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Food Chemistry - FDSC251 > U8 > Flashcards

U8 Flashcards

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1
Q

what protein source has the best nutritive value in terms of amino acid balance

A

egg

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2
Q

how are milk proteins categorized

A

casein and whey

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3
Q

casein

A

isoelectric point 4.5 - isolated when milk’s pH has this value

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4
Q

whey

A

left in solution after casein removed

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5
Q

when is casein insoluble

A

in weakly acidic media - 4.5

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6
Q

what kind of protein is casein

A

phosphoprotein

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7
Q

where is the phosphate attached in casein

A

serine amino acid

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8
Q

what are submicelles

A

aggregates of the casin fractions (a,b,g,k)

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9
Q

what are micelles

A

aggregates of submicelles, hydrophobic on the inside and hydrophilic k-casein on the outside

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10
Q

what do micelles protect from happening

A

coagulation into curds - cheese production

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11
Q

what are serum caseins

A

monomers of casein - rare

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12
Q

what does the extent of aggregation depend on

A

ca concentration and pH

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13
Q

what precipitates in the presence of casein and what doesnt

A

k casein doesnt, everything else does

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14
Q

when are micelles formed

A

only in the presence of Ca. can break and reform depening on levels

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15
Q

why is milk white and opaque

A

micelles cause light scattering

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16
Q

true or false: micelles are solvated and porous

A

true! k-casein is polar, so till attract water

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17
Q

how are rennin and chymosin differen

A

theyre not silly

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18
Q

where is rennin from

A

the 4th stomach of a suckling calf

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19
Q

how does rennin/chymosin work

A

it targets the 105-phe and 106-met peptide bond, cleaving it and resulting in para-k-casein and glycomacroprotein

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20
Q

what happens when para-k-casein is formed

A

it isn’t soluble, so it precipitates with the other hydrophobic caseins, coagulating and forming a curd

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21
Q

is glycomacroprotein soluble or insoluble

A

soluble - stays

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22
Q

a-1-casein: phosphoserine

A

8 phosphoserine residues, centralized in 43-80AAs with 12 carboxyl groups - polar region

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23
Q

a-1-casein: self-associating tendency

A

due to hydrophobic side chains in residues 100-199

24
Q

a-1-casein: proline

A

distributed all along chain

effects: no crystallization and hindered secondary structure

25
Q

what happens to a-1-casein in the presence of Ca

A

forms in insoluble ca-salt

26
Q

how does the molecular structure of alpha-2-casein effect its properteis

A

dipolar - cationic C and anionic N

27
Q

which precipitates more easily, alpha1casin or alpha2casein

A

alpha2casein

28
Q

which casein is the most hydrophobi

A

b

29
Q

b casin phosphoserines

A

5 localized in1-40 range

30
Q

where are the ionizable sites in b casein

A

1-40 range

31
Q

where are the nonpolar sites in b

A

139-209

32
Q

where are beta sheets created in the chain and why do we know this

A

a-periodic part. in response to higher temperatures, there are more b sheets but no decrease in a helix

33
Q

where are the cysteines in b

A

none

!

34
Q

does b self-associate

A

no

35
Q

at what level of ca does b casein precipitate

A

milk-levels

36
Q

what are gamma caseins

A

degraded b-caseins

37
Q

molecular structure of k-casein

A

horse and rider model

38
Q

n terminus of k-casin

A

hydrophobic - interacts with other casein

39
Q

when is the monomer of k-casein accessible and what is it

A

only under reducing conditions. it is 2 cysteine residues

40
Q

why does k-casein self-associate

A

forms disulfide bonds between cys

41
Q

how does k-casein protect the other caseins

A

Aggregates with the other caseins to prevent their coagulation in the presence of Ca ions – forms stable casein complexes and casein micelles

42
Q

what are the hairs on k-casein

A

hydrophilic c-terminal domain

43
Q

what is acid coagulation

A

addition of acids or lactic acid fermentation to change the pH to 4.2-4.6

44
Q

what is the most prevalent protien in whey? 2nd most?

A
  1. b-lactoglobulin

2. a-lactalbumin

45
Q

what is the difference between the A and B variants of b-lactoglobulin

A

a- aspartic acid

b-glycine

46
Q

how many disulfide bonds and free sulfhydryl groups in b-lactoglobuion

A

2 disulf

1 free sulfhydryl

47
Q

when does the b-lactoglobulin exist as a monomer

A

pH lower thand 3 or higher than 8

48
Q

when does the lactoglobulin exist as an octamer

A

3.1-5.1 pH

49
Q

when is it a dimer

A

any other pH

50
Q

why does the b-lactoglobulin oligoerize

A

carboxyl groups

a variant forms more readily

51
Q

how many disulfide links in a-lactalbumin

A

4

52
Q

what enzyme does a-lactalbumin effect

A

galactosyl transferase

53
Q

what is different about a-lactalbumin’s heat sensitivity

A

more stable when in the presence of calcium

54
Q

how does bovine serum albumin enter milk

A

through the blood stream, not made in the mammary gland

55
Q

what are hydrolysates

A

made by enzymatic treatment of whey protein isolates - broken down proteins into smaller portions

Food Chemistry - FDSC251 (10 decks)

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