Preservation of Food. H4.2: Applies principles of food preservation to extend the life of food and maintain safety.

Transcription

1 Preservation of Food H4.2: Applies principles of food preservation to extend the life of food and maintain safety.

2 Syllabus Link:

3 What is Food Preservation? Food Preservation is the process of treating and handling food to stop or slow down food spoilage, thus, allowing the food to last longer. Unless special methods are used to preserve foods, the the majority of foods are quick to decompose or rot as a result of micro-organisms and enzymes.

4 Reasons for Preserving Foods S - Safety A - Acceptability A - Availability N - Nutritive Value E - Economic Viability

5 Reasons for Preserving Foods Safety - Ensures food is safe and free from harmful micro-organisms which can cause illness. Acceptability - Keep foods in a state acceptable for the consumer and reduces wastage. Nutritive Value - Retain the nutritive value of the food. Availability - Make perishable foods available all year round which provides for greater diet variety. Economic Viability - Achieve economic viability for food producers by reducing seasonal fluctuations in availability.

6 Causes of Food Deterioration and Spoilage

7 Causes of Food Deterioration and Spoilage Spoilage of food is caused by one or more of the following factors; M - Microbial Contamination (mould, yeast and bacteria) E - Enzymatic Activity E - Environmental Factors (Infestation, oxygen, light and water)

8 Causes of Food Deterioration and Spoilage 1. Microbial Contamination Micro-organisms such as; yeasts, viruses, moulds and bacteria cause foods to spoil. Example; mould on old bread, sliminess on ageing meat. Micro-organisms may be pathogenic, meaning that they have the potential to make a consumer very ill and, thus, need to be controlled. Micro-organisms prefer warm, moist conditions with a neutral ph. When these conditions are favourable, they begin to multiple.

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10 As micro-organisms grow, they pass through a series of phases. PHASE 1 - LAG PHASE This is the time required for the bacteria to become adjusted to the new environment. The greater the number of micro-organisms present - the shorter the lag time. PHASE 2 - LOGARITHMIC PHASE The bacteria cells grow and multiple because they have adjusted to the environment. PHASE 3 - DEATH PHASE During this phase, the food needed by the bacteria is usually all gone and the bacteria die of starvation.

11 Especially important in food preservation is the lengthening of the lag phase of micro-organisms as much as possible. This can be accomplished in different ways; 1. Limiting the number of micro-organism will reduce the amount of contamination. The fewer micro-organisms present - the longer the lag time. This can be achieved by avoiding unclean containers, equipment, or utensils used in food preparation. 2. The micro-organisms will take longer to begin multiplying in an unfavourable environment. Such an environment can be produced by changing the moisture, temperature or ph level. 3. Putting the food through processes such as heating to high temperatures or irradiation actually damages the micro-organisms

12 The time it takes for a single cell to divide and grow into two new cells is called the Generation Time. The time shortens as the conditions become favourable. For example; if the food is chilled, the generation time will lengthen If the conditions for growth are good, a single bacterium can reproduce every 20 minutes.

13 The spoilage of food caused by micro-organisms will be prevented only if all the spoilage organisms are killed (or removed) and re - contamination is prevented Stopping the multiplication of micro-organisms does not necessarily prevent the decomposition of a food. For example; freezing - micro-organisms remain dormant. Minimising cross-contamination is crucial as it ensures that food remains safe. Cross-contamination is the transfer of microbes to food via other items. All foods spoil, however, some spoil faster than others. Perishable foods spoil faster than other foods and are more likely to cause food poisoning.

14 Chemical Preservatives used to remove micro-organisms

15 Causes of Food Deterioration and Spoilage 2. Enzymatic Activity: An enzyme is a substance produced by a living organism. Enzymes are found in meat, fruits and vegetables. Enzymes do not affect the safety of the food if consumed. Enzymes cause fruits and vegetables to over-ripen once harvested and results in loss of turgor due to tissue decomposition.

16 Causes of Food Deterioration and Spoilage 3. Environmental Factors: Organisms such as insects and rodents can cause spoilage of food, such as weevils in flour and rodents transmitting bacteria. Washing may be dangerous if the water is contaminated and adds spoilage organisms. Exposure to oxygen can also encourage microbial growth and speed up enzymatic browning.

17 Principles behind Food Preservation Techniques

18 Principles behind Food Preservation Techniques

19 Principles behind Food Preservation Techniques T - Temperature Control R - Restriction of Moisture E - Exclusion of Air P - ph

20 1. Temperature Control Cooking a food by heating is the simplest and most commonly used method of food preservation. As food is cooked, two important events occur; - Enzymic reaction rates begin to slow. - Micro-organisms are killed when temperatures reach above 60 degrees celsius. - Temperatures above 100 degrees celsius destroys all enzymes and micro-organisms. However, some spore-forming micro-organisms, such as; Clostridium Botulinum can survive at 100 degrees celsius for up to 5 hours. In addition, the higher the acidity of a particular food is, the less time and the lower the temperature it will take to kill any bacteria present. Cooling of the food after cooking is also another important factor in preventing the growth of bacteria. If the food is not eaten hot and is allowed to cool slowly, it can make a person ill.

21 2. Restriction of Moisture Processes which remove moisture from food, such as dehydration and evaporation, are effective in preventing the actions of both enzymes and micro-organisms. This is because both enzymes and micro-organisms need clean, liquid water to survive. Enzymes can still be active in freezing conditions, but their activity occurs very slowly - this is the reason why foods cannot be stored in the freezer indefinitely.

22 3. Exclusion of Air Most microbes require oxygen to be active. By removing air from around the food, the environment becomes unfavourable and microbes become dormant. Some bacteria are anaerobic and care must be taken with processing and packaging options as food poisoning may result. Manufacturers exclude air from packaging such as cans and bottles through a process known as vacuum packing. This is a process in which the air in the headspace is removed and a vacuum is put in its place.

23 4. ph Adding acids to foods can minimise spoilage by denaturing enzymes and destroying microorganisms. Additives, in the form of chemical preservatives, food acids and smoke can be used to destroy micro-organisms. Tomato salsa, jam and pickles are a few of the foods eaten daily that use chemicals to inhibit microbial growth.

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25 1. Many manufactured food producers apply a variety of the principles of preservation to ensure the stable shelf-life of their products. Suggest which principles of preservation are being used when the following foods are manufactured. a) Bottled Jam b) Bacon and Salami c) Pasteurised Milk d) Beef Jerky e) Canned Fruit