ICAR AICE-JRF/SRF (PhD): Dairy Chemistry, Dairy Microbiology, Dairy Technology, Dairy Engineering · India · NTA for ICAR
Original practice questions written to the published syllabus · not past papersWhat milk is made of, how composition varies, and the physical properties used to test and process it.
In the exams: ICAR AICE subject 34 Unit 1; ICAR AIEEA-PG group 16 (composition and physico-chemical properties of milk and colostrum); ASRB NET Dairy Chemistry
ICAR AICE-JRF/SRF (PhD) — Dairy Chemistry (subject 34, Unit 1)
Milk constituents and their distribution between phases, species differences, colostrum, and the physical properties of milk with their causes: freezing point and its constancy, buffering and the role of colloidal calcium phosphate, redox potential, viscosity and surface tension. Expect reasoning questions on why a property changes in mastitic, late-lactation, watered or soured milk.
How our questions for ICAR AICE-JRF/SRF spread across the units of Milk Composition & Physical Properties. Difficulty: 7 easy, 26 medium, 17 hard.
| Species differences: cow, buffalo, goat, sheep, camel, human | 6 | |
| Gross composition of milk and its normal ranges | 5 | |
| Variation with breed, feed, season, lactation stage and mastitis | 5 | |
| Buffer capacity and acid-base equilibria | 5 | |
| Viscosity, surface tension and interfacial tension | 5 | |
| Electrical conductivity, refractive index and thermal properties | 5 | |
| Acidity and pH; titratable acidity | 4 | |
| Oxidation-reduction potential | 4 | |
| Colour and optical properties of milk | 4 | |
| Colostrum and abnormal milks | 3 | |
| Density and specific gravity; lactometer readings | 2 | |
| Freezing point and its use in detecting added water | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In typical cow milk, casein makes up roughly what share of total protein?
C. About 80 per cent
Casein is about 80% of cow milk protein (about 2.6% of milk) and whey proteins about 20%. 20% is the whey share; 50% is closer to human milk, which is whey-dominant.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
What is the typical size range of casein micelles in cow milk?
B. About 50 to 500 nanometres, averaging near 150 to 200 nanometres
Micelles are colloidal, about 50-500 nm (mean about 150-200 nm). The 0.1-15 um range is the fat globules; 3-6 nm is individual whey protein molecules.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which protein is absent from both human and camel milk but is the main whey protein of cow milk?
D. Beta-lactoglobulin
Beta-lactoglobulin is absent from human and camel milk. Alpha-lactalbumin is present in all, as the lactose synthase subunit. Lactoferrin is higher in human milk.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
At which stage of lactation are the fat and protein contents of cow milk usually lowest?
A. Around peak yield, roughly the second month
After colostrum, fat and protein fall to their lowest near peak yield (about month 2), then rise as yield declines, so late-lactation milk is richer. The first days after calving give colostrum, the richest secretion.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
A farm uses a hydrometer-type colostrometer to check colostrum. What property does it actually measure?
C. Specific gravity, which rises with immunoglobulin and total solids content
A colostrometer is a hydrometer reading specific gravity, which correlates with immunoglobulin content. A Brix refractometer, the other farm tool, reads refractive index, which rises (not falls) with solids.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Which milk component contributes most to the viscosity of whole milk?
C. Casein micelles
Casein micelles, by volume fraction, contribute most, followed by fat globules; whey proteins and lactose contribute less.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
The specific heat of whole milk is about:
B. 3.9 kilojoules per kilogram per kelvin
Whole milk is about 3.9 kJ/kg K, slightly below water (4.18) because solids, especially fat, have lower specific heat.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
In a clean-in-place system, conductivity probes are mainly used to:
D. Distinguish product, rinse water and detergent and control changeover
Water, milk, caustic and acid differ widely in conductivity, so probes control phase changeover and detergent strength.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Why is a low redox potential important inside a ripening cheese?
D. It favours the anaerobic and facultative organisms and reactions of ripening
Cheese interiors have a negative Eh, which suits facultative and anaerobic starter and non-starter bacteria and influences flavour chemistry; it does not stop microbial growth.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Camel milk is notably richer than cow milk in which vitamin?
D. Vitamin C
Camel milk contains several times more vitamin C than cow milk, important in arid diets.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Ten here, 50 in the app. The Laisha app has every practice question we have written to ICAR AICE-JRF/SRF in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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