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FDSC442 > 7- fermented dairy > Flashcards

7- fermented dairy Flashcards

1
Q

At the moment the most significant threat to the fermented milk products industry is ____

A

phage

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2
Q

why is homofermentative LAB important in the dairy industry?

A

because of the rapid drop in pH

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3
Q

T or F : The main function of LAB is to ferment lactose into lactic acid, it is not their only function, they also are involved in the development of flavor

A

true

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4
Q

____is the main metabolite at the end of a diary fermentation

A

Lactic acid

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5
Q

The main volatile and flavor components of fermented milks are____, ___ and _____

A

acetic acid, acetaldehyde, and diacetyl

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6
Q

What is a auxiotrophs?

A

organism (especially a bacterium or fungus) that requires a particular additional nutrient which the normal strain does not

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7
Q

How does LAB hydrolyse proteins?

A

with the PrtP proteinse attached to its cell wall.

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8
Q

____ is essential for uptake of peptides from the breakdown of casein via PrtP

A

Opp

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9
Q

What are the three way of making cheese coagulate

A

Rennet-coagulated Acid-coagulated Acid/heat-coagulated

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10
Q

How does acid coagulation works

A

As pH decreases, the isoelectric point of casein (pH 4.6) is reached, hydrogen atoms accumulate and neutralize the polar surfaces of casein micelles, forcing them into chains of micelles

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11
Q

What is the coagulum?

A

The soft fragile gel that is formed over the course of hours by the coagulation of the milk

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12
Q

How does the acid / heat coagulation works ?

A

However, if milk is moderately acidified (pH 6.2-5.4) it becomes susceptible to heat-induced coagulation at relatively low temperatures (85C)

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13
Q

How is make queso-blanco (type of coagulation)?

A

It is a pressed version of ricotta made from a acid / heat coagulation

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14
Q

What is the type of coagulation that expels more whey than the others

A

the rennet coagultion

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15
Q

How does the rennet coagulation works?

A

Rennet preferentially cleaves the K-casein at the surface of the micelles and initiates coagulation

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16
Q

What are two advantages of using rennet for the coagulation?

A

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

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17
Q

Why isn’t LAB lost with the whey when you drain your curds

A

The LAB are trapped in the matrix of the curd

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18
Q

What are the goals in the cooking step in the cheese making?

A
  • It promotes the curd contraction
  • Cooking also influences the rate of lactic acid production by LAB, which also causes the curds to contract and expel more whey as the pH decreases
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19
Q

What are the two methods of separating the curds from the whey?

A

Dripping: where curd-whey mixture is scooped out and placed in a draining vessel (ceramic sieve, wicker basket, or actual plastic draining mold)
Draining: were there is a fitted valve or a strainer in the vessel used for coagulation and the whey is simply drained off

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20
Q

What is knitting?

A

it is the term used to describe the fusion of curds together as the whey drains to produce once continuous mass of fused cheese curd

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21
Q

What is pressing?

A

Pressing is closely related to knitting and involves the application of external pressure to the curd during knitting (or in some cases after knitting)

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22
Q

What is the goal of salting the cheese?

A

Thus salting is yet another step to expel moisture from the cheese, the greater the uptake of salt the greater the release of whey

23
Q

Surface ripened cheeses include two groups, what are they

A

Low pH at surface (pH<5) High pH at surface (pH>5)

24
Q

What are the microorgasnisms used in dairy fermentations

A
  1. molds 2. yeasts 3. LAB 4. AAB
25
Q

what is the function of the LAB in the fermented dairy products

A
  1. ferment lactose into lactic acid 2. development of flavor
26
Q
A
27
Q

what is the name of the bacteria that is able to transport galactose and utillize the leloir pathway to metabolize it

A

the Lb. Helveticus

28
Q

why can galactose be a problem?

A

it can cause several problems for the cheese if there is no strains able to metabolize it because it can :

  1. There can be production of CO2 and cracks in the cheese (by the heterofermentative)
  2. residual galactose can react with a.a. and form colored compounds
29
Q

explain the proteolytic system in lab

A
30
Q

•PrtP degrades ___ effectively into oligopeptides

A

caseins

31
Q

PrtP is found in ____

A

lactococci

32
Q

what determines the flavor development in dairy products

A

•The proteolytic enzymes present in the milk matrix determine which peptides and amino acids accumulate and how flavor develops

33
Q

what is coagulation?

A

•is the first pivotal step in cheese making, where all of the proteins are converted into a non-polar form and when this occurs they separate from the water phase though a process that entraps fat and minerals (curd contraction and whey expulsion)

34
Q

what is the disadvantage of the rennet-coagulated cheeses?

A

the rippening procdess is unforgiving.

35
Q

what are the objectives that needs to be achieved when making cheese from rennet?

A
  1. the correct amound of whey needs to be expelled
  2. The rate of acification must be controlled
  3. The salt must be incorporated at the correct rate
36
Q

what is the goal of the cooking step in cheese making?

A

•Cooking to a higher temperature, for a longer duration and with more stirring promotes curd contraction

37
Q

why is there orange molds that can appear on cheese when you use penicilum camenmberti

A

•P. camemberti rapidly catabolizes lactic acid and results in deacidification of the cheese surface (making the cheese prone to contamination by some bacteria that produce orange or yellow pigments)

38
Q
A
39
Q

•The starting temperature of milk used in the the average yogurt fermentation is ______ when the inoculation of LAB occurs

A

42-43∘C

40
Q

what is the optimal pH for the yogurt production

A

4.2-.4.6

41
Q

what are the two LAB in yogourt production

A

L. bulgaris and S. Termophilus

42
Q

•____ is known to have several cell-bound proteases (PrtP) that cleave proteins into amino acids extracellularly

A

L. bulgaricus

43
Q

__ and ___ produced by S.thermophilus are growth factor of the L.bulgaris

A

Formic acid and CO2

44
Q

What does the L.bulgaris that helps the growth of S.termophilus

A

it cleaves casein proteins into smaller peptides that the S.thermophilus can use

45
Q

what is dadiah?

A

Dadiah: Made from water buffalo milk and fermented in bamboo tubes

46
Q

what is strained yogourt?

A

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

47
Q

What is set yogourt?

A

a solid set where the yogurt forms and is not disturbed
Fruit-on-the-bottom yogurt
Fruit-on-the-top yogurt

48
Q

What is stirred yogourt

A

Yogurt is made in a large container and then spooned into a secondary serving container

49
Q

*What are the key in texture development of yogourt?

A

Heat treatment and acidification

50
Q

how can we explain the textural changes in yogourt?

A

During acidification, at pH 5.0, the calcium phosphate is completely released from the casein micelle, and the integrity of the micelle is reduced, the denatured whey proteins also interact with k-casein increasing hydrophobicity, consequently, when the micelles become unstable aggregation starts which leads to gelation

51
Q

Taste in yogourt is determined by :

A
  • Lactic acid
  • Acetaldehyde
  • Acetic Acid
  • Diacetyl
52
Q

in yogourt ___ is probably the most important contributor to taste and LAB have a variety of pathways to produce acetaldehyde

A

Acetaldehyde

53
Q

____ produce a little more acetic acid than other LAB and will produce a more ”vinegary” taste

A

•Bifidobacteria

54
Q
A

FDSC442 (19 decks)

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