L11- Microbes and food Flashcards
What is Rennet?
A complex of enzymes made in stomachs of ruminants which is used in the production of most cheeses. It’s main component is chymosin.
What’s chymosin?
Main component of Rennet. It’s a protease enzyme that curdles the casein in milk. (by removing surface glycopeptides from the soluble casein micelles in milk).
What’s paracasein?
The treated casein. Paracasein removes charged peptide side chains from K-casein which causes coaggulation in the presence of calcium and –> curds
Why does the charge have to be removed from the casein?
The surface charge around casein micelles separates them.
Which conditions does Rennet work best in?
Acidic conditions. So lactobacilli (bacteria) added first which acidifies it.
What is 90% of hard cheese made using?
Recombinant calf chymosin from Aspergillus niger. (only calves naturally produce chymosin)
What’s Rennet used to separate out in cheese?
Curds and whey
What are the main stages of making cheese?
- precuring at warm temp. (lactobacilli acidifies)
- Coagulation by Rennet
- Separation of the whey
- Compression of the curd
- Ageing
- FINISHED!
How is Camembert made?
With mould- Penicillium camemberti, developing only on the surface rather than throughout the mass.
What’s an example of invasive ripening?
Roquefort cheese. Ripened by mould throughout the cheese mass rather than just on surface.
What kind of fermenters make Ales?
Top fermenters- yeast rises to the surface S. cerevisiae.
What kind of fermenters make Lagers?
Bottom fermentors- yeast settles at the bottom. S. carlsbergensis.
What’s the difference in temperatures in the brewing of ales and lagers?
Ales ferment at hotter temps 20-25’C
Lagers ferment at colder temps 7-15’C
What are the most important aroma compounds in beers? (ales)
Esters. (fruity in ales, less desirable in lagers)
What are fusels alcohols?
Long chain alcohols, contribute to beer and lager favourite. Strong “alcoholic” flavours.
How is citric acid produced for food and drink?
Originally from lemons. Now from Aspergillus niger which secrete large amounts. (need specific conditions)
What’s the problem with non-starch polysaccharides in the poultry industry?
They can’t be absorbed and hang around in the gut, making other absoprtion less efficient too.
How is this solved? The problem with non-starch polysaccharides in the poultry indsutry
By adding beta-glucanase with feed, breaks down the non-starch polysaccharides in the stomach,
What is phytate?
Phytic acid. inorganic phosphate used as phosphate store in plants.
What’s the problem with phytate?
Cannot be degraded by monogastric animals.
How has the problem with phytate been solved?
Traditionally, feed has been supplemented with phosphate, but its was polluting lakes and rivers, causing algal bloom.
Now phytase is used- breaks down phytate.
What’s most food poisoning caused by?
Bacteria (2/3 of the time)
What causes Listeriosis and the symptoms?
- Lysteria monocytogenes. Contamination, raw meat and veg. grows at 4’C.
- Nausea, vomiting, diarrhoea. More serious symptons can cause meningitis.
- Can result in miscarriage in pregnant women.
What are mycotoxins?
Toxic fungal metabolites that accumulate in cereal grains, and other food particularly in storage.
