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FOOD PRESERVATION TECHNIQUES SMG
- 1. FOOD PRESERVATION TECHNIQUES DrSaji Mariam George Associate Professor Assumption College Autonomous Changanacherry
- 2. FOOD PRESERVATION TECHNIQUES Foodpreservation – the process of prevention of decay and spoilage of food. • Increase the shelf life of food • Make the seasonal food available through out the year • Add variety to the diet • Save time by reducing preparation time and energy • Stabilizes prices of food • Increase the availability of food – improve the nutrition of the people.
- 3. Method varies withthe length of storage intended. 1. DEHYDRATION(DRYING OR DESICCATION) • Removal of water from the food • Food containing 10% or less of free moisture are not subjected to spoilage by microbes – unable to grow . • Dehydrated food → keep in air -tight containers- not exposed to fluctuations in humidity.
- 4. a). SUNDRYING • Heatfrom Sun is used for drying • Materials prepared by suitable methods are placed on shallow trays in sunlight. e.g. Raw Mango, Raisins, Dates , Figs, Tapioca chips , Bitter gourd & Chilly “kondattams” , Pappad , Fish, Meat, Prawns, Grains etc.
- 5. b). SMOKING Food driedby exposing them to smoke by burning special wood - mahogany, apple, walnut etc. • Heat from smoke helps in removal of moisture • Exposure to smoke imparts a characteristic flavour. • Certain bactericidal substances may be formed during smoking ( formaldehyde, phenols, cresols) and this also helps in preserving the food to a limited extent. E.g. – Fish, Meat (esp. Beef)
- 6. c). MECHANICAL DRYING •Temperature and humidity are controlled • Products with superior quality, better colour, correct texture and right flavour can be obtained. i) Dehydrators Food materials are spread in thin layers on metal trays and inserted in the dehydrator and dried by heat. E.g. - Pappad, Green peas, Potato, Jack fruit etc.
- 7. ii) Roller dryers •Finely ground wet suspension of food is spread as a thin layer on a revolving drum which is heated. • Dry powder is then scrapped off and packed. iii) Spray dryers • Food in the form of a liquid or a finely ground suspension is pumped through a fine jet and falls as a fine spray into a chamber through which hot air is circulated. • The fine droplets of the liquid quickly lose their moisture by evapouration and fall on the floor of the chamber as a fine powder. e.g. Instant coffee, tea, milk powder, gelatin etc.
- 8. d). Salting • Bindingmoisture by addition of salt – prevents growth of microbes • Salt produces high osmotic pressure and causes destruction of microorganisms by plasmolysis. • Dry salting is used in the preservation of Tamarind Raw mango Fish Meat etc.
- 9. e). Pickling • Avery common food preservation technique • Right amount of salt, chilly, turmeric , asafoetida , oil. Vinegar etc. used in pickling helps to preserve food. • A layer of oil on top - prevents the growth of moulds and yeasts by preventing exposure to air.
- 10. f). Adding sugar •High concentration of sugar binds moisture in the food – water is unavailable for microbes to grow . e.g Jam Jelly Marmalade (using orange) Sweetened condensed milk.
- 11. g) Freeze Drying(Lyophilization) • Food is preserved by rapid freezing and dehydration of the frozen material under high vacuum. • Food is preserved in its natural state - no loss of texture /flavour • Food is packed in plastic or Aluminium foil packets in an atmosphere of Nitrogen Used for the preservation of • Meat • Poultry • Sea foods • Fruits • Vegetables.
- 12. 2. USE OFCHEMICAL PRESERVATIVES & FOOD ADDITIVES Food additive- a substance or mixture of substances added to food • Preservatives • Colours • Flavouring agents • Antioxidants • Emulsifying & stabilizing agents • Antibiotics etc.
- 13. Chemical preservatives • Afood additive - arrest or prevent spoilage by microbes i) Citric acid • To increase acidity and prevent mould growth - fruit squash, jams, jellies • To flavour extracts, candies • To adjust pH to 5 – Fish • To prevent discolouration - Crab meat • As a dip to delay browning – sliced Peaches.
- 14. ii) Benzoic acid& its salts Effective to inhibit the growth of bacteria, yeasts & moulds Sodium benzoate is used in • Jams • Jellies • Carbonated beverages • Fruit juices etc.
- 15. iii) Sorbic acid& its salts (Calcium, Sodium & Potassium salts) • Effective against moulds, yeasts and many bacteria. • Used as a direct antimicrobial additive in foods • As a spray, dip or coating on packaging materials • To prevent refermentation and souring of wine – A combination of 225 ± 25 mg Potassium sorbate and a 30 ± 10 mg free SO2 prevent refermentation and souring of wine.
- 16. Widely used inbakery & confectionary products – Cakes Fillings for chocolate Cheese Beverages Dried fruits Bread Fruit juice Jellies Jams etc.
- 17. iv) Acetates -derivatives of Acetic acid – Vinegar (4% Acetic acid), Sodium diacetate More effective against yeasts and bacteria than moulds. • Vinegar is used in pickles, Mayonnaise etc. • Sodium diacetate is used in cheese spreads • As a treatment for wrappers for butter .
- 18. v) Sulphur dioxide& sulphites(Potassium metabisulphite, Sodium metabisulphite) SO2 – used to treat drying fruits, molasses Sulphites – added to wine as preservative Potassium metabisulphite is used in canning
- 19. vi) Nitrites &Nitrates (Sodium & Potassium salts) • Inhibitory effect on bacterial growth. • Inhibit the formation of Clostridium botulinum and Staphylococcus aureus • Used in meat and fish preservation • For the retention of red colour of meat. vii) Propionic acid & propionates Sodium & Calcium propionates • Used to prevent mould in sliced bread • For preservation of cheese
- 20. viii) Salicylic acid& Salicylates • Used to preserve fruits and vegetables ix) Antioxidants Used to prevent oxidation of fats and oils which causes rancidity (Development of unpleasant odour) Egs Butylated Hydroxy Anisole (BHA) Butylated Hydroxy Toluene(BHT)
- 21. x) Antibiotics- Aureomycin(Chlortetracyclins), Terramycin (Oxytetracyclins), Chloromycetin (Chloramphenicol) Inhibit protein synthesis Used to length storage time at chilling temperatures – meat, fish, poultry etc.
- 22. 3. Preservation byuse of low temperature • Microbial growth and enzyme reaction are retarded in foods stored at low temperature. a) Cellar storage (Temperature about 15 ° C) • Storage in cellars(underground rooms) slows down the decomposition. • Can be stored for limited periods during winter months. Eg - Root crops Potato Onion Apple Cabbage
- 23. b) Refrigeration orChilling treatment ( Temperature 0 °C – 5 ° C) • Retard the growth and metabolic activities of microbes • Can be stored for a few days • Fruits • Vegetables • Meat • Poultry • Milk • Fish • Egg • Prepared Food.
- 24. c) Freezing (Temperature,- 18 °C to – 40 ° C) • The growth of microbes and enzyme activity are reduced to the minimum. • Can be stored for long periods – a few weeks to months . • Before freezing, vegetables are given blanching (mild heat treatment, above 80 °C)to inactivate the enzymes .
- 25. Quick freezing –at temperatures between -18 °C to – 34 ° C for 30 minutes or less • Maintain the identity and freshness when they are thawed(brought to room temperature) because very small ice crystals are formed during quick freezing. Vegetables Fruits (Strawberry) Meat Sea foods Mushrooms etc.
- 26. 4. Preservation byuse of high temperature • Most reliable and safest method • High heat coagulate proteins and inactivate the enzymes of microbes → destruction a)Pasteurisation (Temperature below 100 °C) • Brief exposures to moderately high temperatures to reduce the number of viable microorganisms and kill the pathogenic microorganisms.
- 27. • Used wheredrastic heat treatment may cause undesirable changes in the food • Usually supplemented by other methods – sudden cooling and keeping in refrigeration to prolong shelf life.
- 28. i) High TemperatureShort Time (HTST) Method Milk is heated to 72 °C for 15 seconds and rapidly cooled to 10 °C and kept under refrigerated conditions – inhibits the growth of organisms that may have survived. ii) Low Temperature Long Time (LTLT) Method Milk is heated to 62.8 °C for 30 minutes followed by sudden cooling to 10 °C and kept under refrigerated conditions.
- 29. USES OF PASTEURISATION •Preservation of milk and other dairy products • Beer • Fruit juices • Aerated drinks • Dried fruits –Raisins , Apricots, Dates etc. • Grape wine –pasteurized at 81 °C - 85 °C for 1 minute • Grape juice at 76.7 °C for 30 minutes.
- 30. b)Boiling( Temperature 100°C) • Kills the vegetative cells and spores of yeasts and moulds • Kills only the vegetative cells of bacteria. • Cooked food can be preserved from 12 – 24 hrs at room temperature, esp. on winter months. • Cooking of rice • Vegetables • Milk • Meat • Fish
- 31. c)Canning( Temperature above100 °C; Steam under pressure , 121 °C) Discovered by Francois Nicolas Appert (1809) – Appertization. • Most widely used method • Exposure to high temperature for longer periods – kill endospore -forming bacteria. Steam under pressure(Pressure cooker or autoclave) • Most effective method – kills vegetative cells and spores • Heating to high temperature is followed by rapid cooling
- 32. Canning Process i) Cleaning– Select high quality materials and clean –fresh vegetables, fruits, meat etc. ii) Blanching – in hot water or in steam – kills microbes, fixes natural colour, removes air within product and inactivates enzymes. iii) Filling of cans or jars –Hot food is filled into cans (tin cans →made of tin –coated steel, glass containers, flexible pouches, plastic bags, Aluminium cans → used only for products that do not require high vacuum or high temperature processing such as beer, frozen fruits and juice concentrates, cheese etc.)
- 33. iv) Autoclaving • Cans→ steam under pressure • Duration depends on load - more time for heavily loaded. • Non-acid foods →116 -121 °C at lbs/psi pressure for 1 -2 hours. • Meat require more time • Acid foods require only immersion of cans in boiling water.
- 34. v) Cooling • Autoclavedcans are immediately cooled → prevent undesirable changes in texture and flavour due to overcooking. 5. Preservation of food by creating anaerobic conditions. Prevent the growth of aerobes a) Vacuum filling- food materials are packed in impermeable plastic material and the air is sucked out to create vacuum. Used for Nuts- to reduce loss of flavour due to oxidation Meat Cheese etc.
- 35. b) Modified atmospherepackaging • Enclosure of food in a package in which the atmosphere is changed by altering the proportions of Carbon dioxide, Oxygen, Nitrogen ,water vapour and trace gases. • Retards microbial and biochemical activity. • Salad crops are packaged in sealed bags with an atmosphere modified to reduce Oxygen concentration and increase carbon dioxide concentration. • Can be used to increase the shelf life of bacon, red meat, poultry, vegetables etc.
- 36. 6. Food Preservationby radiation (Cold sterilization – the product is not heated) • Approved only in a very limited way. • Mainly used for spices and condiments • Reduces the number of microbes and insects – replaces the chemicals used for this purpose. • Inhibits sprouting in Potato, Onion, Garlic etc. • Delays ripening in Banana, Avocado, Papaya, Guava etc. • UV rays are the most widely used – for the treatment of water for beverage and knives for slicing bread, sanitizing eating utensils etc. • Gamma rays are also used. • Irradiated food materials – meat, fish, poultry etc. can be stored at room temperature without spoilage.
- 37. 7. Use ofanti-sprouting chemicals • Increases shelf life in root crops , tubers etc. – Potato, Carrot, Onion etc. E.g. Maleic hydrazide is used as an anti- sprouting agent for Potato.
- 38.