Dairy

Question 1

Why ferment milk?

Answer 1

1. extend shelf life
2. Increase flavors and texture

Question 2

What is milk made of an approx which percentages?

Answer 2

85% water
4% fat
3.4% protein
4.6% lactose
and then other smaller thigns

Question 3

What are the main proteins in milk?

Answer 3

Casein and whey

Question 4

Which are the main types of whey?

Answer 4

B-lactoglobulin (50%), a-lactalbumin (20%), blood serum albumin, lactoferrin etc the rest

Question 5

Order the following from largest to smallest, casein, fat globule and whey.

Answer 5

Fat globule > Casein micelle > Whey proteins

Question 6

What are the casein micelles made of (which subunits)? how are they hold together?

Answer 6

a-s1, a-s2 and B and are held together by calcium phosphate bridges.

Question 7

How are casein micelles stabilized against aggregation?

Answer 7

By k-casein

Question 8

How does reduction of pH lead to casein micelle aggregation?

Answer 8

pH reduction disrupts ionic interactions betweeen the casein phosphate groups and calcium ions leading to casein protein to denature. As the pH approaches pI caseins start to coagulate.

Question 9

How can whey proteins be incorporated in the gel strcuture of casein?

Answer 9

By pasteurization, B-lactoglobulin will form covalent bonds with k-casein and will be incorporated in the gel network.

Question 10

How can fat globules be incorporated in the gel structure of casein?

Answer 10

By homogenization of the fat globules which behave as filler gels and will increase gel strength. If the fat globules are too large they can disrupt the casein micelle network and decrease the gel strength.

Question 11

What are the two most relevant starter cultures for yoghurt?

Answer 11

1. Streptococcus
2. Lactobacillus

Question 12

What are the reasons of using S. thermophilus?

Answer 12

Can rapidly convert lactose into lactic acid

Question 13

What are the reasons of using L. bulgaricus

Answer 13

Bulgaricus is more proteolytic which allows hydrolyzation of casein, especially B-casein.

Question 14

What do exopolysaccharides do the the structure of the yoghurt?

Answer 14

Gives it a rocky structure

Question 15

What is the optiaml pH of S. thermophilus and LB. bulgaricus?

Answer 15

6.0-6.5 and 3.5-3.8

Question 16

What is meant by protocooperation?

Answer 16

Is a symbiotic interaction based on the exchange of several metabolites which provide mutual growth-stimulating effects.

Question 17

How does the protocooperation of S. thermophilus and Lb. bulgaricus work?

Answer 17

S. thermophilus will produce Formic + Folic acid, increase CO2 and reduce O2. These factor will stimulate Lb. bulgaricus growth as well as lactic acid which reduces pH to optimal. Lb. bulgaricus growth will produce amino acid peptides due to its proteolytic activity and stimulate S. thermophilus growth. In the end lactic acid will reduce pH so much that it will inhibit the growth of both bacteria.

Question 18

Which one can be a harmful enantiomer, L or D-Lactic acid?

Answer 18

D-lactic acid

Question 19

How can one monitor growth of LAB? There are four possible options.

Answer 19

1. Decrease of lactose
2. Increase of galactose
3. Increase of lactic acid
4. pH decrease

Question 20

How can one measure lactic acid content?

Answer 20

By titration and comparison to normal milk which contain almost no lactic acid

Question 21

What are the two type of yoghurts and how are they made?

Answer 21

1. Set yoghurt -> fermented inside the pot they are sold. Firm and thick texture.
2. Stirred yoghurt -> when fermentation is carried out in bulk and not individual containers and also stirred. Smooth viscous liquid.

Question 22

What is the difference in gel structure between set and stirred yoghurt?

Answer 22

Set is a large protein aggregate while stirred yoghurt is many individual gel particles.