Methods of food preservation

Transcription

1 Methods of food preservation ACTIVITY 3 CLIL TECHNOLOGY

2 SOME INTERESTING VIDEOS FOOD SPOILAGE BACTERIA GROWTH METHOD OF FOOD PRESERVATION ARE FOOD PRESERVATIVES BAD FOR YOU? STORAGE AND PRESERVATION FOOD

3 Summary Food preservation is necessary to maintain human life. We preserve food for human safety, quality enhancement, convenience, and to maintain an adequate supply. Food preservation will be as important in the future as it was in the past. Controlling microbes and enzymatic activity are the goals of a variety of preservation techniques. If these techniques are not used, physical, chemical, and biological deterioration are possible. The time and method of food storage are other major factors that influence food quality.

4 Food Preservation Methods Heat Cold Drying Packaging Additives Fermentation

5 Heat Heating food products is a technique used to destroy microorganisms and endogenous enzymes. Most microbial growth occurs between C. Heat-loving (thermophilic) microbes grow in the range of C. In order to destroy these microbes, food products must be heated to an internal temperature greater than 82 C. Heat-enduring (thermoduric) bacteria survive temperatures as high as boiling so food is often canned under pressure to provide a temperature above 100 C. Sterilizing food means heating the food to about 115 C and maintaining that temperature for 15 minutes or longer.

6 PASTEURIZATION We have often heard about pasteurized milk packets. In this method food is heated to a high temperature and then quickly cooled. The micro-organisms are not able to withstand the sudden change in temperature and are destroyed. However, some organisms still survive in this method.

7 PASTEUR Louis Pasteur was born in Dole, France on December 27, His family was poor and during his early education he was an average student who enjoyed art and singing. However, when Louis was exposed to Science as a teenager, he knew he had found his calling. In 1838, Louis went to college to become a Science teacher. He earned degrees in Mathematics, Physics, and Chemistry. He then became a Chemistry professor at the University of Strasbourg. While at the University he fell in love with the daughter of the university's rector, Marie Laurent. He and Marie married in They had five children, however, three died young from typhoid fever. It was the deaths of his children that drove Louis to investigate infectious diseases in order to find a cure.

8 STERILIZATION This is done to prevent any spoilage of food items due to microorganism. What does the word sterilization mean? It means free from any living organism. The high temperature used in this method destroys all the micro-organisms in the food. The food items are exposed to high temperature for a longer period than with pasteurization and in some cases under pressure.

9 Cold Refrigeration, or maintaining 0 to 4 C, is useful to slow microbial growth. Freezing is achieved by reducing the temperature to - 18 C or lower, which virtually stops microbial growth.

10 FREEZING

11 Drying Drying - Dehydrating is the removal of moisture to limit microbial and chemical activity. Freeze-drying is the removal of moisture from a frozen food under reduced atmospheric pressure.

12 Irradiation Irradiation is a technique that uses gamma rays or beta particles to bombard and kill microbes and inactivate enzymes. od under reduced atmospheric pressure.

13 Additives The use of additives or chemicals to prevent microbial growth is another preservation technique. Sweetening, or achieving a high sugar content, produces a high osmotic pressure which causes water to be withdrawn from microbes. A 70 percent sugar level is necessary to prevent all microbial growth. Salting produces a high osmotic pressure or low water activity (Aw) and restrains microbial growth. Salt levels of percent are common in salt cured food products. Smoking food products allows formaldehyde and phenolic compounds to settle on the food surface. The compounds inhibit microbial growth. Spicing is a technique used to slow the growth of some microbes.

14 Packaging Vacuum packaging is the removal of most of the oxygen from food products. This prevents aerobic microbial activity and is usually applied during packaging of refrigerated solid foods.

15 CANNING PROCESS OF PRESERVING FOOD BY HEATING AND SEALING IT IN CONTAINERS FOR STORAGE

16 Fermentation Fermenting, also known as souring or pickling, slows bacterial growth. Acids produce a low ph, which restrict microbial growth. Sometimes, desirable microorganisms are allowed to grow in the food. The use of desirable microorganisms to preserve food is called fermentation. Bacteria convert carbohydrates into acids and alcohol.

17 OBJECTIVES After studying this lesson you will be able to: understand the terms food-spoilage and food-storage; categorize the food items of daily use according to their shelf life; define food-preservation and state its importance; discuss general principles of food preservation; know the household methods of preserving food; evaluate the hygiene practiced in handling food stored at home and see how it helps in preventing food spoilage and wastage.

18 Choose the correct answer to complete sentences below: Food spoilage is due to: a) micro-organisms and enzymes b) micro-organisms and excess production c) enzymes and excess production d) all the above

19 Non- perishable food items are those which a) do not spoil at all b) take long time to spoil c) spoil easily d) spoil according to where they are kept

20 Preservation of food means a) to keep food safe b) to retain quality of food c) to prevent decomposition of food d) all the above

21 Shelf life of food is related to a) freshness of food b) quality of food c) decomposition of food d) time limit for which food can be used

22 The main reason for preserving food is to a) improve its color and taste b) increase its shelf life c) make costly food available d) change its texture

23 Fill in the blanks using appropriate words. (1) Pasteurization is an example of preservation by... (2) Refrigeration reduces the activity of... and... (3) Dehydration is based on the principle of removal of...

24 WHAT YOU HAVE LEARNT 1. Food preservation adds variety in the diet, increases shelf life and helps to avoid wastage of food. 2. You can preserve fruits and vegetables by using salt, sugar, oil, spices by dehydration. 3. Microorganisms, presence of enzymes and insects are causes of food spoilage. 4. Salt, sugar and oil are natural preservatives used for preparation of pickles, jams and squashes. 5. Sodium benzoate, potassium metabisulphite, citric acid are chemical preservatives used in products like tomato ketchup, potato chips and jams.