
Canning and bottling means sealing cooked food in sterile bottles and cans. The container is boiled and this kills or weakens bacteria. Foods are cooked for various lengths or time. Once the can or bottle is opened the food is again at risk of spoilage.
Jellying is preserving food by cooking in a material that solidifies to form a gel. Fruits are generally preserved as jelly, marmalade or fruit preserves and the jellying agent is pectin that is naturally found in fruit. Sugar is also added.
Potting is a traditional British way of preserving meat by placing it in a pot and sealing it with a layer of fat.
Jugging is preserving meat by stewing it in an earthenware jug or casserole. Brine or wine is used to stew meat in and sometimes the animal’s blood.
Burial in the ground preserves food as there is lack of light and oxygen and it has cool temperatures, pH level, or desiccants in the soil. Used to preserve cabbages and root vegetables.
Pulsed Electric Field Processing is a new method of preservation that uses brief pulses as strong electric field to process cells. This is still at an experimental stage.
Modified atmosphere preserves food by operating on the atmosphere around it. Salad crops that are difficult to preserve are packaged in sealed bags with an atmosphere modified to reduce the oxygen concentration and increase the carbon dioxide concentration.
Controlled use of organism is used on cheese, wine and beer as they are preserved for a longer time. This method uses benign organisms to preserve food by introducing them to food where they make an environment which is not suitable for harmful pathogens to grow.
High pressure food preservation is a method that presses foods inside a vessel by exerting 70,000 pounds per square inch or more of pressure. This disables microorganisms and prevents spoilage but food retains its appearance, texture and flavour.
Modified Atmosphere Packaging extends the shelf life of fresh food products. The atmospheric air inside a package is substituted with a protective gas mix which ensures that the product will stay fresh for as long as possible.
Various food preservation techniques to increase shelf-life of the products*
|Method||Effect on microbial growth or survival|
|Refrigeration||Low temperature to retard growth|
|Freezing||Freezing Low temperature and reduction of water activity to prevent microbial growth, slowing of oxidation reactions|
|Drying, curing and conserving||Reduction in water activity sufficient to delay or prevent microbial growth|
|Vacuum and oxygen free modified atmosphere packaging||Low oxygen tension inhibits strict aerobes and delays growth of facultative anaerobes|
|Carbon dioxide enriched and or modified atmosphere packaging||Specific inhibition of some micro-organisms|
|Addition of weak acids; e.g. sodium lactate||Reduction of the intracellular pH of micro-organisms|
|Lactic fermentation||Reduction of pH value in situ by microbial action and sometimes additional inhibition by the lactic and acetic acids formed and by other microbial products. (e.g. ethanol, bacteriocins)|
|Sugar preservation||Cooking in high sucrose concentration creating too high osmotic pressure for most microbial survival.|
|Ethanol preservation||Steeping or cooking in Ethanol produces toxic inhibition of microbes. Can be combined with sugar preservation|
|Emulsification||Compartmentalisation and nutrient limitation within the aqueous droplets in water-in-oil emulsion foods|
|Addition of preservatives such as nitrite or sulphite ions||Inhibition of specific groups of micro-organisms|
|Pasteurization and appertization||Delivery of heat sufficient to inactivate target micro-organisms to the desired extent|
|Food irradiation (Radurization, radicidation and radappertization)||Delivery of ionising radiation to disrupt cellular RNA|
|Application of high hydrostatic pressure (Pascalization)||Pressure-inactivation of vegetative bacteria, yeasts and moulds|
|Pulsed electric field processing (PEF treatment)||Short bursts of electricity for microbial inactivation|
* The contents of the table have been sourced from the information document from FSSAI & CODEX.