ASRB NET and ARS: dairy disciplines · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersCaseins and the casein micelle, whey proteins, minor proteins, genetic variants, heat denaturation, and the indigenous milk enzymes used as process indicators.
In the exams: ICAR AICE subject 34 Unit 2; ICAR AIEEA-PG group 16; ASRB NET Dairy Chemistry
ASRB NET and ARS — Dairy Chemistry
Master's-level recall: protein fractions and their calculation from nitrogen data, micelle composition, variant differences including A1 and A2 beta-casein, whey protein structure, indigenous enzymes and bioactive peptides.
How our questions for ASRB NET and ARS spread across the units of Milk Proteins & Enzymes. Difficulty: 24 easy, 10 medium, 1 hard.
| Classification of milk proteins and nitrogen fractions | 5 | |
| Caseins: alpha-s1, alpha-s2, beta and kappa | 4 | |
| Immunoglobulins, lactoferrin, lysozyme and lactoperoxidase | 4 | |
| Casein micelle structure and models | 3 | |
| Micelle stability: calcium phosphate, kappa-casein and zeta potential | 3 | |
| Genetic polymorphism of milk proteins, including A1 and A2 beta-casein | 3 | |
| Heat denaturation of whey proteins and whey protein-casein interactions | 3 | |
| Whey proteins: beta-lactoglobulin and alpha-lactalbumin | 2 | |
| Milk fat globule membrane proteins | 2 | |
| Enzyme indicators of heat treatment | 2 | |
| Bioactive peptides and protein hydrolysates | 2 | |
| Indigenous enzymes: alkaline phosphatase, lactoperoxidase, lipoprotein lipase, plasmin | 1 | |
| Milk protein allergenicity | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A milk has total N 0.50 per cent, non-casein N 0.11 per cent and non-protein N 0.028 per cent. What is its casein content (factor 6.38)?
B. 2.49 per cent
Casein = (TN - NCN) x 6.38 = 0.39 x 6.38 = 2.49%. 3.19 is crude protein (TN x 6.38); 0.70 is NCN x 6.38; 3.01 is true protein (TN - NPN) x 6.38.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 1: Proteins
Which casein contains no cysteine and has five phosphate groups clustered near its N-terminus?
C. Beta-casein
Beta-casein has 5 phosphoserines in its N-terminal region and no cysteine. Kappa- and alpha-s2-casein each have two cysteines; alpha-s1 has no cysteine but 8-9 phosphates.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which is the only major casein that is glycosylated?
A. Kappa-casein
Kappa-casein carries oligosaccharide chains with galactose, N-acetylgalactosamine and sialic acid in its C-terminal region.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
How many amino acid residues does the caseinomacropeptide released by chymosin contain?
C. 64
CMP is residues 106-169 of kappa-casein, i.e. 169 - 105 = 64 residues. 105 is para-kappa-casein; 169 is the whole molecule.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
The protruding 'hairy layer' on the surface of casein micelles is formed mainly by:
A. The C-terminal segments of kappa-casein
The hydrophilic, negatively charged caseinomacropeptide region of kappa-casein forms the brush that provides steric stabilisation.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which peptide is released more readily from A1 than from A2 beta-casein during digestion?
D. Beta-casomorphin-7
BCM-7 (beta-casein 60-66) is released when the bond before His67 is cleaved, which proline at 67 in A2 hinders. CMP comes from kappa-casein; lactoferricin from lactoferrin.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 1: Proteins
The main immunoglobulin class in bovine milk and colostrum is:
D. IgG1
Bovine colostrum and milk are dominated by IgG1 transferred from blood; human milk by secretory IgA.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 1: Proteins
Lactoferrin inhibits bacteria mainly by:
A. Binding iron so that bacteria cannot use it
Iron sequestration is bacteriostatic; pepsin also releases antimicrobial lactoferricin. The thiocyanate reaction is the lactoperoxidase system; cell wall hydrolysis is lysozyme.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which protein is the most abundant protein of the bovine milk fat globule membrane?
A. Butyrophilin
Butyrophilin is the major MFGM protein in cow milk. Beta-lactoglobulin is a whey protein; kappa-casein is in micelles.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
A negative alkaline phosphatase test on bottled milk indicates that:
B. The milk was adequately pasteurised and not contaminated with raw milk afterwards
ALP destruction shows at least minimum pasteurisation; it says nothing about spores, and a positive peroxidase result would show heating did not reach about 80 C.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 1: Proteins
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