U8 Flashcards
what protein source has the best nutritive value in terms of amino acid balance
egg
how are milk proteins categorized
casein and whey
casein
isoelectric point 4.5 - isolated when milk’s pH has this value
whey
left in solution after casein removed
when is casein insoluble
in weakly acidic media - 4.5
what kind of protein is casein
phosphoprotein
where is the phosphate attached in casein
serine amino acid
what are submicelles
aggregates of the casin fractions (a,b,g,k)
what are micelles
aggregates of submicelles, hydrophobic on the inside and hydrophilic k-casein on the outside
what do micelles protect from happening
coagulation into curds - cheese production
what are serum caseins
monomers of casein - rare
what does the extent of aggregation depend on
ca concentration and pH
what precipitates in the presence of casein and what doesnt
k casein doesnt, everything else does
when are micelles formed
only in the presence of Ca. can break and reform depening on levels
why is milk white and opaque
micelles cause light scattering
true or false: micelles are solvated and porous
true! k-casein is polar, so till attract water
how are rennin and chymosin differen
theyre not silly
where is rennin from
the 4th stomach of a suckling calf
how does rennin/chymosin work
it targets the 105-phe and 106-met peptide bond, cleaving it and resulting in para-k-casein and glycomacroprotein
what happens when para-k-casein is formed
it isn’t soluble, so it precipitates with the other hydrophobic caseins, coagulating and forming a curd
is glycomacroprotein soluble or insoluble
soluble - stays
a-1-casein: phosphoserine
8 phosphoserine residues, centralized in 43-80AAs with 12 carboxyl groups - polar region
a-1-casein: self-associating tendency
due to hydrophobic side chains in residues 100-199
a-1-casein: proline
distributed all along chain
effects: no crystallization and hindered secondary structure
what happens to a-1-casein in the presence of Ca
forms in insoluble ca-salt
how does the molecular structure of alpha-2-casein effect its properteis
dipolar - cationic C and anionic N
which precipitates more easily, alpha1casin or alpha2casein
alpha2casein
which casein is the most hydrophobi
b
b casin phosphoserines
5 localized in1-40 range
where are the ionizable sites in b casein
1-40 range
where are the nonpolar sites in b
139-209
where are beta sheets created in the chain and why do we know this
a-periodic part. in response to higher temperatures, there are more b sheets but no decrease in a helix
where are the cysteines in b
none
!
does b self-associate
no
at what level of ca does b casein precipitate
milk-levels
what are gamma caseins
degraded b-caseins
molecular structure of k-casein
horse and rider model
n terminus of k-casin
hydrophobic - interacts with other casein
when is the monomer of k-casein accessible and what is it
only under reducing conditions. it is 2 cysteine residues
why does k-casein self-associate
forms disulfide bonds between cys
how does k-casein protect the other caseins
Aggregates with the other caseins to prevent their coagulation in the presence of Ca ions – forms stable casein complexes and casein micelles
what are the hairs on k-casein
hydrophilic c-terminal domain
what is acid coagulation
addition of acids or lactic acid fermentation to change the pH to 4.2-4.6
what is the most prevalent protien in whey? 2nd most?
- b-lactoglobulin
2. a-lactalbumin
what is the difference between the A and B variants of b-lactoglobulin
a- aspartic acid
b-glycine
how many disulfide bonds and free sulfhydryl groups in b-lactoglobuion
2 disulf
1 free sulfhydryl
when does the b-lactoglobulin exist as a monomer
pH lower thand 3 or higher than 8
when does the lactoglobulin exist as an octamer
3.1-5.1 pH
when is it a dimer
any other pH
why does the b-lactoglobulin oligoerize
carboxyl groups
a variant forms more readily
how many disulfide links in a-lactalbumin
4
what enzyme does a-lactalbumin effect
galactosyl transferase
what is different about a-lactalbumin’s heat sensitivity
more stable when in the presence of calcium
how does bovine serum albumin enter milk
through the blood stream, not made in the mammary gland
what are hydrolysates
made by enzymatic treatment of whey protein isolates - broken down proteins into smaller portions