When food is available more than the present use, it is preserved for future consumption. “Food preservation is a technique to increase the self life of the products of perishable items.”
Foods such as fruits and vegetables have a short growing season and preservation makes them available to use throughout the year and avoid wastage of surplus crops.
Preserved food is easier to distribute and can be made available in all places at all time.
PRINCIPLES OF FOOD PRESERVATION:
Prevention or delay of microbial decomposition:
A). By keeping out micro-organisms (asepsis)
B). By removal of micro-organism e. g. by filtration
C). By killing the micro-organisms e. g. by heat or radiation
D). By hindering the growth and activity of micro-organism e. g. by low temperature, drying, anaerobic conditions or chemicals
Prevention or delay of self decomposition of food:
- By destruction or inactivation of food enzymes, e.g. by blanching
- By delay of chemical reactions, e.g. by prevention of oxidation by means of an antioxidant.
Prevention of damage caused by insects, animals and mechanical causes
FOOD PRESERVATION METHODS:
- PRESERVATION BY LOW TEMPERATURE
- PRESERVATION BY HIGH TEMPERATURE
- PRESERVATION BY PRESERVATIVES
- PRESERVATION BY OSMOSIS
- HURDLE TECHNOLOGY
- FOOD IRRADIATION
FOOD PRESERVATION BY LOW METHOD:
Cold temperature chiefly inhibit growth of micro-organisms although freezing may result in the destruction of some micro-organisms.
- SLOW FREEZING
- QUICK FREEZING
- DEHYDRO FREEZING
- MEAT AND POULTRY
EFFECT OF FREEZING ON NUTRITIONAL VALUE:
- Freezing itself has little effect on the nutritive value of foods
- There is some loss of water-soluble vitamins in preparation of vegetables for freezing.
- Loss of ascorbic acid occur during storage if the temperature is much above -18 degree C.
PRESERVATION BY HIGH TEMPERATURE:
- The temperature and time used in heat processing a food depend upon the effect of heat on food and the other preservative methods employed.
NUTRITIVE VALUE OF CANNED FOOD:
It compares favourable with that of fresh foods losses in canning are minimized by:
- Using newer methods which involves a short high temperature heating process followed by rapid cooling.
- Exhausting air from than can before it is sealed has cut down the oxidative losses of vitamins.
PRESERVATION BY PRESERVATIVES:
- Preservatives has been defined by Jacob as “chemical agents” which serve to retard hinder or mask undesirable change in food.
- The changes may be caused by micro-organisms, by enzymes of food or by purely chemical reactions.
DEFECTS IN CHEMICAL PRESERVATIONS:
- SO2 has got suffocating property and many consumers do not like it although it is advantageous in retention of vitamin C and retardation of non enzymatic browning in fruit and vegetable products.
- Benzoic acid is not advisable to be used in lime juice products as it induces browning in such products.
- Food preservatives are often used in mixed form or in conjunction with other methods of preservation. E.g.
PRESERVATION BY OSMOSIS:
- By the principle of osmosis, jam, jellies and pickles are preserved.
- Plasmolysis of microbial cells occur.
- Water is withdrawn from microbial cells when they are placed in solutions containing large amounts of dissolved substances such as sugar or salt.
- As a result of this water loss, microbial metabolism is halted.
- The antimicrobial effect of this water loss are similar in principle to metabolic in habitation by dehydration.
TYPES OF OSMOSIS PRESERVATION:
A). HIGH CONCENTRATION OF SUGAR:
- JAM & JELLIES:
- COMMERCIAL PECTIN
- GEL FORMATION
- ALCOHOL TEST
POINTS TO BE REMEMBER DURING EXTRACTION OF PECTIN:
- The maximum quantity of pectin is extracted in an acid solution.
- If fruits are rich in pectin but low in acidity, acidifying the solution before cooking, increases the viscosity of the extraction.
- High viscosity of the solution is closely related to good jellying power.
- Cooked extractions contains more pectin than raw juices.
- Short periods of cooking yield extractions of better jellying power than does long boiling.
B). HIGH CONCENTRATION OF SALT
- Foods are also preserved by the principle of osmotic pressure in salting and pickling.
- Most commonly used inorganic preservative is sodium chloride.
- It is used in brine solutions or is applied directly to the food.
- Enough may be added to slow down or prevent the growth of micro-organisms or only enough to permit lactic acid, fermentation to take place.
- Sodium chloride
- Spices and other condiments
PRESERVATION BY DEHYDRATION:
- This is a very popular and ancient method of preservation where the foods are preserved by drying.
- Drying as a means of preservation can be observed in cereal grains, legumes and nuts which dry on the plants.
PRINCIPLES OF REMOVING MOISTURE:
- Surrounding the food with warm air which has the capacity for holding more moisture than does cool air.
- Circulating air, which constantly brings a fresh supply of air into contact with food.
- Dye-dipping as the case of prunes to make skins more permeable to water.
- Dicing the food into small pieces which exposes more surface to the action of heat or air.
TREATMENT OF FOOD BEFORE DRYING:
- Selecting and sorting for size, maturing and soundness.
- Washing especially of fruits and vegetables.
- Peeling of fruits and vegetables by hand, machine, lye bath or abrasion.
- Subdivision into halves, slices, shreds or cubes.
- Blanching or scalding of vegetables and some fruits like apricots and peaches.
VARIOUS METHODS OF DRYING:
- Freeze drying
- Sun drying
- Drying osmosis
- Drying by mechanical driers
- Spray drying
- Foam mat drying
- Drying by smoking
FOOD IRRADIATION METHOD:
- It is a process of food preservation in which food is exposed to ionizing energy-radioisotope cobalt – 60 and caesium -137.
- High energy electrons and X-rays generated by machines using electricity are increasingly used for food irradiation.
POTENTIAL USES OF IRRADIATION:
- To extend shelf life of meat, poultry and sea foods by killing microorganisms causing their spoilage.
- To enhance safety of food by killing food borne pathogenic micro-organisms and parasites by changing the structure of DNA and
RNA of micro-organisms.
- To replace chemicals for inhibiting sprouting in tubers and bulbs and delaying ripening of fruits.
HURDLE TECHNOLOGY MEHTODS:
- Hurdle technology foods are defined as products whose shelf life and the microbiological safety are extended by use of several factors none of which individually would be totally lethal towards spoilage or pathogenic microbes.
- Combined process
- Combined methods
- Combination preservation
- Combination technique or
- Barrier technology
SIGNIFICANCE OF HURDLE TECHNOLOGY:
- An intelligent application of hurdle contributes to both improvement in product quality and sustainability,
- Calculated application of hurdles could result into saving money, energy and several resources.
- Each hurdle contribute to the safety net against the microorganism.
- Since SSPs do not require refrigeration, they travel long distance for finding place in the market to reach the consumers.
- Able to use in products for defense force
- Perishability can be reduced.
POTENTIAL HURDLE FOR USE IN PRESERVATION:
- PHYSICAL HURDLES
- PHYSICO-CHEMICAL HURDLES
- MICRONBIALLY DERIVED HURDLES
- MISCELLANEOUS HURDLES