L11- Microbes and food

Question 1

What is Rennet?

Answer 1

A complex of enzymes made in stomachs of ruminants which is used in the production of most cheeses. It’s main component is chymosin.

Question 2

What’s chymosin?

Answer 2

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).

Question 3

What’s paracasein?

Answer 3

The treated casein. Paracasein removes charged peptide side chains from K-casein which causes coaggulation in the presence of calcium and –> curds

Question 4

Why does the charge have to be removed from the casein?

Answer 4

The surface charge around casein micelles separates them.

Question 5

Which conditions does Rennet work best in?

Answer 5

Acidic conditions. So lactobacilli (bacteria) added first which acidifies it.

Question 6

What is 90% of hard cheese made using?

Answer 6

Recombinant calf chymosin from Aspergillus niger. (only calves naturally produce chymosin)

Question 7

What’s Rennet used to separate out in cheese?

Answer 7

Curds and whey

Question 8

What are the main stages of making cheese?

Answer 8

1. precuring at warm temp. (lactobacilli acidifies)
2. Coagulation by Rennet
3. Separation of the whey
4. Compression of the curd
5. Ageing
6. FINISHED!

Question 9

How is Camembert made?

Answer 9

With mould- Penicillium camemberti, developing only on the surface rather than throughout the mass.

Question 10

What’s an example of invasive ripening?

Answer 10

Roquefort cheese. Ripened by mould throughout the cheese mass rather than just on surface.

Question 11

What kind of fermenters make Ales?

Answer 11

Top fermenters- yeast rises to the surface S. cerevisiae.

Question 12

What kind of fermenters make Lagers?

Answer 12

Bottom fermentors- yeast settles at the bottom. S. carlsbergensis.

Question 13

What’s the difference in temperatures in the brewing of ales and lagers?

Answer 13

Ales ferment at hotter temps 20-25’C

Lagers ferment at colder temps 7-15’C

Question 14

What are the most important aroma compounds in beers? (ales)

Answer 14

Esters. (fruity in ales, less desirable in lagers)

Question 15

What are fusels alcohols?

Answer 15

Long chain alcohols, contribute to beer and lager favourite. Strong “alcoholic” flavours.

Question 16

How is citric acid produced for food and drink?

Answer 16

Originally from lemons. Now from Aspergillus niger which secrete large amounts. (need specific conditions)

Question 17

What’s the problem with non-starch polysaccharides in the poultry industry?

Answer 17

They can’t be absorbed and hang around in the gut, making other absoprtion less efficient too.

Question 18

How is this solved? The problem with non-starch polysaccharides in the poultry indsutry

Answer 18

By adding beta-glucanase with feed, breaks down the non-starch polysaccharides in the stomach,

Question 19

What is phytate?

Answer 19

Phytic acid. inorganic phosphate used as phosphate store in plants.

Question 20

What’s the problem with phytate?

Answer 20

Cannot be degraded by monogastric animals.

Question 21

How has the problem with phytate been solved?

Answer 21

Traditionally, feed has been supplemented with phosphate, but its was polluting lakes and rivers, causing algal bloom.
Now phytase is used- breaks down phytate.

Question 22

What’s most food poisoning caused by?

Answer 22

Bacteria (2/3 of the time)

Question 23

What causes Listeriosis and the symptoms?

Answer 23

• 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.

Question 24

What are mycotoxins?

Answer 24

Toxic fungal metabolites that accumulate in cereal grains, and other food particularly in storage.

Question 25

Type of mycotoxin- Aflatoxins?

Answer 25

Highly toxic and carcinogenic. Affects men and livestock.

Question 26

What;s Ergot poisoning?

Answer 26

Illness sporadic through history. Caused by Claviceps purpurea. “ St. Antony’s fire”. Joint pain, hallucinations, seizures.