5a) Food Production - Micro organisms (5.5-5.8)

Edexcel IGCSE Biology

5.5 ROLE OF YEAST IN PRODUCTION OF FOOD

5.5 ROLE OF YEAST IN PRODUCTION OF FOOD

5.5 ROLE OF YEAST IN PRODUCTION OF FOOD

Why do you need yeast to make bread?

• fermentation using yeast

• yeast carries out anaerobic respiration and produces CO2 which allows the bread to rise (small air pockets of CO2 trapped inside dough)

how does the yeast carry out anaerobic respiration?

• yeast is mixed with water and flour

• enzymes in yeast break down the starch in the flour into sugars

• sugars are then used for anaerobic respiration

what is the word equation for anaerobic respiration in yeast?

glucose → carbon dioxide + ethanol + energy

what happens to the ethanol when the bread is baked?

• the ethanol evaporates

• the high temperature of the oven also kills the yeast so it no longer carries out anaerobic respiration

5.7 - ROLE OF BACTERIA IN YOGHURT PRODUCTION

5.7 - ROLE OF BACTERIA IN YOGHURT PRODUCTION

what is the name of the bacterium used in yoghurt production?

lactobacillus

why do you need to pasteurise the milk beforehand?

• to kill any unwanted bacteria in the milk

• prevents contamination

  • contamination could cause competition from other bacteria which would slow production

  • contamination could spoil taste

at what temperature is the lactobacillus added to the milk?

40-45 degrees celsius

what does the lactobacillus do when added to the milk?

• digests milk proteins

• ferments the sugar (lactose) in the milk

  • converts the lactose into lactic acid

  • lactic acid sours the taste and thickens the milk to form yoghurt

  • lactic acid lowers the pH to prevent growth of other micro organisms

what temperature is the yoghurt cooled to in the final stage and why?

• cooled to 5 degrees celsius

• halts the lactobacillus

5.8 - INDUSTRIAL FERMENTER

5.8 INDUSTRIAL FERMENTER

what are industrial fermenters used for?

• grow large amounts of culture micro organisms

how is pH monitored in an industrial fermenter?

• monitored using a probe

• adjustments to pH made by adding acid/alkali

• optimum pH = optimum environment for particular micro organism being grown

how is temerpature monitored in an industrial fermenter?

• monitored using probes

• optimum temperature = optimum environment for enzymes to increase enzyme activity

• optimum tempertauare maintained using a water jacket

why are aseptic precautions needed in an industrial fermenter?

• cleaned using steam

• prevents chemical contamination

• kills unwanted micro organisms

why are supplies of oxygen needed in an industrial fermenter?

• oxygen is needed for aerobic respiration

why are nutrients needed in an industrial fermenter?

• used in respiration = releases energy for growth

• growth is need to reproduce micro organism

why is agitation needed in an industrial fermenter?

• stirring paddles provide agitation

• ensure theat micro organisms, nutrients, oxygen, temperature and pH are all evenly distributed throughout the fermenter