WJEC Level 3 Certificate in Food Science and Nutrition

The white powdery appearance of this piece of fruit is due to yeast spores Yeasts growing on a piece of fruit Yeast cells ‘budding’ 11 Yeasts decompose foods by the process of fermentation , which breaks down carbohydrates into carbon dioxide gas and alcohol (ethanol). They do this with a variety of enzymes, including zymase, which changes the sugars glucose and fructose into carbon dioxide gas and alcohol (ethanol), as shown in this simplified chemical reaction: C 6 H 12 O 6 2C 2 H 5 OH + 2CO 2 fermentation process Carbohydrate Ethanol Carbon dioxide gas In breadmaking, the aroma in the air when bread is baking is mainly due to the ethanol being evaporated. The life cycle of yeasts Wild yeast spores are found in the air and will settle on foods, especially those that contain sugars, (e.g. the skins of berries, grapes, apples and other fruits) and start to ferment them. The yeasts appear as pale brown colonies on the skin of the decomposing fruit. Under optimum conditions, yeasts reproduce by sending out a small bud from each yeast cell, which enlarge and eventually break away and become separate yeast cells. If conditions are unfavourable for reproduction, yeasts will form spores that germinate once favourable conditions return. Viruses Like micro-organisms, viruses are capable of causing infections but are different for the following reasons. Viruses are extremely small – approximately 100 times smaller than bacteria – and are therefore only visible using a powerful electron microscope. Each virus consists of a nucleic acid molecule inside a coat made of protein. They can only reproduce inside the living cells of a host, i.e. a plant, animal (including humans), bacteria, mould or yeast. When infected, the host cell will rapidly produce thousands of copies of the virus (called contagions – which is why the host is said to be contagious ), which will then be passed on to other hosts; in the case of humans and other animals, through various body fluids such as blood, faeces, saliva, mucus, and the spray produced by sneezing. Norovirus is an extremely contagious virus that can cause an acute form of gastroenteritis (nausea, vomiting, diarrhoea, severe abdominal pain, fever). Only a few norovirus particles will make an individual ill within 12–48 hours of exposure. The illness lasts from one to three days. It can be caught either by direct contact with a contagious person, touching contaminated surfaces then putting unwashed hands into the mouth, or consuming contaminated food or water. If someone has vomited in a public place, such as a restaurant or in a kitchen, it is really important to de-contaminate the area thoroughly to reduce the risk of infecting other people. Electron microscope image of the Norovirus, which is associated with food poisoning Micro-organisms