Food Protection Vs Bacterial food infections

Sanjeet Kumar

sanjee.biotech@gmail.com

Food protection and food preservation have one aim in common they are intended to prevent contamination and spoilage of foods by bacterial infections. Many of the methods of food protection and preservation used today are of ancient origin. Having an understanding of food microbiology is important for food protection and preservation practice. Food protection methods are measures taken to protect food from being contaminated by any agent. All food must be protected at all times during storage and preparation from the following contaminants:

Ø Any water that is not known to be safe, including overhead leaks and drips

Ø Dirty hands

Ø Coughing and sneezing

Ø Dust and soot

Ø Flies, rodents and other vermin

Ø Insecticides and other chemicals

Ø Unclean utensils and work surfaces

These factors either affect the food directly to make it unsafe or, like coughs and sneezes or insects, contaminate the food with bacteria. The most important way of preventing contamination is by adopting good food handlers’ hygiene. This is the term for a group of practices that should be followed at all times by anyone handling food at any stage of the food supply process. Food handlers’ hygiene in retail and commercial premises where food and drink is sold to customers is of critical importance. The importance of promoting good food handlers’ hygiene is:

v  To prevent food contamination and spread of disease caused by bacterial food infections.

v  To ensure the good health of people eating the food.

v  To protect the health of the food handler.

There are other general principles for preventing food contamination:

• All water used in food preparation should be wholesome.
• All dishes, glasses and utensils must be kept clean by regular washing in clean water, and clean utensils should be kept covered.
• All surfaces that come into contact with food should be meticulously clean.
• Food storage, preparation and serving areas should be free of pets, rats, mice and insects.
• Food should be covered, and kept separate from chemicals and poisons.
• Cloths that come into contact with dishes and utensils, and that are used to cover food, need to be changed daily and boiled before use.

Food is particularly vulnerable to contamination while it is being prepared for eating. It is important to remember food handlers’ hygiene and to ensure that all surfaces and utensils are clean. Foods intended to be eaten raw, such as fruit and some vegetables, must be washed carefully in clean, safe water. Food that is to be cooked must be cooked thoroughly to kill all pathogenic microorganisms. All parts of the food must reach a temperature of at least 70^oC. Food preservation includes a variety of techniques that allow food to be kept for extended periods of time without losing nutritional quality and avoiding the growth of unwanted microorganisms. There are three basic objectives for the preservation of foods:

• Prevention of contamination of food from damaging agents.
• Delay or prevention of growth of microorganisms in the food.
• Delay of enzymic spoilage, i.e. self-decomposition of the food by naturally occurring enzymes within it.

Technique simply means to prevent contamination of the food by spoilage agents or by contact with them. The word ‘aseptic’ means free from harmful bacteria, viruses etc. The technique requires either using an artificial covering for the food, or keeping its natural protective covering if there is one. Examples of natural coverings are the shells of eggs, fat or skins in animals, and/or the skin or peel of fruits. Leaving the natural covering of the food intact, or applying a clean artificial cover, can prevent microorganisms from entering or dropping on to the food.

Bacteria can be physically removed from food, or their numbers reduced, by techniques like washing, trimming, sieving and filtration. For example, vegetables and fruit should be washed in clean water; any damaged or dirty parts of vegetables should be trimmed off with a clean knife; flour can be sieved to remove any unwanted contaminants. Heat is one of the oldest methods of destroying microorganisms in food processing and preservation. The greatest advance in food hygiene was inadvertently made when humans discovered the advantage of boiling, roasting, baking and other heat treatments of food, hence preserving the food for longer periods. Food is also rendered safe by the application of heat because most pathogenic microorganisms are comparatively heat-sensitive. Some of the methods of heat treatment used for food preservation are discussed below.

Boiling is the process of applying heat to water until the temperature reaches about 100°C. Boiling foods in water cannot completely destroy all microorganisms, but the vegetative cells of bacteria, yeasts and moulds are generally quickly destroyed at temperatures of 100°C or above. Spores of some bacteria are extremely resistant to heat and are not killed at this temperature, although their growth is prevented. For this reason, boiling food can rarely be relied upon to ensure complete destruction of all organisms. However, most pathogens are killed, provided that sufficient exposure time is maintained. Although the spores of Clostridium botulinum, which causes botulism, are extremely heat-resistant, the toxin produced by this organism is readily destroyed by boiling. However, some toxins produced by other bacteria such as staphylococci are not easily inactivated. Thermophilic (heat-loving) organisms may survive the effects of boiling and can cause food spoilage if environmental conditions are favourable for them.

Bacterial destruction by heat is affected by time and temperature variation. The higher the temperature, the more rapid is the destruction. On the other hand, as the temperature is lowered, the time of exposure (holding time) needs to be longer.  Cooking can have some disadvantages. It can damage the food’s appearance, texture and flavour, and may also destroy some important vitamins. Nevertheless, the advantages of cooking outweigh the disadvantages because it inhibits spoilage and possible disease transmission.

Pasteurisation is named after its inventor, Louis Pasteur, a French chemist. Pasteurisation is a process of heat treatment of milk, beer and some other beverages. It requires sufficient holding time to assure the thermal destruction of pathogens and organisms responsible for spoilage, without altering the nutritional value. It involves heating the food to a specific temperature for a specific time and then cooling rapidly.  Pasteurisation kills most but not all of the microorganisms present. It is a very useful method when more rigorous heat treatment could harm the quality of the product, as in the case of milk, and when the aim is to kill only the pathogens that are not very heat-resistant. The temperature applied and the holding time of pasteurisation vary with the equipment available and the type of food product. In milk pasteurisation, the time-temperature combination is selected on the basis of the thermal death time of the most resistant pathogens (TB bacilli) that may be present in raw milk, and the maximum temperature and time at which the taste, palatability and nutritive value of milk are maintained. Normally milk is pasteurised at 62.8°C for at least 30 minutes or at 71.7°C for at least 15 seconds, or, if using ultra-high temperature (UHT), at 135°C for 1–2 seconds. UHT milk is sterilised, meaning all forms of life are destroyed. This extends its storage time but does affect the taste.

Blanching is a mild pre-cooking operation which can reduce the bacterial load on vegetables by 90%. It means the application of boiling water or steam for a short time. It wilts some bulky vegetables and prevents discolouring of others. It cleans peas of the moist and sticky material around them. Blanching vegetables prior to canning, freezing or drying helps to remove soil, insects and microorganisms, and destroys or slows the action of enzymes. It sets the green colour and generally facilitates dicing, peeling and packing.  Canning is one of the most widely used modern methods of processing and preserving food. It involves the careful preparation of food packed into a sealed tin, glass or plastic container which is subjected to defined high temperatures (above 100ºC) for an appropriate period of time, and then cooled. Following the thermal (heat) processing, the sealed container must be cooled immediately to a temperature of about 38ºC to prevent unnecessary adverse effects of heat on the texture, flavour or colour of the food.  The canning method involves the following steps: sterilising the food to be canned, packing it in sterile, air-tight stainless metal, glass or plastic containers, and then hermetically sealing (i.e. with a complete, airtight seal) the containers to prevent contamination during handling and storage. In the heat process, all vegetative bacteria are destroyed and spores cannot grow. Any can that is damaged or swollen should not be used. A swollen, bulging can indicates that gas is being produced on the inside and demonstrates there is microbial activity in the food, so it would not be safe to eat.

Source:http://www.open.edu/openlearnworks/mod/oucontent/view.php?id=196&printable=1