Food Flashcards
Describe the key steps in the production of cheese, bread and beer.
Describe the key features of food poisoning caused by intoxication and the key features of food poisoning caused by infection.
Describe the key features of enterotoxins and neurotoxins.
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Cheese production
6 points
- Depends principally on bacterial growth in milk
- A fermented dairy product - others include yoghurt
- Bacteria ferment sugar (lactose) to produce acid (lactic acid)
- pH drops and the protein (casein) precipitates
- Solid matter (curds) separated from liquid (whey) and pressed to form cheese
- Flavours added by further microbial growth
Cheese production
Starter culture
3 points
- Lactic acid bacteria (LAB)
- LAB include members of the genera Lactococcus, Lactobacillus, Streptococcus, Leuconostoc
- Different cheeses use different starter cultures: affect rate of curd formation, end products – influence taste
Cheese production
Ripening
4 points
- Microbes ferment residual lactose, protein or fat to produce products of particular taste
- Brevibacterium linens (Limburger) and Penicillium camemberti (Brie, Camembert) – grows on surface to give aromatic flavour
- Penicillium roqueforti (Roquefort, Stilton, Danish Blue) – grows in natural cavities to give green/blue colour
- Propionibacterium shermanii (Swiss Emmental) – gives flavour and holes/eyes in the cheese
Bread production
6 points
- Depends on yeast (Saccharomyces cerevisiae) growth
- Amylase enzymes in flour break down the starch in flour to glucose
- Yeast metabolises glucose to CO2 and H2O aerobically (plus some ethanol anaerobically)
- CO2 causes the dough to rise (leavening)
- Baking makes the volatile ethanol burn off and sets bread with holes in it
- Adding other yeasts and bacteria can produce specific flavours (S. exiguus and Lactobacillus sp. – sour dough bread)
Bread production step by step
- Prepare dough ->
- add yeast ->
- kneed (good mixing and aerobic conditions) ->
- allow dough to rise due to CO2 production (leavening) ->
- Bake
Beer production
5 points
- Depends on growth of yeasts
- Cereals (barley) allowed to germinate (malting) – produces enzymes to degrade starch
- Malted cereals “mashed” with warm water – enzymes degrade starch to maltose and glucose
- Clear liquid (wort) removed and boiled with hops
- After cooling yeast is added to ferment sugars to alcohol
Beer production
Bottom fermentation
4 points
- Saccharomyces carlsbergensis
- Yeast settles to bottom of fermentation vat
- Produces lager
- Fermentation at 6-12 ºC in 8-14 days. Stored at –1 ºC for several weeks before packaging
Beer production
Top fermentation
5 points
- Saccharomyces cerevisiae
- Yeast does not settle
- Produces beer
- Fermentation at 14-23 ºC in 5-7 days. Stored at 4-8 ºC
Beer production step by step
7 points
- Malt grain ->
- Mash ->
- Boil wort with hops ->
- Add yeast S. cerevisiae, S. carlsbergensis ->
- ferment
- Store
- package
Food Poisoning
potential cause
Microorganisms – bacteria, viruses, fungi
Food Poisoning
Gastroenteritis (common symptom of food poisoning)
- Abdominal pain
- Diarrhoea
- Vomiting
- Fever
- symptoms may be due to: Intoxications
Infections
Food Poisoning
Intoxications
4 points
- Caused by toxin released by bacteria growing on food
- Ingestion of live bacteria not required
- Toxins are exotoxins
- Enterotoxins or neurotoxins produced by bacteria
Food Poisoning
Intoxications
Enterotoxin (causes gastroenteritis)
3 points
- Cause H2O and Na+ to pass from enterocytes (cells lining gut) into gut lumen (normally reverse) leading to diarrhoea
- Also may stimulate vomit receptors in gut which send impulses to the vomit centre in the brain resulting in vomiting
- Toxin remains in gut
Food Poisoning
Intoxications
Neurotoxin
3 points
- Passes through the lining of the gut
- Enters blood stream and transported to all regions of body
- Binds to nerve endings in tissues causing paralysis
