Milk and Dairy Flashcards
1
Q
What countries are the top 3 milk producers?
A
- USA
- India
- China
2
Q
The top 2 producers of milk among Canadian provinces are:
A
Ontario, Quebec
3
Q
Milk is defined as:
A
fluid from mammary glands of mammals, produced for the purpose of feeding their young
4
Q
The most produced type of milk is ___, followed by ___, ___, and ____.
A
Cow; buffalo, goat, sheep
5
Q
What hormone plays a major role in milk production and release?
What hormone supplement may be given to lactating cows to increase production?
A
oxytocin
bovine somatotropin
6
Q
List the main components of (whole) bovine milk in increasing proportion:
A
vit&minerals < protein (whey < casein) < fat < sugar
7
Q
the 3 major dairy companies in Quebec:
A
Saputo
Parmalait
Agropur
8
Q
Describe the general process of milk production in the mammal: (6)
A
- oxytocin bind to secretory cells of ALVEOLUS
- fluid enters lumen of alveolus
- fat globules, proteins, lactose synthesized and secreted by SC -> added to milk
- albumin and immunoglobulins transported from blood and added
- electrolytes brought in from pumps or channels
- milk flows into CISTERN -> ready to exit through teat
9
Q
What is the major sugar in milk? Describe its synthesis process.
A
Lactose
- Glucose taken into secretory cell
- some will freely diffuse into golgi
- Some convert into galactose in lumen (glu -> Glu-P -> UDP-Glu -> UDP-Galactose)
- UDP-galactose moved into golgi (ACTIVE TRANSPORT)
- Combined by LACTOSE SYNTHETASE
10
Q
In the production of milk in the mammary gland, what do the secretory cells synthesize and contribute?
What is not synthesized by those cells?
A
Proteins (most)
Fat globules
Sugar (lactose)
Not made by SC:
albumin
immunoglobins
electrolytes
11
Q
The secretion of lactose into milk will be accompanied by ____, due to _____.
A
water
osmotic draw
12
Q
The proteins synthesized by alveolar cells are made in the ____ of the cells.
A
ribosomes
13
Q
the fat globules of milk are produced in the ___ of the ____ cells.
A
ER
secretory alveolar
14
Q
What is the top dairy breed in Canada?
What are some other types?
A
Holstein (93%)
Jersey, Ayrshire, Brown swiss
15
Q
What is the average lactation length and amount for cows?
A
305 days
7000 - 20 000 kg
16
Q
What is bST, and what is it used for? How is it produced?
A
bovine somatotropin, permitted in some countries to stimulate milk production
produced by transferring gene for hormone production from cow to e. coli -> ferment -> harvest and purify protein hormone
17
Q
How is the secretion by SC of fat globules into milk different from other components such as lactose?
A
Most components exocytosed: vesicles bud off from golgi, travel to surface and fuse with cell membrane, contents released
Fat globules: brought to cell surface, bud outside, encased in membrane (becomes membrane bound lipid globule)
18
Q
Are milk fat globules high in cholesterol?
A
No, smallest constituent (2%)
19
Q
True/False: milk fat contains a high level of MAGs.
A
False: least constituent (0.02-0.04%)
20
Q
The 4 main lipids types in milk fat are: (list in decreasing order)
A
TAG, DAG, PL, keto-acid glycerides
21
Q
The biggest constituent of a milk fat globule is ____, followed by ______.
A
protein (41%)
phospho and glyco lipids (30%)
22
Q
What fatty acid is the highest in milk?
A
palmitic (C16), about 24%
23
Q
What is greater in milk, the amount of short chain FAs or the amount of PUFAs ?
A
short chain FAs
24
Q
The 3 highest SFAs in milk are:
A
C16, C14, C18
25
What are the proportions of SFAs, MUFAs, and PUFAs in milk fat?
SFA: 55% (C4 - C18 most common)
MUFA: 19.7%
PUFA: 3.5%
26
The second most common fatty acid in milk is:
oleic acid (C18:1)
27
```
What are the shorthand chem notations for:
lauric acid
myristic acid
palmitic acid
stearic acid
```
C12
C14
C16
C18
28
The 3 types of PUFAs in milk:
omega 6, omega 3, CLA (conj. linoleic acid)
29
The phospholipids in milk fat globules are associated with:
| Why would this be problematic, and what is done to rectify it?
LIPOPROTEIN LIPASE (enzyme)
during homogenization, membrane is disrupted and enzyme comes into contact with FA -> will hydrolyze and oxidize, make off-flavors (rancidity)
so: need pasteurization (heat treatment) to denature enzyme
30
C18:1 and C16:1 are known as:
oleic acid; palmitoleic acid
31
In WHOLE milk that is not processed, what will eventually happen due to the fat globules? Is this desirable or not, and what process is used to prevent it?
coalesce into bigger globules -> rise to surface
PHASE SEPARATION
good for when want to take out milk fat (make butter, cream)
bad for drinking milk (want smooth even product)
can HOMOGENIZE: break up fat molecules mechanically
32
Which should occur first: homogenization, or pasteurization?
pasteurization: deactivate LPL (otherwise milk will become rancid within minutes after homogenization)
33
milk has a (small/wide) range of FA types. How does this affect its physical properties?
wide
many different melting points -> very gradual melting along range of temperatures
(spreadability)
34
which would go rancid faster: raw or homogenized milk (both are unpasteurized)?
homogenized (membranes are disrupted)
| raw milk globules are still intact, less lipid oxidation occurs
35
describe the two methods of milk/fat separation.
gravitational: allow to separate naturally
put in shallow pans -> skim off top
or: put in narrow tank -> spout at bottom collect liquid
centrifugal: spin at high speed to quickly separate (much more efficient, better recovery)
36
Milk protein may be classified as ____ or ____. How are they distinguished?
Casein; Whey
caseins have similar isoelectric point of pH 4.5 - will precipitate out; also are high in P and thus have Ca binding ability
several very hydrophobic AA regions -> easily aggregate
Whey have various isoelectric points (leftoever in liquid after removal of casein); does not have P, cannot bind Ca
37
What causes caseins to precipitate out?
at isoelectric point protein is net neutral -> lowest point of solubility
also: Ca will associate with P groups, decrease solubility
38
the casein proteins are: (5)
```
as1
as2
B
gamma
kappa
```
39
The whey proteins are: (5)
```
a-lactalbumin
B-lactoglobulin
serum albumin
immunoglobulins
minor proteins
```
40
What is the proportion of caseins to whey?
83:`17
41
What are the major and minor caseins?
major: alpha and beta (23kDa)
minor: gamma and kappa, also lambda (derived from degradation of alpha or beta)
42
The major whey protein is:
beta-lactoglobulin (10% of total)
43
Caseins generally have high content of ______, but the major caseins lack what amino acid?
essential AA
| cysteine
44
How is kappa casein different from other caseins, and what important role does it play?
smaller than alpha or beta, with large CARBOHYDRATE MOIETY
less P, so less Ca binding
ESSENTIAL FOR MAINTAINING MICELLE STRUCTURE
protects other caseins (once hydrolyzed, other caseins will precipitate out)
45
Although overall, caseins act _____, they have some polar regions that are high in what?
non-polar
| phosphate, glutamate, aspartate
46
Caseins precipitate readily in high concentrations of ___, as _____. What is the exception?
Ca
Ca-caseinates
k-casein
47
What bond in k-casein, once hydrolyzed, will cause the degradation of the micelle?
Phe105 - Met106
48
Where do gamma and lambda caseins come from specifically?
gamma: from breakdown of as1 casein
lambda: from breakdown of B casein
49
What changes will cause milk micelles to revert to casein complexes, and eventually to soluble caseins?
lower pH, temperature, Ca
| higher P, citrate
50
k-casein usually forms a ____, due to ___ bonds between ___ residues.
trimer
disulfide
cysteine
51
How can you favor the creation of larger micelles?
high Ca , high temp
52
What factors will promote micelle formation?
raising temp, pH, Ca
| lower P, citrate
53
Casein micelles are associated with a lot of ____, and are held together by what bonds?
water (highly solvated)
```
Hydrophobic interactions
H bonds
electrostatic interaction (Ca -P bridges between P-Ser, P-Thr, Glutamic acid)
```
54
What are the products of chymosin (rennet) on kappa-casein? what are the fates of each?
cleaves between Phe105 and Met106 -> PARA-KAPPA-CASEIN, and a glycomacropeptide
para-k-casein will precipitate with Ca ions
glycomacropeptide stays in solution
55
What genetic modifications further increases cleavage rate of chymosin on kappa casein?
replace Met106 with Phe106 (increase by 80%!)
56
What acts as a bridge that allows binding between Serine, Threonine, and Glutamic acid residues in milk micelles?
Ca, Ca-phosphate
57
What is the second most abundant whey protein, and what is its function?
a-lactalbumin
| activates GALACTOSYL TRANSFERASE - enzyme for moving galactose from UDP galactose in golgi for LACTOSE SYNTHESIS
58
Where are immunoglobulins and serum albumin produced, and how are they added to milk?
Produced in liver
| added via bloodstream
59
Over half of the whey protein in cow milk is:
B-lactoglobulin (18kDa)
60
The whey protein ____ has a high MWt of 69kDa, and functions as _____.
BSA (bovine serum albumin)
| FFA carrier
61
The milk carbohydrates are:
```
lactose
lactose oligosaccharides (minor)
```
62
The types of immunoglobulins are:______.
| What is their general structure and purpose?
IgG1, IgG2, IgA, IgM
2 light chains, 2 heavy chains
provide calf with passive immunity
63
After heating milk at 95C for 20 min, and acidifying to pH 4.7, what remains in solution is known as:______. What are they?
proteose-peptones
| glycolytic enzymes, small proteins, etc
64
Free fatty acids in milk are bound to ____
BSA
65
lactose is about ____% of milk by weight
4-6%
66
The galactose in lactose is always in ____form
b-pyranose
67
What types of lactose are in milk? What are their differences?
alpha and beta
alpha: more stable, monohydrate form, glucose in a-pyranose form
beta: anhydrate form, higher solubility, more sweet, higher proportion at high processing temp, glucose in b-pyranose form
68
lactose is broken down by lactase, also known as _____. What are the products, and how does this affect taste?
beta-galactosidase
glucose and galactose
becomes sweeter
69
What vitamins are added to milk and why?
A: to make up for amount removed with fat (enrich)
D: to prevent deficiency (fortify)
70
Milk contains many helpful minerals, but:
also contains small amounts of harmful ones like Pb and As
71
What are some minor components in milk?
Vitamins
Minerals
Organic acids (lactic, orotic, citric, acetic)
hormones and GF
enzymes (catalase, lysozyme, aldolase, carbonic anhydrase)
72
How are caseins usually separated out?
acidification with acetic acid
73
What vitamins are highest in milk (soluble, and fat soluble)?
C and E
74
density is an important measure for milk because (2):
| What factors affect it?
- relate mass to volume (convert)
- estimate solids content
depends on composition (fat!) and temperature
75
What are some hormones found in milk?
```
Prolactin
thyroxine
estradiol
insulin
progesterone
growth hormone
```
76
What determines the value of milk?
fat content
77
Why is lactose useful for the pharmaceutical industry?
less sweet, used as a filler
78
What are some growth factors in milk?
IGF1, IGF2, transforming GF-a, transformin GF-b
79
Why must milk be processed to be sold?
risk of pathogens: M. bovis, Salmonella, E. coli
80
Describe the collection of milk for processing:
milk collected on farm -> cooled to 4.4C
delivered in insulated tank
mix with other milk within 2 days, or directly to processing plant
*maintain at 4.4C or below!
81
True/False: it is illegal to sell raw milk in Canada.
True
82
____ content in milk tends to stay constant, while ___ and ___ can vary.
protein; fat and lactose
83
What QC tests are necessary prior to processing? (5)
determine fat and total solids ($$$)
estimate sediment
microbiological tests (total, coliform, yeast, mold)
determine freeze point (see if any extra water)
assess flavor
84
What process is used to remove impurities? What impurities specifically?
clarification
sediment, animal cells, some bacteria
85
What could produce off-flavors in milk?
fat oxidation
fat lipolysis
animal feed used
absorption of odors
86
What types of heat treatment can be done on milk?
| Which is not applicable for milk to be drunk?
pasteurization (HTST or batch)
Thermization
UHT
Sterilization
Thermization is a sub-pasteurization process, meant for milk to be further processed into cheese
87
How does a clarifier work for milk?
centrifuge at high speed to separate out sediments. can use with hot or cold milk.
88
Heat is applied by _____ (3) for UHT processes.
heating coils, heating plates, or steam injection (then aseptic packaging)
89
Order the heat treatment methods for milk in increasing temperature.
Also order them in increasing time.
temp: thermization < HTST < sterilization < UHT
time: UHT < HTST < thermization < sterilization
90
Sterilization of milk is accomplished by heating in an ______.
autoclave
91
List the basic milk products in terms of increasing fat:
skim milk (fortify or unfortified) < partly skim < whole milk < half and half < light cream < heavy cream < butter
92
How does homogenization work?
milk forced through small opening, turbulence and shear force causes globules to break up into tiny globules < 1micrometer in diameter
creates a more stable emulsion
93
The two methods for gravitational fat removal from milk are:
shallow pan
| deep setting
94
What is the removal of fat from milk known as? What purpose does it serve?
Creaming
make low fat milk products
or use fat to make cream, butter
95
What are some further processed milk types?
filled milk (with added non-milk fat)
toned milk (added water or skim milk)
reconstituted milk (rehydrated milk powder)
lactose free (with lactase)
low sodium
flavored
canned (evaporated, condensed) - remove moisture, add sugar
96
Why is milk powder made?
as ingredient for further processing (formula, milk chocolate, etc)
for long shelf life, for countries with no dairy farming/refrigeration
97
What is the most common drying method for milk, and what are two alternatives?
spray drying
```
drum drying (normal or vacuum)
fluidized bed drying (using CO2 or N as foaming gas)
```
98
Once cream is removed from milk, what other products can be derived?
churn cream -> obtain butter and buttermilk
| can heat butter and clarify (remove milk solids) -> ghee
99
Does the drying process of milk affect the enzymes and proteins? What are the implications of this?
No; usually happens below 70C. Whey is not denatured, and enzymes are still active
so: enzymes can still cause oxidation and browning during storage
100
Once the cream is removed from unpasteurized milk, what other steps can be taken to produce other products? (3)
heat treatment
obtain pasteurized milk for drinking
or: acidify -> curd separation -> cheese and whey
or: add bacteria -> yogurt
101
What are some fermented dairy products? (4)
yogurt
buttermilk
sour milk
sour cream
102
Milk fat is used to produce: (3)
butter
cream
ice cream
103
Butter is a ______ emulsion, which is made possible by
```
water in oil
hydrophilic emulsifiers (lauroyl glutamate)
```
104
What are the 3 types of butter?
Sweet cream (from non-soured cream)
Cultured (from soured cream)
Soured (from non-sour cream, but fermented later)
105
Whipping cream should contain at least ___% fat. good quality cream should show volume increase of ___%, and not ____.
35%
80%
separate
106
Describe the butter making process:
churning: agitate milk/cream vigorously at 12-18C (so milk fat part solid, part liquid)
incorporates air -> whipped cream
continue agitation -> becomes more coarse, eventually semi-solid fat granules will separate from liquid phase
(butter and buttermilk)
107
What is a typical ice cream formulation?
66% water, 14% sucrose, 11% non-fat milk solids, 10% milk fat, 2% glucose syrup, and small amounts of stabilizers(emulsifiers) and thickeners (polysaccharides)
also: flavorings and colors
108
What is overrun, and how is it calculated? What is the usual amount?
increase in volume of ice cream due to whipping in air
100x (final volume - initial volume)/initial volume = % overrun
usually 70-100% (volume about doubles)
109
At what stage in ice cream making are the other add-ins (fruits, nuts, etc) added?
soft ice cream stage (before hardening)
110
Describe the steps of ice cream production: (6)
1. components mixed
2. ice cream mix pasteurized (batch or HTST)
3. high pressure homogenization
4. cooled to increase viscosity (4.4C)
5. cooled while mixing in air (-5.5C)
6. semi-solid ice cream put in package, cooled to -34C (hardening)
111
What causes the sour taste of fermented milk products?
lactic acid from lactic acid bacteria metabolic activity
112
What are some common LABs?
lactobacillus, lactococcus, leuconostoc, pediococcus, streptococcus
113
What are the 2 types of fermentation that occur, and what determines what type will take place?
homofermentative: only produce lactic acid
heterofermentative: produces other byproducts as well (acetic acid, ethanol, CO2)
depends on bacteria type - different enzymes and pathways. homo uses glycolytic only, while hetero use pentose phosphate pathway
(both act on carbohydrates)
114
the lactic acid produced in milk can be either _____ or ______. Which one should be limited in the diet and why?
L enantiomer, D enantiomer
| limit D: not normally produced in humans so not metabolized well
115
How is soured buttermilk made?
add S. lactis to skim or part skim milk -> thick, sour, bubbly product
116
Why does thickening and curdling occur in fermented milk products?
increased acidity will cause coagulation of caseins
117
What non-bacteria microbe is used to produce kefir, and what is the result?
yeast (torula)
| some alcohol content, contains "grains" made of clotted milk and yeast bodies
118
After the production process for fermented milk products is complete, what should take place?
heat to kill microbes
| or keep at cool temperatures to slow growth (active culture)
119
How is the casein separated from whey for cheese making?
acid/rennet used to cleave kappa casein -> will precipitate with Ca, allows other caseins to coagulate with Ca and heat -> forms curd
120
The 3 basic steps of cheese production:
curdle milk
remove whey
ripening of curd (add microflora)
121
What steps take place before the actual curdling of cheese? (2)
```
standardize protein and fat content
additives added (lysozyme, nitrates, Ca)
```
122
what are some classification methods for cheese? (4)
source of milk (cow, goat, etc)
moisture/hardness (soft, semi-soft)
fat content
curdling method (acid vs rennet)
123
How do enzyme coagulation and acid coagulation of milk differ?
enzyme: use rennet/chymosin
acid: require combination with heat. use starter culture or add acid directly.
Acid method has higher protein recovery
124
After the curd has formed, what steps are taken?
cut and heated gently, cubes will shrink and expel whey
| then removed from whey
125
What will determine the final pH of the cheese?
the final moisture in the curd (determines the amount of FERMENTABLE LACTOSE)
126
What happens during cheese ripening?
bacteria, mold, yeast, and milk enzymes will degrade proteins, fat, and lactose -> produce flavor and texture changes
127
What causes the shrinking of curd when heated? What other effect happens?
increased hydrophobic interactions -> shrinks protein matrix -> syneresis
also: more lactic acid produced (fermentation rate increased)
128
the qualities of the final cheese will depend on what factors for ripening conditions? (4)
microbial content
humidity
temperature
biochemical composition of curd
129
Why would removing citrate help to increase coagulation of caseins?
Normally citrate has a chelating effect; removing it allows caseins to coalesce together
130
Where are enzymes for cheese making sourced? (4)
Chymosin/Pepsin: from animal stomachs
plant enzymes
proteinases from microbes
or genetically modify microbes to produce rennet
131
added ___ and ___ will increase the firmness of the curd.
Ca; P
132
What are the 2 types of starter cultures, and what are the 3 important characteristics they should have?
mesophilic (20-40C) or thermophilic (up to 45C)
1. produce lactic acid
2. break down protein (ripening)
3. make CO2 (for some cheeses, holes)
133
Why is lactic acid production important for cheese? (3)
- initial curdling
- contraction of curd -> squeeze out whey
- LAB suppresses other undesirable microbes
134
proteolysis during the ___ stage is caused by proteases from ____(3), and produces:
ripening
milk, bacteria culture, added enzymes
flavor and aroma compounds
135
Lactic acid production will stop when:
heat is applied (kill bacteria)
| or all lactose used up
136
What bacteria is used to make holes in swiss cheese? How does this work?
What is sometimes done as an alternative?
propionic acid bacteria
convert lactic acid -> propionic acid, acetic acid, CO2
CO2 is dissolved, but once becomes saturated will produce bubbles -> forms holes in ripening curd
can also directly inject CO2 (faster, lower pH)
137
What additive is included in small quantities to prevent clostridium?
When is it not needed?
saltpeter (NaNO3 or KNO3) - nitrates
| if milk is microfiltered, then this is not necessary (or less is needed)
138
Aside from nitrates, what other additives are included in cheese sometimes, and what are their purposes? (2)
CaCl2 - increase firmness of curd
| Na2PO4 - add before CaCl2, to increase elasticity (esp in low fat cheese)
139
How is salt applied to cheese? (2)
dry salting
| brining
140
Salt will affect: (3)
consistency
taste
bacterial processes
141
addition of salt to cheese will cause______ due to ______(2).
expelling more moisture
| osmotic pressure, precipitate out whey proteins (salting out)
142
What is the final treatment for curd after whey is removed? (2)
1. moulding (either put in mould directly, or first press into blocks and cut to size)
2. pressed (pneumatic/hydraulic presser) - expel more whey, develop texture
143
Why would color agents be added to cheese, and what are some common examples? (3)
for appearance, and to correct for seasonal variations in color of milk fat
```
carotene, orleana (seasonal variations)
green chlorophyll (make paler blue cheeses)
```
