Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Food Microbiology > Fermented Dairy Products > Flashcards

Fermented Dairy Products Flashcards

1
Q

What microorganisms are used in dairy fermentations? Which is of greatest significance?

A

mold, AAB, LAB, yeast

homofermentative LAB most important

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are LAB so critical in dairy fermentations?

A

must rapidly produce lactic acid -> drop pH

flavor development

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does pH of a dairy ferment affect (terms of quality)?

A 
moisture control
retention of coagulants
loss of minerals
protein hydration
(affect flavor, texture, body of product)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Dairy starter cultures are classified as ____ or ____.

A

mesophilic (25-30C)

thermophilic (37-42C)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

True/False: the most significant threat to the dairy fermentation industry is AAB contamination.

A

False; AAB not issue; phage infection biggest concern

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

___ is the primary carb in milk, composed of ___ and ___.

A

lactose; glucose and galactose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the process for uptake of lactose by LACTOCOCCI: (3 things occur)

A

uptake by transport system (PEP-PT)
Simultaneous phosphorylation (to prevent gradient)
cleaved (phospho-B-galactosidase)
glucose + galactose-6P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are the components of lactose metabolized by LAB?

A

Glucose -> glycolysis

galactose-6P -> tagatose pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

A cheese product has visible cracking, and pink and brown pigments. What is the cause for this and how can it be prevented?

A

Excess excreted galactose from LAB that cannot metabolize it - accumulation in cheese

cracks caused by CO2 from heterofermentative bacteria that eat the galactose
color from rxn with amino groups

Need to include galactose metabolizing strains in culture!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the alternative lactose transport system in non-lactococci LAB? What is the difference?

A

Lactose-galactose antiport system
does not add P; cleaved to give glucose + galactose
galactose excreted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

____ can metabolize galactose through the ____ pathway, and will prevent ______.

A

Lb helveticus
Leloir
accumulation of galactose in cheese

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How does lactic acid in cheese affect aroma?

A

No aroma (not volatile); but contribute to acidity in taste

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What compounds give fermented dairy its aroma? Where do they come from?

A

acetic acid, acetaldehyde, diacetyl

from citric acid in milk -> fermented by LAB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

besides sugars, what nutrient is required for LAB? How can they obtain it from milk?

A

amino acids

free AA not sufficient, use PROTEOLYTIC SYSTEMS to break down milk peptides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

True/False: LAB are considered auxotrophs

A

True (cannot make AA, many other macromolecules)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

the 3 systems needed for proteolysis:

A

extracellular enzymes
transport systems
intracellular enzymes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the significance of PrtP? Where is it found?

A

envelope associated proteinase (EXTRACELLULAR)
in LACTOCOCCI
broad range of cleaving ability, hacks up milk peptides so can uptake

if not present -> cell grow 10x smaller

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the major protein type in milk?

A

Caseins (80%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

True/False: dipeptides and tripeptides are taken up by the same membrane transporter

A

True (Dtp)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

True/False: oligopeptides must be broken down further to enter the cell

A

False; oligopeptides produced by PrtP can be taken up by Opp -> broken down inside cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

the 3 membrane AA transport systems:

A

AAT
Dtp
Opp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What proteolytic enzyme types are inside the cell?

A

aminopeptidases
dipeptidases
tripeptidases
endopeptidases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does the proteolysis affect flavor of the milk?

A

bitterness, flavor development

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

____ is the process in cheese that breaks the milk emulsion/dispersion, and results in separation of _____.

A

coagulation

curds, whey

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

The 3 coagulation methods:

A

acid coagulation
rennet coagulation
acid/heat coagulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How do insoluble proteins remain dispersed in milk? What protein is responsible?

A

contained in micelles, surrounded by KAPPA CASEIN (soluble)

stabilized by Ca phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

How does acid coagulation occur?

A

LAB ferment -> lactic acid -> pH drop to 4.6
micelle polar surface neutralized, Ca Phosphate solubilized -> casein clump into chains
water, fat globules trapped in casein matrix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

acid coagulated cheese form a (strong/weak) gel, which is high in ___.

A

weak

water (70-80%)

29
Q

List some examples of acid coagulated cheese:

A

cottage cheese
quark
cream cheese

30
Q

Are acid coagulated cheese usually aged?

A

No, high moisture -> prone to spoilage

31
Q

What causes the coagulation in acid/heat coagulation? Can it be used alone?

A

heat coagulation

no; micelles are highly heat stable up to 140C (require acid to lower coag temp)

32
Q

Describe the process of acid/heat coagulation

A

acid lowers pH to 6.2-5.4
apply heat 85C
Whey proteins unfold -> clump with caseins -> trap fat
Drain, press curds

33
Q

Ricotta and queso blanco are examples of ____ coagulation. They are relatively high in ____.

A

acid/heat

moisture

34
Q

What are the advantages of rennet vs acid coagulation?

A
  1. firmer curd, expel more whey

2. faster (30-60min)

35
Q

How does rennet coagulation occur?

A

rennet (enzymes) target k-casein

k casein cleaved -> micelle insoluble -> caseins form matrix trapping fat (curds)

36
Q

What is rennet and where does it come from?

A

mix of proteinases that cleave caseins

animal, plant, microbial sources (most common)

37
Q

rennet cheese are low in ___, and can be aged.

A

moisture

38
Q

What is important to consider in early stages of rennet cheese making?

A
  1. correct amount of whey expelled
  2. rate of acidification
  3. rate of salt addition
39
Q

True/False: rennet cheese do not require acidification

A

True; can occur at 6.6-6.3

40
Q

What is “cutting” in cheese making? What is the purpose?

A

break up coagulum

more surface area -> more whey expulsion

41
Q

What step occurs after the whey expulsion in the cheese? What does this step accomplish?

A

cooking

promote curd contraction
high temp -> LAB make more acid -> more curd contraction
contraction squeeze out more whey

42
Q

Cooking the whey and curd for longer at a (higher/lower) temp will produce a curd that has less ____.

A

higher

moisture

43
Q

How are the curds removed from whey and why is this necessary?

A

Dripping: scoop out, put in draining mold
Draining: take out curds from strainer in the vessel, leave whey behind
Industrial: pump out onto draining table, let whey drip

curds need to fuse to form the cheese

44
Q

____ describes the fusion of the cheese curd. ____ is a similar process but involves pressure and produces ____ cheeses

A

Knitting
Pressing
compact (salt brine cheeses, swiss cheeses)

45
Q

Why is salting important in cheesemaking?

A

osmotic force: draws out more whey

46
Q

How is salting done?

A
  1. rub dry salt on surface of cheese
  2. submerge in brine
  3. add to curd before knitting
47
Q

Finishing transforms ____ into finished cheese

A

green cheese

48
Q

True/False: only finished cheese should be salted

A

false; can add to curd

49
Q

What are some considerations in the finishing process?

A

depends on cheese;

temperature, humidity, surroundings, microflora, manipulations, etc

50
Q

The 2 ripening zones in cheese:

Why are they different?

A 
interior and exterior
different environments (aerobic vs anaerobic)
51
Q

What are examples of interior ripening and how is this done?

A

blue cheeses
poke with needles to make air shafts so mold can grow
(P. roqueforti added to milk)

52
Q

Are blue cheeses pressed? Why or why not?

A

no; need to be somewhat permeable to air to allow mold to grow

53
Q

Blue cheeses should be turned regularly to avoid ____

A

rind rot, moisture accumulation

54
Q

The 2 groups of surface ripened cheese:

What category is Brie and Camembert?

A 
Low pH (<5)
High pH (>5)

brie/camembert are low pH

55
Q

What is the microbe in camembert ripening and what does it do?

A

P. camemberti (mold)

break down lactic acid (pH rises)

56
Q

The temperature range of yogurt fermentation is ____, because the cultures used are _____.

A

42-43C

thermophilic

57
Q

What is the optimal endpoint for yogurt pH? What happens if the ferment continues?

A

4.2-4.6

if continue, pH keep dropping -> wheying off

58
Q

yogurt starter cultures usually have ____ and ___. In what proportion?

A

Strep. thermophilus, Lactobacillus bulgarius

equal numbers

59
Q

What are the optimal temps for S thermophilus and L bulgarius?

A

St: 37C
Lb: 45C

60
Q

Describe the symbiotic relationship of S. thermophilus and L. bulgarius in yogurt:

A

Lb has proteases (PrtP), breaks down milk proteins
St not as good at proteolysis, uses peptides made by Lb; St also use intermediate products from Lb

St make formic acid and CO2 -> acts as growth factor for Lb

61
Q

Describe the population dynamics through the yogurt process

A

beginning: St grows fastest, biggest population
Middle: lower pH and growth factors stimulate Lb to grow (Lb more acid tolerant); Lb breakdown proteins to feed St
End: 1:1 population, about 2x10^7 each

62
Q

List some yogurt types

A

stirred yogurt (mixed with sugar, flavorings, fruit)
Greek yogurt (drained)
Set yogurt (set in container, not disturbed)
drinking yogurt: (added milk and flavors)
yogurt cheese (drained)
frozen yogurt

63
Q

What gives yogurt its gel-like texture?

A

interaction between acid-destabilized k-casein and heat destabilized whey proteins (similar to acid/heat coagulated cheese)

64
Q

At pH ___, Ca phosphate is _____, causing the micelle to lose its structure.

A

5.0

soluble; released from casein micelle

65
Q

Flavor compounds in yogurt:

Which is most important?

A

Lactic acid
Diacetyl
Acetaldehyde (most important) - 40mg/kg
Acetic acid

66
Q

How can using Bifidobacteria affect the taste of yogurt?

A

makes more acetic acid -> more vinegary taste

67
Q

Inclusion of citrate positive bacteria will influence yogurt flavor in what way?

A

create diacetyl -> buttery taste

68
Q

True/False: fresh fruit will contribute to yogurt positively

A

False; usually use dry/frozen/processed fruit to avoid spoilage from yeast/mold

69
Q

Activia yogurt is marketed as containing a strain called _____.

A

Bifidobacterium animalis

Food Microbiology (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions