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2) Food Chemistry I > Proteins III > Flashcards

Proteins III Flashcards

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1
Q

__________ contains 12% solids, of which 3.5 is protein

A

Fluid milk

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2
Q

Milk proteins have high nutritive value (good AA balance), surpassed only by ____________ which are a good source of ___________

A

egg albumin

lysine

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3
Q

Milk proteins can be categorized into two groups: ________ and _______ proteins

A

caseins

whey

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4
Q

__________ is a general term for milk proteins having an isoelectric point at pH 4.5

A

Casein

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5
Q

________ are isolated by adjusting the pH of milk to 4.5 by using acid, while _________ are left in solution

A

Casein

whey

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6
Q

What are the most common caseins?

A
  • As1-casein

- B-casein

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7
Q

What is the most common whey protein?

A

B-Lactoglobulin

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8
Q

O. Hammarsten (1877) outlined a procedure to separate ______, _______, and _________

A

casein
lactalbumin
lactoglobulin

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9
Q

Skim milk is diluted, and then acidified with ________; ________ flocculates, while the ______ proteins stay in solution

A

acetic acid
casein
whey

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10
Q

Established that ______ is insoluble in weakly acidic media

A

casein

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11
Q

Casein is a ____________ with the phosphate attached to _______

A

phosphoprotein

serine

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12
Q

Classify the types of casein in order of most present to least present.

A

as1 > B > K > as2 > γ

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13
Q

____ and ____ casein are differentiated from each other by their sensitivity to the presence of Ca2+ ions

A

as1

K

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14
Q

____ casein will precipitate in the presence of Ca2+, while ____ casein does not

A

as1

K

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15
Q

Micelles dissociate if _____ is dialyzed from the solution, and will reform if ____ is added back

A

Ca2+

Ca2+

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16
Q

_________ are responsible for the opaque whiteness of milk, an optical effect due to light scattering (properties from casein)

A

Micelles

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17
Q

The opaque whiteness of milk is due to ____________

A

light scattering of casein micelles

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18
Q

Calcium sensitive ____ is surrounded by _____

A

as1 casein

K casein

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19
Q

Paracasein is another form of casein that is obtained by _________

A

rennin

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20
Q

______ is a proteolytic enzyme obtained from the ____ stomach of the calf

A

Rennin

fourth

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21
Q

Rennin attacks ______ at a specific site, cleaving off a ____________________

A

K-casein

glycomacropeptide

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22
Q

When ______ is added into a milk solution, the micelles are destabilized and they associated to form a curd, which forms ______________

A

rennin

paracasein

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23
Q

The formation of ___________ is the first step in cheese making

A

paracasein

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24
Q

Acid/Isoelectric casein and paracasein are similar physically because they aren’t ________________

A

temperature sensitive

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25
Q

In the __ variation of as1 casein, AA residues 14-26 are missing

A

A

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26
Q

In the __ variation of as1 casein, the peptide chain has 199 AA residues

A

B

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27
Q

In the __ variation of as1 casein, Glu-192 is replaced by Gly-192

A

C

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28
Q

In the __ variation of as1 casein, Ala-53 is replaced by phosphothreonine

A

D

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29
Q

All the variations of ___________________ contain 8 phosphoserine residues, 7 of which are localized between 43 and 80

A

as1-casein

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30
Q

________ contains a portion with 12 carboxyl groups from _____________ and _____________ residues, making it extremely ______

A

as1-casein
glutamic acid
aspartic acid
polar

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31
Q

In _______, AA 100-199 are _______ and responsible for the self-association tendencies of the protein despite the repulsive forces between the _________ groups, and the lack of ___________ residues

A

as1-casein
apolar
phosphate
cysteine

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32
Q

The ________ residues distributed along the chain in as1 casein hinders the ordered structure

A

proline

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33
Q

In as1-casein, the hydrophilic segment is connected to a____________

A

hydrophobic B-sheet region

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34
Q

In as1-casein, the hydrophobic B-sheet region is connected to the region that contains the ____________, which is connected to a short ________

A

phosphate

a-helical segment

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35
Q

In as1-casein, the a-helical segment is connected to a very hydrophobic ______________ domain, which contains extended __________

A

carboxy-terminal

B-strands

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36
Q

The carboxy terminal segment of as1-casein is very ____________

A

hydrophobic

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37
Q

In as1-casein, - 15% of the peptide chain is _________, and 22% has a ____________

A

a-helical

B-structure

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38
Q

__________ consists of 207 AA residues

A

as2-casein

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39
Q

___________ has a pronounced dipolar structure due to the concentration of _______ groups in the region of the N-terminal, and ________ groups in the region of the C-terminal

A

as2-casein
anionic
cationic

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40
Q

______ contains 11 phosphoserine and 2 cysteine residues

A

as2-casein

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41
Q

________ precipitates with Ca2+ more easily than as1-casein

A

as2-casein

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42
Q

______ is the most hydrophobic casein

A

B-casein

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43
Q

_______ has 209 AA residues (A-variant)

A

B-casein

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44
Q

___________ contains 5 phosphoserine residues that are localized between 1 and 40, which contains practically all the __________ sites of the molecule

A

B-casein

ionizable

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45
Q

In B-casein, 136-209 contain residues with _______ side chains

A

apolar

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46
Q

Which casein acts like soap?

A

B-casein

Polar head and an apolar tail

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47
Q

______ contains 9% a-helical structure and 25% B-structure

A

B-casein

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48
Q

In B-casein, - increasing the temperature results in an increase in _____________, with no decrease in ____________ content

A

B-structure

a-helical

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49
Q

In B-casein, the ___________ originates in an aperiodic part of the chain

A

B-structure

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50
Q

Like _______-casein, _______-casein contains no cysteine residues

A

as1

B

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51
Q

Unlike _____-casein, ______-casein does not self-associate spontaneously

A

as1

B

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52
Q

________-casein precipitates in the presence of Ca2+ ions found in milk

A

B-casein

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53
Q

When _______-casein precipitates with Ca2+, at temperatures of < 1oC, the calcium salt is quite soluble

A

B

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54
Q

A1 and A2 B-casein are genetic variants of _______ that differ only by one amino acid

A

B-casein

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55
Q

Company marketing with predominantly __ protein claims that milk containing __ proteins are harmful, but there is insufficient evidence to prove

A

A2

A1

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56
Q

_________ are degradation products of B-casein formed by milk proteases

A

gamma-casein

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57
Q

________-casein has 169 residues

A

K

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58
Q

_____-casein is a monomer

A

K

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59
Q

____-casein contains 2 cysteine residues, and is only accessible under reducing conditions

A

K

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60
Q

Normally, __-casein occurs as a trimer or as higher oligomers by the formation of ________bonds

A

K

disulfide

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61
Q

In ___-casein, varying amounts of carbohydrate are bound to the peptide chain through Threonine residues at positions 131, 133, 135, or 136 (A variant)

A

K

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62
Q

___-casein can be separated electrophoretically into various components that have the same AA composition, but differ in the carbohydrate content

A

K

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63
Q

Which casein has a 3D horse and rider model?

A

K

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64
Q

In the horse and rider model of __-casein, the ___-terminal makes up the horse, the ____-terminal makes up the rider, and the two legs of the horse are made of _______

A

K
N
C
B-structures

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65
Q

___-casein contains 16% a-helical structure and 27% B-structure

A

K

66
Q

In the horse and rider model of __-casein, the legs are very _____________ and are an area of interaction with other caseins

A

K

hydrophobic

67
Q

____-casein is the only constituent of casein that remains soluble in the presence of Ca2+ ions in milk

A

K

68
Q

Aggregation of ____-casein and ____-casein with ____-casein prevents their coagulation in the presence of Ca2+ ions

A

as1
B
K

69
Q

10% of the total casein fraction is present in milk as _________, usually designated as _______ caseins

A

monomers

serum

70
Q

A(n) _______ in H+ and Ca2+ promotes casein micelle formation

A

increase

71
Q

A(n) _________ in citrate promotes casein micelle formation

A

decrease

72
Q

A(n) _________ in phosphate promotes casein micelle formation

A

decrease

73
Q

A(n) _________ in temperature promotes casein micelle formation

A

increase

74
Q

Dialysis of casein complexes against a ___________ (citrate, phosphate) would shift the equilibrium completely to _________

A

chelating agent

monomers

75
Q

The diameter of micelles has a mean of ______

A

150 nm

76
Q

Micelles are held together by _______, ________, and ________

A

hydrophobic interactions
electrostatic interactions
hydrogen bonds

77
Q

In the case of casein micelles, _______________ are minimal at temperatures below 5oC

A

hydrophobic interactions

78
Q

The electrostatic interactions in casein micelles are mostly between ________ and ________ that form bridges between __________ and ________ residues

A

calcium
calcium phosphate
phosphoserine
glutamic acid

79
Q

What are the two types of subunits of casein micelles?

A

Contains K-casein

Does not contain K-casein

80
Q

_________ are arranged on the surface of submicelles

A

K-casein molecules

81
Q

The ________ C-terminals of K-casein protrude from the surface, which prevents further aggregation

A

hydrophilic

82
Q

The hydrophilic _________ of K-casein prevent further aggregation

A

C-terminal

83
Q

Aggregation of the submicelles proceeds until the entire surface of the forming micelle is covered with ________

A

K-casein

84
Q

_______ is 5 nm thick

A

K-casein coverage

85
Q

A small part of _______ is also found inside the micelle

A

K-casein

86
Q

______ has a role in stabilizing casein micelles

A

K-casein

87
Q

Due to its role in stabilizing casein micelles, cleaving of _______ causes the casein proteins to __________, and separate from the whey

A

K-casein

coagulate

88
Q

Rennet contains the precursor of the enzyme _________, an acid protease having specificity for __________

A

chymosin

K-casein

89
Q

________ specifically recognizes the sequence from His-98 to Lys-11 in _______, and selectively cleaves the peptide bond between Phe-105 and Met-106

A

Chymosin

K-casein

90
Q

Chymosin cleaves K-casein into ___________ and a ___________

A

para-K-casein

glycomacropeptide

91
Q

Chymosin releases a soluble ___________ while the __________ precipitates in the presence of Ca2+ ions

A

glycomacropeptide

para-K-casein

92
Q

What are the two largest components of whey protein?

A
  • B-lactoglobulin (10%)

- B-lactalbumin (2%)

93
Q

________ is 10% of the total milk protein, and 58% of the ____ protein fraction

A

B-lactoglobulin

whey

94
Q

_____ has 162 AA

A

B-lactoglobulin

95
Q

In B-lactoglobulin, ___ variant has an aspartic acid, while the ___ variant has a glycine

A

A

B

96
Q

_____ contains 2 disulfide bonds, 1 free sulfhydryl group, and no phosphorus

A

B-lactoglobulin

97
Q

Which milk protein has a dynamic disulfide bond?

A

B-lactoglobulin

98
Q

Below pH 3.0 and above pH 8.0, __________exists as a ______

A

B-lactoglobulin

monomer

99
Q

Between pH 3.1 and 5.1, at low temperatures and high concentration, B-lactoglobulin associates to form an _______

A

B-lactoglobulin

octomer

100
Q

Which milk protein can oligomerize?

A

B-lactoglobulin

101
Q

This oligomerization is mediated through ______ groups

A

carboxyl

102
Q

The ___ variant of B-lactoglobulin forms more readily than the ___ variant since it has an extra ______ group

A

A
B
carboxyl

103
Q

At the pH of milk, _________ tends to form a ______

A

B-lactoglobulin

dimer

104
Q

The _______ of __________ are spherical with diameters of about 18 angstroms

A

dimers

B-lactoglobulin

105
Q

The _______ structure of B-lactoglobulin is homologous to that of ____-binding proteins

A

secondary

retinol

106
Q

The secondary strand of ___________ contains 9 strands of B-structure

A

B-lactoglobulin

107
Q

Which milk protein associates to form a barrel with _______ and a lid with _______?

A

B-lactoglobulin
B-structures
a-helix

108
Q

The center of the barrel of _______ is hydrophobic and is involved in the binding of hydrophobic molecules

A

B-lactoglobulin

109
Q

The biological role of B-lactoglobulin, manufactured in the __________, is _________

A

mammary gland

unknown

110
Q

B-lactoglobulin is effective at binding __________

A

retinol

111
Q

__________’s _________ pocket is effective at binding retinol

A

B-lactoglobulin

hydrophobic

112
Q

It is speculated that the binding of ________ may have a regulatory role in the mammary gland

A

vitamin A

113
Q

Because of its prevalence in bovine milk, the properties of whey protein in the food industry are largely the properties of _______________

A

B-lactoglobulin

114
Q

___________ compose 2% of total milk protein and 13% of total whey protein

A

a-Lactalbumin

115
Q

____ has 123 AA

A

a-Lactalbumin

116
Q

________ has 4 disulfide linkages and no phosphate groups

A

a-Lactalbumin

117
Q

__________ modifies the activity of galactosyl transferase

A

a-lactalbumin

118
Q

a-lactalbumin modifies the activity of _______________

A

galactosyl transferase

119
Q

The transfer of UDP-galactose to N-acetylglucosamine groups (glucose) is slow without __________________

A

a-lactalbumin

120
Q

________________ adds UDP-galactose to glucose and produces _______ and UDP, which is faster when __________ is attached

A

galactosyl transferase
lactose
a-lactalbumin

121
Q

40% of the residues of the AA sequences of _____________and _____________ are the same, including the cysteine residues, and 20% of the residues are similar

A

a-lactalbumin

lysozyme

122
Q

a-lactalbumin is related to ________

A

lysozyme

123
Q

________ helps synthesize the linkage that _________ cleaves

A

a-lactalbumin

lysozyme

124
Q

Do a-lactalbumin and lysozyme work on the same substrates?

A

No

125
Q

Most proteins are (more/less) stable in the presence of calcium due to the ability of calcium to promote the formation of __________________ with most proteins

A

less

ionic intermolecular cross-links

126
Q

Ionic intermolecular cross-links between proteins and calcium hold the molecules in proximity and increases ____________________

A

the likelihood of aggregation upon heating

127
Q

____________ is unusual since the molecule is more stable to heat in the presence of calcium

A

a-lactalbumin

128
Q

a-lactalbumin uses calcium to form _________________ bonds that tend to make the molecule resistant to thermal unfolding

A

intramolecular ionic

129
Q

Milk protein that is more stable to heat in the presence of calcium: ____________

A

a-lactalbumin

130
Q

Bovine Serum Albumin isolated from milk is identical to BSA from ___________

A

blood serum

131
Q

Where is bovine serum albumin synthesized?

A
  • Not synthesized in the mammary gland

- Enters milk through the bloodstream

132
Q

_________ has 17 disulfide linkages, 1 free sulfhydryl group, and no phosphorus

A

Bovine Serum Albumin

133
Q

In blood plasma, _______ is a carrier of free fatty acids

A

albumin

134
Q

Which molecule binds hydrophobic molecules in milk?

A

albumin

135
Q

________ and ________ are used in the manufacture of paper for coating to improve the adhesion of ink to the surface, in waterproof glue, to make fabrics water-repellent, etc.

A

Caseins

caseinates

136
Q

_______ is recovered by coagulation, achieved by _______ or _______ treatment

A

Casein
acidification
enzymatic

137
Q

Acid coagulation of casein is achieved by ________________ or by direct addition of acids to the milk at 35-50oC to attain a pH of 4.5

A

lactic acid fermentation

138
Q

_________ coagulation is achieved at 45oC, while _________ coagulation is achieved from 35-50oC

A

Enzymatic

acid

139
Q

To terminate enzymatic coagulation, the milk is ___________

A

heated to 65oC to inactivate the enzyme

140
Q

Following coagulation of casein, it is separated from the milk in a ___________, _____, and ______

A

sedimentation centrifuge
washed
dried

141
Q

Enzymatic coagulation produces ________, while acid coagulation produces ________

A

rennet casein

acid casein

142
Q

To produce a casein product that is soluble or readily dispersible, the casein is dispersed in ______ and treated with ______ at 90oC and pH 6.2-6.7

A

water

alkali

143
Q

What is the product of casein solubilization?

A

Sodium caseinate or calcium caseinate

144
Q

Following its solubilization, sodium caseinate is ________

A

spray-dried

145
Q

______ is considered valueless since it is too high in salt to be consumed in large amounts

A

Whey

146
Q

Spray-dried _____ and ___ products are used in formula, baked goods, candies, beverages, and animal feed

A

whey

whey

147
Q

(WPC/WPI) contain less protein than (WPC/WPI)

A

WPC

WPI

148
Q

How is whey usually dried? What is a technique that can reduce the cost?

A
  • Spray drying

- Reverse osmosis

149
Q

Reverse osmosis is used for the drying of ________, using a ___________ that holds back _____________

A

whey
perm-selective barrier
proteins, lactose, salt

150
Q

In __________ the pressure exceeds the osmotic pressure

A

reverse osmosis (hyperfiltration)

151
Q

Whey protein concentrates are produced by ____________

A

ultrafiltration

152
Q

What does ultrafiltration allow to pass through?

A

Lactose, salt, water

Holds back proteins

153
Q

The amount of lactose removed in whey processing depends on the ___________ and _____________

A

the number of ultrafiltration stages

the amount of wash water

154
Q

Which method is highly detrimental to whey?

A
  • Steam injection
  • Precipitation of the denatured proteins
  • Sedimentation centrifuge
  • Drying
155
Q

For the recovery of _____ from whey protein concentrations, the filtrate obtained in the _________ step can be concentrated by _________using a membrane the selectively holds back the lactose while allowing the ____ to pass through

A

lactose
ultrafiltration
reverse osmosis
salts

156
Q

The lactose concentrate recovered from reverse osmosis is _____ and cooled slowly to induce ____________

A

seeded

sugar crystallization

157
Q

Lactose can be recrystallized to yield a _________, which is used as a ________

A

raffinate

filler in tablets

158
Q

___________ require extensive processing (ultrafiltration, microdialysis, and ion exchange) to obtain a highly-purified protein

A

WPI

159
Q

___________ are produced by the enzymatic treatment of WPI to break the proteins into peptides that are more easily digested, while the nutritional quality of the protein remains high

A

Whey protein hydrolysates

160
Q

____________ are less likely to trigger allergic reactions than _________________; they are used often in infant formulas

A

Whey protein hydrolysates

non-hydrolyzed whey protein

2) Food Chemistry I (31 decks)

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