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FDSC 442 > Fermented Dairy Products > Flashcards

Fermented Dairy Products Flashcards

1
Q

what bacteria are involved in dairy fermentations?

A

molds, yeast, AAB, and LAB

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2
Q

what is the most important bacterium in the fermented dairy industry?

A

homo fermentative LAB

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3
Q

what is LAB’s role in dairy fermentation?

A

the main role of LAB is to ferment lactose into lactic acid, but they also contribute to development of flavor

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4
Q

what kind of fermentation does dairy fermentation perform under?

A

inoculated fermentation

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5
Q

what kind of LAB cultures are used?

A

mesophilic (optimal growth between 25-30C) and thermophilic (optimal growth between 37-42C)

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6
Q

what two things are critical to successful dairy fermentation?

A

rate of acidification, and extent of pH decrease

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7
Q

what is the most significant threat to the fermented milk products industry?

A

phage

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8
Q

What are the steps of lactose metabolism?

A

LAB utilize lactose, the primary carbohydrate in milk. LAB convert lactose into glucose either by using phospho-B-galactosidase and B-glactosidase. Glucose then goes through the glycolytic cycle, turning into pyruvic acid and then lactic acid as the final product.

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9
Q

What are the two pathways involved in LAB metabolism, besides the glycolytic pathway?

A
  1. Tagatose pathway - if phospho B-galactosidase is used

2. Leioir pathway - if B-galactosidase is used

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10
Q

what does B-galactosidase do?

A

cleaves lactose into glucose and galactose when lactose isn’t phosphorylated.

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11
Q

what bacteria is able to transport galactose?

A

Lb. helveticus, transports galactose and utilize the Leloir pathway to metabolize it

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12
Q

what happens if galactose is metabolized too fast?

A

heterofermentative bacteria will produce too much CO2, forming cracks in the cheese. Or, residual galactose can react with amino groups causing pink to brown pigments to form

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13
Q

what Aromatic compounds are involved in dairy fermentation

A

acetic acid, acetaldehyde, and diacetyl

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14
Q

what can citric acid, contained in milk, be metabolized to?

A

diacetyl, acetic acid, and carbon dioxide

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15
Q

What is the role of Proteolytic Systems in LAB?

A

to break down essential peptides needed for LAB growth and fermentation. The breakdown of peptides/hydrolyzing milk proteins gives LAB its essential amino acids.

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16
Q

what are the three categories of proteolytic systems in LAB?

A
  1. enzymes outside the cytoplasmic membrane
  2. transport systems
  3. intracellular enzymes
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17
Q

what is PrtP?

A

envelope associated proteinase which breaks down caseins effectively into oligopeptides

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18
Q

what are the three modes of transport of amino acids across the cytoplasmic membrane?

A
  1. amino acid transport systems (AAT)
  2. Di- and tri- peptide transport systems (Dtp)
  3. oligopeptide transport systems (Opp)
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19
Q

what does Opp do?

A

take up proteins from the breakdown of casein via PrtP

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20
Q

what are the peptidases involved?

A
  1. aminopeptidases
  2. Dipeptidases
  3. Tripeptidases
  4. Endopeptidases
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21
Q

What is coagulation?

A

the first critical step in cheese making, where all the proteins are conveted into a non-polar form which causes them to separate from the water phase through a process known as curd contraction and whey expulsion

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22
Q

What are casein micelles?

A

soluble coagulations of the casein protein

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23
Q

what is the role of K-micelle?

A

keeps the micelle soluble by maintaining its polarity. located on the surface of the casein micelle.

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24
Q

how does the micelle maintain its structure?

A

the core of the molecule is hydrophobic (nonpolar), and calcium phosphate stabilizes the micelle

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25
Q

how does acid coagulation occur in fermenting milk?

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. the network of casein micelles entraps all of solid components

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26
Q

what are the characteristics of acid-coagulated cheeses?

A

casein matrix is very fragile and can only expel so much whey so acid-coagulated cheese are generally quite high in water content (70-80% moisture)

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27
Q

what is acid/heat coagulation?

A

the process of fermenting milk undergoing heat-induced coagulation at relatively low temperatures, if milk is moderately acidified. this causes the denatured whey proteins to attach onto micelle surfaces and the micelles aggregate into clusters

28
Q

what cheese is an example of acid/heat coagulation?

A

ricotta

29
Q

What is rennet coagulation?

A

rennet is a group of proteinases that cleave casein at the surface of casein micelles when added to milk. specifically cleaves K-casein at the surface initiating coagulation

30
Q

what is the effect of cleaved k-casein?

A

casein micelles lose polarity which causes coagulation

31
Q

two important differences between rennet coagulation and acid coagulation?

A
  1. rennet curd is more resilient and better able to expel whey
  2. rennet coagulation occurs quickly (30-60 min)
32
Q

what is unique about the rennet-coagulated ripening process?

A

it is unforgiving (and could take up to years to complete)

33
Q

what is the point of cutting?

A

breaks up the coagulum to increase surface area and speed up the ripening process through rapid release of whey

34
Q

what is the point of cooking?

A

applies heat to fermented cheese to also increase expulsion of whey and promote further curd contraction

35
Q

What is the function of Dripping and Draining?

A

dripping drains the whey out of the curd-whey mixtures so that the curd particles can fuse together and form a larger entity. Draining also does this by putting the curd-whey mixture into a strainer or vessel.

36
Q

What is the function of knitting?

A

for further expulsion of whey to produce one continuous mass of fused cheese curd. whey is expeled in a temperature dependent manner.

37
Q

what is the function of pressing?

A

pressing is similar to knitting and involves the application of external pressure to the curd during knitting

38
Q

what does salting do to the cheese?

A

creates an osmotic driving force that draws whey to the surface of the curd where it is released. another step to expel moisture from the cheese. the greater the uptake of salt, the greater the release of whey

39
Q

what are the three ways salt can be applied to cheese?

A
  1. dry salt rubbed onto the surface of the finished cheese
  2. cheese submerged in a concentrated brine solution
  3. applied directly to the curd particles before knitting
40
Q

what does the finishing process of cheese fermentation require?

A

a specific combination of environmental conditions (temperature, humidity, physical surroundings, presence of microflora, and sometimes manipulations like rubbing, salting, scraping, turning, or washing)

41
Q

what are the two ripening zones of cheese?

A
  1. body (interior of cheese)
  2. surface
    these two zones represent significantly different microbiological conditions
42
Q

what does interior ripening involve?

A

obligate anaerobes such as LAB which cannot grow in the cheese interior

43
Q

what does surface ripening involve?

A

takes place on the cheese surface

44
Q

what cheese uses interior ripening?

A

blue cheese. requires mold growth. cheese is pierced with needles at the start of ripening where carbon dioxide can vent out and oxygen can diffuse in

45
Q

what cheeses undergo surface ripening?

A

Brie and Camembert

46
Q

what conditions promote optimal surface ripening on cheeses?

A

low pH and high humidity

47
Q

what is the general process of yogurt production?

A
  1. milk is heated to 42-43C

2. inoculated with LAB

48
Q

what is the optimal pH for yogurt fermentation?

A

4.2-4.6

49
Q

what are the starter cultures in yogurt fermentation?

A
  1. Streptococcus Thermophilus

2. lactobacillus Bulgarius

50
Q

what temperature is yogurt incubated at?

A

42C

51
Q

What is the starter culture you used for yogurt fermentation in the lab?

A
  1. S. thermophilus,
  2. L. bulgarius,
  3. Bfidiobacterium infantis,
  4. B. longum, and
  5. B. bifidum
52
Q

what is the key to a successful yogurt starter?

A

producing an obligate symbiotic relationship where the acid and flavor produced by the blend of the mixed culture is considerably higher than by either of the two organisms separately

53
Q

What does S. thermophilus produce?

A

purine, pyrimidine, CO2, formic acid, oxaloacetic acid, and fumaric acid

54
Q

What bacterium grows the fastest in yogurt starter culture?

A

S. thermophilus

55
Q

which bacterium of yogurt starter culture grows best at low pH

A

L. bulgaricus

56
Q

what is the relationship between S. thermophilus and L. bulgaricus in yogurt starter culture?

A

the growth of L. bulgaricus produces peptides and amino acids which then stimulates the growth of S. thermophilus

57
Q

what is the ratio of all the bacteria in yogurt starter culture at the end of yogurt fermentation?

A

1:1

cell count for each bacterium is 2x10^7 cells/mL

58
Q

What are the types of yogurt?

A
  1. Stirred yogurt
  2. Set yogurt
  3. Drinking yogurt
  4. Yogurt cheese
  5. Frozen yogurt
  6. Strained yogurt
  7. Dadiah
59
Q

what does the “gel” like texture in yogurt come from?

A

the interaction between acid destabilized k-casein and heat denatured whey proteins

60
Q

what is the key to texture development?

A

heat treatment and acidification

61
Q

how do micelles aggregate in yogurt development?

A

denatured whey proteins that interact with k-casein increase hydrophobicity which causes micelles to become unstable and aggregate leading to gelation

62
Q

what stabilizers are used in yogurt fermentation?

A

pectin or gelatin

63
Q

What compounds contribute to taste in yogurt?

A
  1. Lactic Acid
  2. Acetaldehyde
  3. acetic acid
  4. diacetyl
64
Q

what is the most important contributor to taste in yogurt

A

acetaldehyde

65
Q

what is the most popular type of yogurt in western societies?

A

Stirred fruit yogurt

66
Q

what are the advantages of using processed fruits in yogurt?

A
  1. entirely free from yeasts and molds
  2. level of color
  3. degree of sweetness can be adjusted by adding sucrose
67
Q

what was the significance of activia?

A

developed a strain, bfidobacterium animalis, that was able to survive lactic acid in yogurt

FDSC 442 (13 decks)

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