Dairy Flashcards
Why ferment milk?
- extend shelf life
- Increase flavors and texture
What is milk made of an approx which percentages?
85% water
4% fat
3.4% protein
4.6% lactose
and then other smaller thigns
What are the main proteins in milk?
Casein and whey
Which are the main types of whey?
B-lactoglobulin (50%), a-lactalbumin (20%), blood serum albumin, lactoferrin etc the rest
Order the following from largest to smallest, casein, fat globule and whey.
Fat globule > Casein micelle > Whey proteins
What are the casein micelles made of (which subunits)? how are they hold together?
a-s1, a-s2 and B and are held together by calcium phosphate bridges.
How are casein micelles stabilized against aggregation?
By k-casein
How does reduction of pH lead to casein micelle aggregation?
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.
How can whey proteins be incorporated in the gel strcuture of casein?
By pasteurization, B-lactoglobulin will form covalent bonds with k-casein and will be incorporated in the gel network.
How can fat globules be incorporated in the gel structure of casein?
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.
What are the two most relevant starter cultures for yoghurt?
- Streptococcus
- Lactobacillus
What are the reasons of using S. thermophilus?
Can rapidly convert lactose into lactic acid
What are the reasons of using L. bulgaricus
Bulgaricus is more proteolytic which allows hydrolyzation of casein, especially B-casein.
What do exopolysaccharides do the the structure of the yoghurt?
Gives it a rocky structure
What is the optiaml pH of S. thermophilus and LB. bulgaricus?
6.0-6.5 and 3.5-3.8
What is meant by protocooperation?
Is a symbiotic interaction based on the exchange of several metabolites which provide mutual growth-stimulating effects.
How does the protocooperation of S. thermophilus and Lb. bulgaricus work?
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.
Which one can be a harmful enantiomer, L or D-Lactic acid?
D-lactic acid
How can one monitor growth of LAB? There are four possible options.
- Decrease of lactose
- Increase of galactose
- Increase of lactic acid
- pH decrease
How can one measure lactic acid content?
By titration and comparison to normal milk which contain almost no lactic acid
What are the two type of yoghurts and how are they made?
- Set yoghurt -> fermented inside the pot they are sold. Firm and thick texture.
- Stirred yoghurt -> when fermentation is carried out in bulk and not individual containers and also stirred. Smooth viscous liquid.
What is the difference in gel structure between set and stirred yoghurt?
Set is a large protein aggregate while stirred yoghurt is many individual gel particles.
