Dairy Fermentation

Question 1

are all cheeses pressed?

Answer 1

no. some are “unpressed” because the draining process from gravity is enough to knit the curds together

Question 2

pressing

Answer 2

-helps expel whey and knit the curds together.

Question 3

knitting

Answer 3

the fusion of the curds together as the whey drains. Pressing achieves this

Question 4

3 ways salt can be applied

Answer 4

• rubbed on the surface of the finished cheese
• submerged in a concentrated brine
• directly applied to the curd particles before knitting

Question 5

purpose of salting

Answer 5

draws whey to the surface of the curd where it can be released. the greater uptake of salt, the greater expulsion of whey

Question 6

what are the 2 distinct ripening zones?

Answer 6

the body, the surface

Question 7

interior ripening

Answer 7

involves obligate aerobes like mold

cannot occur unless the cheese is broken

Question 8

surface ripening

Answer 8

already exposed to air, so molds will grow naturally or can be added

Question 9

interior ripening example

Answer 9

blue cheese

• not pressed
• needle pokes holes in it to promote o2 entry and co2 exit
• must be turned regularly to prevent moisture buildup and rind rot

Question 10

optimal yogurt temp and pH

Answer 10

42-43C (a compromise between the 2 starter yogurt cultures)

pH of 4.2-4.6 if the pH drops below 4.2 wheying off will occur

Question 11

what are the initial organisms in yogurt

Answer 11

Streptococcus thermophilus

Lactobacillus bulgarius

Question 12

strained yogurt

Answer 12

Greek yogurt
Yogurt that is strained through cloth or paper to remove whey, giving a much thicker consistency and a distinctive tangy taste

Question 13

set yogurt

Answer 13

a solid set where the layers are not disturbed. ie fruit on the top or bottom yogurt

Question 14

dadiah

Answer 14

type of yogurt made from buffalo milk and fermented in bamboo tubes

Question 15

drinking yogurt

Answer 15

stirred yogurt to which additional milk and flavours are mixed in

Question 16

what are the 2 bacteria in yogurt

Answer 16

L. Bulgaricus, S. thermophilicus - symbiotic relationship.

Question 17

what is crucial to the texture development?

Answer 17

heat treatment and acidification because of the way k-casein reacts/is converted

Question 18

the taste in cheese is determined by

Answer 18

acetic acid, diacetyl, acetylaldehyde

Question 19

the taste in yogurt is determined by

Answer 19

lactic acid, acetic acid, diaceytl, acetylaldehyde

Question 20

diacetyl

Answer 20

buttery flavour

produced via the citrate metabolism

Question 21

acetic acid

Answer 21

Bifidiobacteria - vinegary taste

Question 22

acetylaldehyde

Answer 22

most important taste contributer, 40mg/kg

Question 23

what is the importance to a starter culture in dairy fermentations

Answer 23

to monitor the decrease in pH. dairy fermentations need a consistent rate of pH decrease

Question 24

what is the most significant spoilage organisms?

Answer 24

phage

Question 25

how is lactose translocated into the cell?

Answer 25

1. phosphoenolpyruvate phosphotransferase - lactose is phosphorylated and cleaved by phospho-B-galactosidase (lactose -> glucose and galactose-6-phosphate)
   1a. glucose enters glycolytic pathway and GP enters the tagatose pathway to be converted to tagatose-6-phosphate
2. lactose antiport system - lactose is not phosphorylated. glucose enters the glycolytic pathway, galactose accumulates in the cell or is excreted.

Question 26

Leloir pathway

Answer 26

pathway used by Lb. helveticus to metabolize galactose from the lactose antiport system (which wouldn’t have otherwise been useful).

Question 27

detriments to galactose buildup in products

Answer 27

• heterofermentative bacteria will metabolize it causing CO2 and breaks in the cheese.
• galactose can react with amino groups and produce pink or brown colors

Question 28

LAB are auxotrophs for which compound?

Answer 28

amino acids - so they need proteolytic systems to acquire them

Question 29

PrtP

Answer 29

-degrades caseins into oligopeptides, which can be then transported into the cell via Opp
-casein cannot enter cells
-It is attached to the cell via an anchor sequence and
It has broad cleavage specificity (extracellular)

Question 30

what is the effect that proteolysis has on flavour?

Answer 30

bitterness

Question 31

coagulation

Answer 31

• first step in cheese making

- converts milk proteins into a nonpolar form in order to separate them from the water (whey)

Question 32

chemistry of the casein micelle

Answer 32

• hydrophobic inside, polar outside

- Ca helps stabilize it

Question 33

acid coagulation

Answer 33

• pH will decrease naturally and reach the isoelectric point of casein (4.6)
• hydrogen atoms force the casein into chains
• this network traps solid components
• coagulation occurs when micellar Calcium Phosphate is converted into a soluble form and leaves.
• the casein matrix has no MCP and is WEAK.
  2. these cheeses have high water content - cottage cheese, cream cheese

Question 34

heat/acid coagulation

Answer 34

• high heat = denaturation of whey proteins
• denatured whey proteins attach to the micelles and form aggregates that entrap fat globules
  2. these cheeses are high in water content- ricotta, queso blanco

Question 35

rennet

Answer 35

Rennet is a group of proteinases that cleave casein at the surface of casein micelles when added to milk

Question 36

rennet coagulation

Answer 36

• occurs at a high pH 6.6-6.3, before any extensive acidification by starter LAB
• the casein matrix is rich in MCP and very strong

Question 37

what are the 2 important differences between acid and rennet coagulation?

Answer 37

1- Rennet curd is more resilient (less fragile), and better able to expel whey
2- Rennet coagulation occurs quickly (30 -60 minutes)