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Methods of food preservation
- 1. FOOD PRESERVATION • What is food preservation? Retaining food over a period of time without being contaminated by pathogenic organisms or chemicals and without losing its colour, texture, flavour and nutritious value.
- 2. Advantages: • Increases the shelf life of food • Retain the quality of food – colour, • Texture, flavour & nutrition value • Increases food supply • Adds variety to the food • Decreases wastage of food
- 3. GENERAL PRINCIPLES OF PRESERVATION • To destroy or inactivate micro-organisms. • To prevent the re-entry of new microbes by sealing food. • To maintain the nutritive value, colour, flavour, texture of the food as far as possible.
- 4. METHODS OF FOOD PRESERVATION 1.HEAT PROCESSING 2.DEHYDRATION 3.CHEMICAL PRESERVATION 4.OIL AND SPICES 5.CANNING 6.PASTEURIZATION
- 5. 1.HEAT PROCESSING • All types of spoilage agents are destroyed when subjected to high temperature • Temperature raised to temp with spoilage agents(enzymes, bacteria) can no longer survive • The product is then sterilized airtight containers.
- 6. 2.DEHYDRATION • Process of removing the moisture from product(drying) • Once moisture is removed from products it can it can render growth of spoiling agents • Eg sun drying
- 7. 3.CHEMICAL PRESERVATION • Uses high concentration of salt, sugar and acids. • Salt used as preservative to prevent bacterial growth in vegetables, fruits etc. • Strong acidic medium like vinegar, lemon juice
- 8. 4.OIL AND SPICES • Oil and spices along with salt and sugar are used,they resist the activity of microbes in food and improves flavor of food
- 9. 5.CANNING • Preservation of food in a sealed containers,usually after the application of heat,through steam under pressure • The product is sterilized at 135°C to 172°C for few seconds and sealed in sealed container • Eg.Fruit juices,sauces • Relatively long shelf-life
- 10. 6.PASTEURIZATION • Used on large scale to protect milk against bacterial infection • Milk is heated to min 62°C for 30 minutes, then milk is heated to 70°C for 15 seconds • Milk is sterilized by boiling for a period of time.
- 11. PLATE FREEZING • Food packed between flat, hollow refrigerated metal plates. • Press tightly on the food and reduce any air gaps. • Used for many bulky products • ideal for freezing large blocks of product, but cannot easily freeze irregular shaped items • The plates may be horizontal or vertical
- 12. PLATE FREEZER • Classified into 3 types 1. Batch type 2. Semiautomatic type 3. Automatic type
- 13. Freezing Methods • Quick freezing is done by using one or more of the following ways: • Air blast freezing • Contact freezing • Immersion freezing
- 14. 1.Immersion Freezing • Food products dipped in low temp liquids • Non toxic, does not affect flavor • Produce thin ice coating on product surface preventing food products from dehydrating during storage
- 15. Immersion freezer • The immersion freezer consists of a tank with a cooled freezing media, such as sodium chloride, calcium chloride and mixtures of salt and sugar. • The product is immersed in this solution or sprayed • fast temperature reduction through direct heat exchange.
- 16. 2.AIR BLAST FREEZER • Either still air or forced air is used. • Air is recirculated over food at between 30ºC and 40ºC at a velocity of 1.5–6.0 m/s. • In batch equipment, food is stacked on trays in rooms or cabinets.
- 17. 3.Contact freezing • Product is freezed when metal surface cooled by refrigerant like ammonia or cold brine comes in direct contact with product.