P3. Milk proteins
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7 common sources of proteins?
• milk • meat • eggs • fish • cereals • soybean • pulses (pea, lentil, chickpea)
each protein system is _________ and its properties also depend on what? (2)
• unique • processes used to extract or isolate it
fluid milk contains __% solids, of which ___% is protein
12% solids - 3.5% proteins
milk proteins have high _________ value (what does it mean?), surpassed only by ____ _________ and are a good source of ________ (an _________ aa)
• nutritive value (good aa balance) • by egg albumin • lysine (essential aa)
2 groups of milk proteins?
• casein • whey proteins
_________ is a general term for milk proteins and have an isoelectric point at pH _____ –> isolated by adjusting pH of milk to _____ using _______ - proteins left in solution are termed ______ proteins
• casein • 4.5 • 4.5 using acid • whey
% of total milk protein: - caseins - whey proteins
• casein: 83% • whey proteins: 17%
what are the main types of casein in order of highest to lowest percentage of caseins?
• a(s1) = 44% • b = 25% • k (kappa) = 14% • a(s2) = 11% • y (gamma) = 5%
main types of “whey proteins” in order of highest to lowest percentage?
• beta-lactoglobulin = 58% • a - lactalbumin = 13% • immunoglobulin = 12% • minor proteins = 12% • serum albumin
which whey protein are 7% of population allergic to?
beta-lactoglobulin
in 1877, O Hammarsten distriguished (how many) proteins in milk: name them
• 3! • casein + lactalbumin +lactoglobulin
O Hammarsten outlined the following procedure for the isolation of casein: (2 steps ish)
• skim milk is diluted, then acidified with acetic acid • casein flocculates, while whey proteins stay in solution
specific property of casein: it is __________ in ______ _______ media
insoluble in weakly acidic media
casein was subsequently established to be a ___________ with _______ being attached to the aa ________
• phosphoserine • phosphate being attached to serine
in 1939, casein was shown by _________ to consist of 3 fractions: ?
• electrophoresis • alpha, beta and kappa
how are different types of casein differentiated? (3 ish)
• isoelectric point • molecular weight (different aa sequence) • phosphorus content
North American cows have which variants?
A and B (vs C and D are more Australian)
y-casein are the products of proteolysis of __________
beta-casein
in milk, most of casein proteins are present in _________ particles called ________ __________
• colloidal particles • casein micelles
casein micelles are responsible for the ________ ______________ of milk, an optical effect due to ______ ___________
• opaque whiteness of milk • due to light scattering
micelles are very complex structures: ____________ assemblies made up of the different _______ _________
• supramolecular assemblies • different casein fractions
casein micelles __________ if Ca2+ is dialyzed from solution –> will reform if Ca2+ is ??
• dissociate • if Ca2+ is added back
what is a submicelle? vs a micelle?
• submicelle: 1 b + 1 a(s1) + 1 a(s2) + 1 k –> 10 nm • micelles = lots of submicelles together –> 20-300 nm
alpha (s1) - casein: - how many aa? - which aa distributed all along peptide chain –> hindering formation of ? - contain ___ phosphoserine residues - how many phosphoserine residues localized btw positions ____ and _____ –> this portion also contains 12 ? = very _________ - aa 100-199 are _______ = responsible for ?
• 186-199 aa • proline –> hinder formation of ordered structures • 8 phosphoserine residues • 7 localized between 43 and 80 –> also contains 12 carboxyl groups (glutamic and aspartic residues) = extremely polar • apolar = responsible for strong self-association tendencies of a(s1)-casein/hydrophobic interactions (despite repulsive forces btw phosphate groups and lack of cysteine residues)