Microorganisms, enzymes and signs of food spoilage GapFill

Microorganisms are tiny organisms which cannot be seen with a naked eye – they include bacteria, mould and fungi (e.g. yeast).

All microorganisms require certain conditions to be able to live and reproduce. In addition to food itself, these conditions include:

• Warmth – most microorganisms are only able to reproduce at temperatures between 5 and  377510063 ºC; this range is known as the  thermal dumpthermo-disposaltemperature dungeontemperature danger zone, as that’s when microorganisms can grow the fastest and cause food spoilage or even food poisoning.
•  AridityWater activityDrynessMoisture – like all other live organisms, microorganisms need water to be able to carry out the basic biological processes that allow them to live; this means that lack of water will cause most of them to either form spores (inactive forms which allow them to survive even the most unfriendly conditions), or to die.
• Specific pH – most microorganisms will grow the fastest at  highacidicneutralalkaline pH; this means that adding acid (lowering pH) or alkali (increasing pH) will prevent most of them from multiplying.
• Time – all living organisms need time to grow. For example, bacteria multiply through  metastasisbinary fusionmutationbinary fission, which means every cell copies and duplicates itself. This duplication can happen every 20 minutes, which means that from only one cell, we can obtain two cells after 20 minutes, four cells after 40 minutes, eight cells after 60 minutes, and so on.
• Oxygen – most microorganisms also require oxygen to be able to survive – these are called  aerobicoxygenatedoxygenicanaerobic organisms. However, some microorganisms are able to live without oxygen – these are called anaerobes. Anaerobic microorganisms can grow and develop even after food has been vacuum packed, so it is important to always check whether all food looks and smells as it should.

Microorganisms can cause food spoilage e.g. moulds create a green, white or black furry coating on bread, fruit and vegetables, while bacteria can spoil moist foods such as raw chicken (it will smell foul and become slimy). Yeast may cause apple juice to become fizzy and  saltysweetsourbitter.Some foods are higher risk than others, such as ready to eat moist foods and foods that are higher in protein (because they promote the growth of pathogenic bacteria and do not usually require further cooking),

Food spoilage can also be caused by enzymes. Enzymes are biological  producersanalystscatalystsenhancers usually made from protein. This means that they can  speed upinhibitdecreasehamper the tempo of various chemical reactions within the cells. Enzymes can cause vegetables and fruits to darken in colour (this is called enzymatic browning) and become mushy, so it is important to prevent them from acting. As enzymes are made from protein, one can stop enzymatic action and, therefore, enzymic browning by: storing food at very low temperatures (as enzymes are less active and generally work more slowly then), blanching or cooking (as high heat will  stircarameliseemulsifydenature the protein) before freezing, removing oxygen from the air (most enzymes must react with oxygen to be able to cause any damage) and also using acids; for example, squeezing lemon juice.

The most common cause of food poisoning in England is  ListeriaCampylobacterStaphylococcus aureusRubella. This is an S-shaped bacteria that occurs most commonly in raw poultry (especially chicken), red meat, unpasteurised milk and untreated water. The first symptoms appear from two to five days after consumption of contaminated food, and include diarrhoea (sometimes with blood in it), nausea and vomiting, and sometimes fever.

Another commonly occurring pathogen is salmonella. It is usually associated with  raw eggsdirty handsraw vegetablescooked eggs and poultry, but it can also be found in raw meat and unpasteurised milk. The symptoms appear between 6 and 72 hours from the time of consumption, and include stomach cramps, severe diarrhoea, cold and chills, and vomiting. The infection is especially dangerous to newborns and small children, and the elderly, as it can quickly cause dehydration.

 E. coliClostridiumListeriaStaphylococcus aureus is a type of bacteria that usually lives in the human digestive tract. It can be transferred to the food through dirty hands – for example, if you forget to wash your hands after using the toilet. However, it can also be found in raw meat (where it has been transferred during butchering from the animal’s intestines), vegetables and salads (especially if these are washed with dirty water, or fertilised with manure), and unpasteurised milk. The symptoms appear between two and five days from consumption, and could include severe stomach cramps, watery or bloody diarrhoea, and sometimes vomiting.

Finally, staphylococcus aureus is a bacterium often found in  rawpre-packagedcoldready-to-eat foods made by hand, such as sandwiches, and cooked meats. It can be carried in people's noses and throats and on their skin, and is therefore transmitted through touch, coughing or sneezing. Symptoms can develop within 30 minutes, or in up to 8 hours, and usually last no longer than a day. They include vomiting, diarrhoea and abdominal pain.