T fst - 13 Principles.ppt
- 1. 1 PRINCIPLES OF FOOD PRESERVATION Activities of spoilage agents depend on several factors Change in any of these results in their decreased performance Principles of food preservation based on: Knowledge about spoilage agents Understanding of how: chemical reactions physical changes pest attack collectively reduce quality of foods
- 2. 2 PRINCIPLES OF FOOD PRESERVATION Principle 1 Autolysis in food may be prevented or delayed by: destruction or inactivation of enzymes by treatment and handling of food in such a manner so as to inhibit reactivity of chemically active molecules
- 3. 3 Principle 2 Spoilage in foods as a result of microbial activity may be prevented or delayed by: either prohibiting entry of microorganisms into the food physically removing them from the food hindering their growth and activity or even destroying them, if they are already present in the food.
- 4. 4 Principle 3 Quality defects and losses in food caused by insects, rodents and birds may be controlled by: adequate packaging and by instituting a sustained population control programme of such pests
- 5. 5 Principle 4 Deterioration in food caused by the physical phenomenon occurring during processing, handling and storage may be reduced by: development of optimal handling, processing and storage conditions
- 6. 6 PREVENTION OR DELAY OF AUTOLYSIS Enzymes require specific pH range to catalyze life reactions Enzymes sensitive to changes in pH of environment Information utilized to preserve foods by merely altering their pH
- 7. 7 PREVENTION OR DELAY OF AUTOLYSIS For example Biological preservation of vegetables (pickling): pH of raw materials reduced through activities of lactic acid bacteria Some meat and milk products preserved or produced as a result of change in pH Sometimes organic acids, as acetic acid (vinegar), added to foods for the purpose
- 8. 8 PREVENTION OR DELAY OF AUTOLYSIS Enzymes thrive best in particular temperature range Deviation - higher or lower side has adverse effect on enzyme activity Food subjected to high temperature will either destroy or inactivate enzymes Process called blanching or scalding
- 9. 9 PREVENTION OR DELAY OF AUTOLYSIS Blanching or scalding Some fruits, most vegetables normally subjected to around 100°C for few seconds to few minutes Destroys some damaging enzymes – catalase Usually pre-treatment in food preservation methods as: Canning Dehydration Freezing
- 10. 10 PREVENTION OR DELAY OF AUTOLYSIS Use of low temperature - procedure employed to delay autolysis Low temperatures that prevail in refrigerator or cold storages retard enzyme reactions Refrigeration delays ripening process in fruits Freezing inactivates enzymes and sometimes destroys them Hence frozen foods have much longer shelf life than fresh or those kept at above 0°C
- 11. 11 PREVENTION OR DELAY OF AUTOLYSIS Enzymes require moisture for biochemical reactions catalysed in foodstuffs Absence of water means no reaction Property utilized, partly, in preservation of foods by: Removal of moisture Binding of moisture
- 12. 12 PREVENTION OR DELAY OF AUTOLYSIS Moisture in foods removed by: Sun drying Dehydration Concentration Evaporation Available moisture bound by using chemicals: production of intermediate moisture foods (jam)
- 13. 13 Prevention or Delay of Autolysis Chemically induced autolysis: minimized by applying good manufacturing practices (GMP) based on experience and scientific knowledge Most chemical reactions retarded by: Maintaining low temperature Use of chemical inhibitors Packaging
- 14. 14 Prevention or Delay of Autolysis Non-enzymatic changes prevented by: Use of some chemicals Sulphites to inhibit colour changes Antioxidants check rancidity
- 15. 15 Prevention or Delay of Autolysis Further control achieved by: Employing low temperature Controlling water activity in dehydrated foods Reduction of reducing sugars in potatoes by storage Reduction of amino-nitrogen content in juices by ion exchange Packaging with oxygen scavengers
- 16. 16 Prevention or Delay of Microbial Activity Microorganisms invaders Where undesirable treat like any other invader 1. Take precautions to prevent their entry into food 2. Where already gained access, may be thrown out 3. When such strategy not feasible, control microbial activities by creating unfavourable conditions 4. Destroy by any suitable means
- 17. 17 Keeping Microorganisms Out Nature creates all foods free from microorganisms Provides protective covering to prevent entry All fruits, vegetables free from microorganisms when produced Skin, peel, husk and shell provide protection Tissues of healthy animals free from microorganisms Skin and fatty tissues give animal protection
- 18. 18 Keeping Microorganisms Out When outer covering injured, microorganisms invade and start growing, cause infection Industry provides protective covering to guard against entry of microorganisms from outside source: Pack fruits, vegetables, meat, etc in tin cans or glass containers Coat cheese, eggs etc with wax or other inert material
- 19. 19 Removal of Microorganisms During food processing difficult to keep microorganisms out Gain entry into food during harvesting storage processing operations Microorganisms very small, not easy to pick and throw out
- 20. 20 Removal of Microorganisms Fruits and vegetables carry microflora on their surface or in bruised, damaged and decaying tissues Wash raw material thoroughly to remove contaminants Trim bruised, damaged and decayed portions Filter or centrifuge liquid foods such as clear beverages (water, fruit juices) Centrifuge milk to separate cream – removes microorganisms
- 21. 21 Creation of Unfavourable Conditions Most food spoilage and pathogenic microorganisms aerobic Spores of some organisms need oxygen to germinate Creating anaerobic conditions: Prevents growth of vegetative cells Prevents germination of spores In canning use mechanical vacuuming or exhausting Air from product removed, can sealed airtight Even if microorganisms gained entry, under prevailing anaerobic conditions, will not grow Anaerobic organisms may pose problem if their activities not checked or not subsequently destroyed.
- 22. 22 Creation of Unfavourable Conditions Removal or binding of moisture All microorganisms require available moisture for activity Growth inhibited if no or low moisture Preserve food by removal or binding of moisture remove by drying, dehydration, concentration
- 23. 23 Creation of Unfavourable Conditions Moisture made unavailable by chemicals: Sugar Glycerine Humectants (water-binding substances) Microorganisms unable to grow in changed environment Food does not deteriorate or spoil as a result of microbial activity.
- 24. 24 Creation of Unfavourable Conditions Chemicals produce unfavourable conditions: Some chemicals intentionally added Sulphur dioxide - as potassium metabisulphite Benzoic acid as sodium benzoate protect fruit juices from spoilage in sealed containers Some chemicals developed Lactic acid
- 25. 25 Creation of Unfavourable Conditions Lactic acid produced by normal growth of lactic acid bacteria Activities of lactic acid bacteria encouraged in: Vegetable pickles - Grow, produce lactic acid, reduce pH of vegetable material In dairy and meat industries some products produced and preserved by lactic acid bacteria Examples - Sour cream, butter, cheeses, yoghurt and sausages
- 26. 26 Creation of Unfavourable Conditions Low temperature another effective tool to create unfavourable conditions Chilling slows microbial growth Freezing completely stops activities Holding foods at freezing temperature or in frozen state helps destroy or kill some microorganisms.
- 27. 27 Destruction of Microorganisms Destroy microorganisms to prevent spoilage High temperatures (above maximum growth temperature) adversely affect microorganisms Blanching destroys or inactivate enzymes Also kills some vegetative microorganisms Pasteurization temperatures (65°C to 88°C) kill pathogenic organisms including bacteria and yeasts in some liquid foods Sterilization employs much higher temperatures (100°C or above) to destroy all microbial forms
- 28. 28 Destruction of Microorganisms Sterilization not possible in food processing Hence commercial sterilization or heat processing employed Some microorganisms or spores remain viable after this With combination of other techniques employed in preservation method, these remain dormant and unable to cause trouble
- 29. 29 Destruction of Microorganisms Heat treatment necessary to kill microorganisms or their spores varies: Organism to organism State - vegetative or spore Environment Depending on effectiveness of heat treatment, only part of vegetative cells, or all or most of the cell may be destroyed Some bacterial spores also killed at high temperature Heat treatment applied temperature/time dependent.
- 30. 30 Destruction of Microorganisms Some chemicals very effective in controlling microbial activity in foods Sulphur dioxide and benzoic acid common in fruit and vegetable preservation industry Propionates employed in baking for moulds Microorganisms also destroyed by radiations Ultraviolet waves from electromagnetic spectrum have germicidal properties Gamma rays, emitted from by-products of atomic fission germicidal, preserve food.
- 31. 31 Control of Pest Activities Pests - Insects, rodents and birds Only those so designated that: exhibit prolific reproductive capabilities compete with humans for food and space may transfer diseases to man Constant threat to man's survival Seemingly harmless species a necessary part of balanced ecological system in which we live.
- 32. 32 Insects Insects destroy and waste almost 50% annual cereal grain crops in some developing countries Attack food everywhere - field, processing plants Eat sizeable quantities Damage and create easy entry for microorganisms Control - fumigation with methyl bromide, ethylene oxide and phostoxin
- 33. 33 Insects Protect from further infestation - packing in containers Insect-proof packaging not feasible for all dried foods, especially in developing countries for both economic and logistic reasons Use integrated systematic insect control program: preventive measures curative measures
- 34. 34 Insects Typical preventive measure for insect control: Treatment with long-acting insecticides Treatment with insect repellants for seeds Use of insect predators Other biological means Curative insect control program - extermination of insects and insect eggs from food by: Physical methods Chemical methods Biological methods
- 35. 35 Insects Popular physical method for destroying insect eggs in wheat flour and other similar size- reduced dry foods involves use of impact-based instrument, the entolater Insect eggs thrown to metal body of this revolving instrument instantly destroyed by impact
- 36. 36 Insects Heat disinfection another physical method to destroy insects in stored products Temperature of food raised to about 50°C since insects cannot survive such high temperature Infrared devices popular heat sources for heat disinfection of grains - effective and relative low cost
- 37. 37 Insects Most desirable control measures: Demonstrate effective insect control over long periods without creating intractable adverse effects on man and the environment Control measures which momentarily and indiscriminately reduce insect populations may introduce serious health hazards and environmental problems in the long run.
- 38. 38 Rodents Gross rodent infestation readily discovered by: presence of burrows dark oil and dirty stains on rodent runaways odour of mice filth deposited on food damaged food and other materials Dry urine appears as darkened stain on food and containers These stains will fluoresce under ultraviolet light Presence of rodent filth in food processing and storage premises calls for prompt control measure.
- 39. 39 Rodents Complete eradication almost impossible Situation worse in developing countries rodent populations overwhelm available control facilities due to poor environmental sanitation Systematic control of mice and rats practiced with reasonable degree of success in most industrialized countries Typical systematic control includes use of poison baits rat-traps biological methods
- 40. 40 Rodents Rodent harbourages usually destroyed or sealed off after treatment with long-acting rodenticide Foods packaged and stored in environments that make rodent invasion difficult Sustained control effort can yield positive results Must be backed by reasonable measure of sanitation around food handling and storage sites.
- 41. 41 Birds Birds consume substantial quantities of grains in field Some birds, as weaverbird, known to devastate entire corn crop in field Loss by bird invasion traditionally checked by installing noise-making dummies at strategic points on farm to scare birds away Birds consume grains, contaminate food and water Prevention Erect bird screens over important water supply sources and food handling areas.
- 42. 42 Reduction In Physical Defects Interactions induced by series of treatments that accompany food manufacture, handling and storage No simple rule of thumb to predicts best processing conditions for all types of foods Experimentation, experience and current exchange of scientific and technical information on effects of various processing variables on food quality have helped in development of optimized processes aimed at keeping physical defects in foods to minimum.
- 43. 43 Surface Drying Desiccation or drying out observed on surface of certain foods during frozen storage an important physical defect Control - adequate packaging and maintenance of steady storage temperature Refrigerated storage of flesh foods - moisture loss and surface drying minimized by maintaining higher than conventional average relative humidity in storage chamber Increase in microbial activity induced by such high relative humidity kept under check by use of ultraviolet lamp as storage atmosphere sterilants
- 44. 44 Crystallization Common physical defect - crystallization of sugar in syrups and sugar-based products Products develop distasteful sandy texture Unwanted sugar crystallization prevented by using mixture instead of single sugar 60 % sucrose solution at ambient temperature develops crystals Solution containing 75 % total sugars, blend of sucrose, glucose and fructose no crystals Knowledge applied in production of high sugar products – jams, sugar-based jellies
- 45. 45 Other Defects Attempts at reducing physical and textural defects in foods during processing and storage are seen in process handling and storage controls applied by the industry Relative humidity and drying rates controlled in dehydrators to minimize incidence of case- hardening; Stabilizers used to prevent collapse of emulsions during handing and storage Freeze-drying removes moisture from heat-sensitive foods and enhances retention of natural nutritional and textural properties on rehydration.
- 46. 46 Thanks