3.4.1.1 Microorganisms and enzymes and 3.4.1.2 The signs of food spoilage GapFill

Microorganisms are tiny organisms which cannot be seen with a naked eye – they include  mushroomsbacteriaspoilerspesticides, 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  63257540 ºC; this range is known as the  temperature dungeoncontingencythermal threattemperature danger zone, as that’s when microorganisms can grow the fastest and cause food spoilage or even food poisoning.
•  Water activityMoistureEvaporationAcidity – 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  eggscellsvacuolesspores (inactive forms which allow them to survive even the most unfriendly conditions), or to die.
• Specific pH – most microorganisms will grow the fastest at  aridacidicneutrallow pH; this means that adding acid (lowering pH) or alkali (increasing pH) will prevent most of them from multiplying.
• Time – microorganisms multiply through  duplicationbinary fusionbinary fissionprimary fusion, which means that every cell can copy and duplicate itself; the 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 – some microorganisms also require oxygen to be able to survive – these are called  comensalesaerobicanaerobicparasites; however, other 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 the food looks and smells as it should.

Microorganisms can cause food spoilage – there tends to be higher risk foods than others, such as ready to eat moist foods and foods that are usually higher in protein (because they promote pathogenic bacteria and do not usually require further cooking), 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  sweetsourfruitymilky.

Food spoilage can also be caused by enzymes. Enzymes are biological  impulsesblockersanalystscatalysts usually made from protein. This means that they can  retardspeed uphinderdecrease 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  denaturecaramelisedissolvedilute 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.