Microorganisms and Food

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Microorganisms and Food from AS Level Biology OCR Unit 2
gordonbrad
Flashcards by gordonbrad, updated more than 1 year ago
gordonbrad
Created by gordonbrad over 8 years ago
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Question Answer
Microorganisms can be used to make food e.g. bread, wine, cheese and yoghurt.
Bread is made by mixing yeast, sugar, flour and water. The yeast turn the sugar into ethanol and CO2 which makes the bread rise.
Wine is made by adding yeast to grape juice. The yeast turn the sugar in the grape juice into ethanol and CO2.
Cheese is made by adding bacteria to milk. The bacteria turn the sugar in the milk into lactic acid which causes the milk to curdle. Then an enzyme turns the curdled milk to curds and whey. The curds are separated and ripened into cheese.
Yoghurt is made my adding bacteria to milk. The bacteria turns the milk into lactic acid, causing the milk to clot and thicken, creating yoghurt.
Advantages to Using Microorganisms to Make Food 1) populations of microogransisms can grow rapidly under the correct conditions so food can be produced quickly. 2) microoganisms can grow on a variety of cheap materials. 3) their environment can be artificially and easily controlled. 4) some of the food made can last longer in storage than the raw product e.g. cheese and milk.
Disadvantages to Using Microorganisms to Make Food 1) high risk of contamination - the conditions to grow the helpful microorganisms may also be desirable to the harmful ones. This could cause food poisoning. 2) Small changes in the environment (like temperature or pH) can kill the microoganism.
Food spoilage can be caused by the growth of unwanted microorganisms as they break down the food and contaminate it with waste products. To prevent food spoilage is to kill the microorganism or depriving them of the conditions they need to grow.
1) salting - adding salt inhibits the growth of microorganisms by interfering with their ability to absorb water. Used on meats and tinned foods. 2) Sugar - adding sugar inhibits the growth of the microorganism by interfering with their ability to absorb water. Used on jams. 3) Freezing - keeps food below -18°C, slowing down reactions taking place in the microorganism and freezing the water in the food. 4) Pickling - the low pH in vinegar reduces enzyme activity so it inhibits their growth. Used on onions. 5) Heat - high temperatures kill any microorganisms. 6) Irradiation - exposing foods to radiation e.g. x-rays and gamma rays kills any microorganisms present and extends shelf-life.
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