How are microorganisms used to make food, and what jobs do enzymes do in food?
Micro-organisms and food production: the useful roles of bacteria, yeast and mould in making bread, yoghurt, cheese and other foods, fermentation, and the action of enzymes in food (ripening and enzymic browning).
A focused answer on micro-organisms and food production for Eduqas GCSE Food Preparation and Nutrition (C560), covering the useful roles of bacteria, yeast and mould in making bread, yoghurt and cheese, fermentation, and the action of enzymes in ripening and enzymic browning.
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What this dot point is asking
Eduqas wants you to know the useful side of micro-organisms: how bacteria, yeast and mould make bread, yoghurt and cheese through fermentation, and what enzymes do in food (ripening and enzymic browning). This is the counterpart to food poisoning, where micro-organisms are harmful.
Useful micro-organisms: bacteria, yeast and mould
Fermentation in bread, yoghurt and cheese
- Bread. Yeast, given warmth, moisture, food and time, ferments the sugar in the dough to produce carbon dioxide, which is trapped by the gluten so the dough rises; baking kills the yeast and sets the loaf.
- Yoghurt. Helpful bacteria are added to warm milk and ferment the lactose into lactic acid; the acid thickens the milk and gives yoghurt its tangy flavour and set texture.
- Cheese. Bacteria sour the milk by making lactic acid, and the enzyme rennet coagulates the milk proteins to form curds, which are separated from the whey, pressed and ripened, sometimes with moulds as in blue cheese.
Enzymes in food
Enzymic browning affects apples, pears, bananas and potatoes. It can be slowed by stopping the enzyme or excluding oxygen: coat the cut surface with acid (lemon juice), cover the food or keep it under water to keep out air, or blanch (briefly heat) it to destroy the enzyme. Enzymes also continue to ripen and then over-ripen fruit, which is one cause of spoilage.
Try this
Q1. Name the acid that bacteria make from lactose when yoghurt is produced. [1 mark]
- Cue. Lactic acid.
Q2. Give one way to slow enzymic browning on a cut apple. [1 mark]
- Cue. Any one of: coat with lemon juice (acid), cover or submerge to exclude air, or blanch to destroy the enzyme.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20186 marksExplain how micro-organisms are used to make bread, yoghurt and cheese.Show worked answer →
A 6-mark extended-response question covering three useful uses.
Bread uses yeast, a single-celled fungus. Given warmth, moisture, food and time, the yeast ferments the sugar in the dough to produce carbon dioxide gas, which is trapped by the gluten and makes the dough rise. Baking kills the yeast and sets the structure.
Yoghurt uses bacteria. Helpful bacteria are added to warm milk and ferment the lactose (milk sugar) into lactic acid; the acid thickens the milk and gives yoghurt its tangy flavour and set texture.
Cheese uses bacteria and an enzyme (rennet). Bacteria sour the milk by making lactic acid, and rennet coagulates the milk proteins to form curds, which are separated from the whey, pressed and ripened, sometimes with moulds (as in blue cheese).
Top-band answers (5 to 6 marks) name the micro-organism for each food and explain what it does (carbon dioxide for bread, lactic acid for yoghurt, souring and curdling for cheese).
Eduqas 20204 marksExplain what enzymic browning is and give one way to slow it down.Show worked answer →
A 4-mark structured question on enzyme action.
Enzymic browning is when cut or damaged fruit and vegetables (such as apples, pears, bananas and potatoes) turn brown. Enzymes in the food react with oxygen in the air at the cut surface, producing brown compounds.
It can be slowed by limiting the oxygen or stopping the enzyme: coat the cut surface with acid (lemon juice), cover the food or keep it under water to keep out air, or blanch (briefly heat) the food to destroy the enzyme. Cooling also slows the reaction.
Markers reward explaining the enzyme-plus-oxygen reaction at the cut surface and one valid way to slow it (acid, exclude air, or blanch).
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Sources & how we know this
- WJEC Eduqas GCSE Food Preparation and Nutrition specification (C560) — WJEC Eduqas (2016)