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Preserving Food © ORCA Education Limited 2005 New Words Scientific Principles Food preservation stops food going bad. It prevents or delays spoilage and stops the growth of harmful micro-organisms such as bacteria, yeasts and moulds. To survive and spread, micro-organisms need warmth, food, moisture and time to grow. Preservation changes the environment of the food and therefore prevents the growth of micro-organisms. Enzymes in food also cause deterioration and must be destroyed. In what foods do we use micro-organisms? * © ORCA Education Limited (2005) and suppliers, all rights reserved Why Preserve? Throughout history people have found ways to preserve food, like smoking or sun-drying this fish. Ideally we would eat food fresh. This is not possible as we need food to last for when it is not available fresh. Preserving food has also improved food safety. Preservation lets us buy or collect food when it is plentiful or cheap and eat it out of season. * © ORCA Education Limited (2005) and suppliers, all rights reserved Preservation Methods To preserve food like this fruit we need to remove the conditions microorganisms need to survive and grow. Our choices are: to use high or low temperatures reduce moisture (dehydration) add chemicals to change the acid/alkaline conditions or remove water remove air to deprive micro-organisms of oxygen and prevent further re-entry by sealing it from the outside world irradiation using new technology. * © ORCA Education Limited (2005) and suppliers, all rights reserved The Use of Heat Most bacteria, yeasts, moulds and enzymes are destroyed by heating to 100ºc. The methods include: Canning and bottling where heat sterilization destroys micro-organisms and enzymes and seals to prevent contamination. Pasteurisation which heats food to 72ºc and destroys many but not all micro-organisms. Ultra heat treatment (UHT) where high temperatures are used to destroy all Are tinned foods bacteria e.g milk and fruit juices. different to fresh foods?* © ORCA Education Limited (2005) and suppliers, all rights reserved The Use of Low Temperature Low temperatures remove warmth and moisture that micro-organisms need for growth. Food can be frozen or chilled. Freezing stops the growth of microorganisms, slows down enzyme activity and removes moisture by changing water to ice crystals. Chilling food slows down the rate at which micro-organisms multiply and also slows down enzyme activity. Many prepared foods are cook-freeze or cook-chill where they are cooked and then frozen or quickly chilled. © ORCA Education Limited (2005) and suppliers, all rights reserved Drying Drying or dehydration removes the moisture micro-organisms need for growth and reproduction. This is a very old method of preservation where fruit, vegetables, fish and meat would be sun-dried or oven dried. Today, mechanical methods used are: spray drying for liquids such as milk hot air beds for drying solid food such as meat and pulses. This freeze dryer freezes food quickly then the tiny ice crystals are removed by turning them to steam by heat in a vacuum. © ORCA Education Limited (2005) and suppliers, all rights reserved Chemical Methods Vinegar, salt, sugar and wood smoke have been used for many centuries as preservatives. Vinegar (acetic acid) is used in pickling, the strong acid solution prevents the growth of micro-organisms. Salt (sodium chloride) is used for meat and fish in a solution (brine) or to coat the food. It reduces the moisture content of the food. Sugar is used in jams, canning and dried fruit. In high concentration (60% for jams) it prevents bacteria from growing. Other chemical methods include the addition of antioxidants, sulphur dioxide and nitrites. Apart from the use of sugar what other ways is the jam preserved? * © ORCA Education Limited (2005) and suppliers, all rights reserved Removal of Air Canning and bottling use air removal to preserve as well as sterilise. Removal of air is also used in: Vacuum packing where all air is removed from the package. Food is kept in anaerobic conditions (no oxygen) delaying the growth of micro-organisms. Modified atmospheric packaging where most of the oxygen is replaced with carbon dioxide and nitrogen. Either method is often used to extend the shelf life of meats, fish, bacon and cheese. What other example might you often eat that use modified atmospheric packaging. * © ORCA Education Limited (2005) and suppliers, all rights reserved Irradiation Irradiation is the process of passing X rays from radioactive or electron beams through food. It prevents spoilage by destroying micro-organisms. The energy similar to ultraviolet light does not make the food radioactive but irradiated food must be clearly labelled. The purpose of irradiation is; stop vegetables from sprouting destroy parasites in meat e.g. pork allow longer storage e.g. shellfish and strawberries © ORCA Education Limited (2005) and suppliers, all rights reserved delay ripening of fruit e.g. mangoes and bananas destroy insects that may damage cereals, rice, etc. * Strawberries There are several ways to preserve any one kind of food. Strawberries can be preserved by: canning in sugar syrup or fruit juice jamming freezing chilling irradiation. Some methods will retain the qualities of the fresh strawberry in flavour, texture, colour, appearance and nutritional value, while others will not.* © ORCA Education Limited (2005) and suppliers, all rights reserved Changes to Food How would the characteristics and nutritional value of food like this be changed by preservation? Irradiation of the vegetables will lead to loss of vitamins A,C,E and K. If the fruit or maize are canned the texture and appearance will change but the nutritional value will remain. Drying the apple will concentrate flavour, reduce size and weight and may increase sugar or salt content. Jamming will add flavour and energy value to the strawberries. Sterilisation would change the colour and taste of the milk. * © ORCA Education Limited (2005) and suppliers, all rights reserved Vocabulary Some words or terms to learn spoilage preservation enzymes irradiation pasteurisation antioxidants shelf life parasites © ORCA Education Limited (2005) and suppliers, all rights reserved micro-organisms dehydration sterilization UHT cook freeze cook chilled freeze drying pickling vacuum packing modified atmospheric packaging. * The Task You can enter here a task for your students. © ORCA Education Limited (2005) and suppliers, all rights reserved End End Show Acknowledgements All images used in these presentations are the property of their owners, ORCA Education Limited and suppliers inc. Hemera Images, Jupiter Media Corp. and Animation Factory All rights are reserved. The Licence agreement applies to all elements of these presentations. ORCA.VT is a trademark of ORCA Education Limited Microsoft Agent is the property of Microsoft Corporation, Redmond WA. ORCA Education Limited are licensed distributors of Microsoft Agent technology Licence 276899. The Microsoft Agent Technology elements including Peedy character may not be distributed beyond the constraints of this product licence Microsoft Agent characters Susan and Tom are packaged with this product as part of the Vox Proxy development tools used by ORCA Education. They are not for resale or distribution beyond their use in these products © ORCA Education Limited (2005) and suppliers, all rights reserved