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 papersPhysical and chemical changes in milk as it becomes cream, butter, ghee, concentrated and dried milks, cheese, fermented milks and frozen desserts.
In the exams: ICAR AICE subject 34 Units 5–8; ICAR AIEEA-PG group 16 (chemistry of cream, butter, ghee, ice cream, cheese, condensed and dried milks, infant food)
ICAR AICE-JRF/SRF (PhD) — Dairy Chemistry (subject 34, Units 5-8)
Chemistry of cream, butter and ghee; heat stability, concentrated and dried milks, khoa, chhana and paneer; chemistry of cheese and fermented milks; ice cream. Questions test mechanisms such as churning, age gelation, rennet coagulation, ripening reactions, diacetyl formation and emulsifier action, and their links to defects.
How our questions for ICAR AICE-JRF/SRF spread across the units of Chemistry of Dairy Products. Difficulty: 14 easy, 48 medium, 25 hard.
| Changes during cheese ripening: glycolysis, proteolysis, lipolysis | 9 | |
| Chemistry of cream: neutralisation and ripening | 8 | |
| Milk powders: structure, solubility and instant properties | 8 | |
| Chemistry of rennet coagulation | 8 | |
| Ice cream: structure and role of stabilisers and emulsifiers | 8 | |
| Mechanism of churning and butter microstructure | 7 | |
| Concentrated milks: physico-chemical changes in manufacture and storage | 7 | |
| Chemistry of milk fermentation and flavour compounds | 7 | |
| Heat-desiccated and acid-coagulated products: khoa, chhana, paneer | 7 | |
| Heat stability of milk and the heat coagulation time | 6 | |
| Age gelation of UHT milk | 6 | |
| Ghee: composition by method, analytical constants, flavour and deterioration | 6 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Above about pH 6.7, heating milk causes which change in kappa-casein that contributes to instability?
C. Dissociation from the micelles
Kappa-casein (with denatured beta-lactoglobulin) leaves the micelles at higher pH, leaving micelles depleted of their stabilising layer.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Which enzymes are chiefly responsible for proteolytic age gelation of UHT milk?
B. Plasmin and heat-stable proteases of psychrotrophic bacteria
Plasmin and Pseudomonas proteases survive UHT; LPL, ALP and lactoperoxidase are inactivated and are not proteases.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
What gives traditional ghee its granular texture?
A. Slow cooling
Slow cooling at moderate temperatures favours large crystal aggregates.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Using Van Slyke's formula Y = (0.93F + C - 0.1) x 1.09 / (1 - W), what is the yield of Cheddar from 100 kilograms of milk with 3.6 per cent fat, 2.5 per cent casein and 37 per cent cheese moisture?
A. About 9.9 kilograms
(3.348 + 2.5 - 0.1) x 1.09/0.63 = 9.94 kg. 6.3 omits the moisture term; 9.1 omits the 1.09 factor.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
What does a high C/P ratio of a coagulant mean?
C. High clotting activity relative to general proteolysis
A high clotting-to-proteolysis ratio gives good yield and less bitterness.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Which coagulant is now the most widely used in cheesemaking?
D. Fermentation-produced chymosin
Chymosin produced by microorganisms carrying the gene is widely used.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which coagulant is noted for very specific kappa-casein cleavage with little general proteolysis?
C. Camel chymosin
Camel chymosin has a high C/P ratio; mould proteases are more proteolytic.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Residual chymosin in cheese first hydrolyses which bond, producing alpha-s1-I-casein?
C. Phe23-Phe24 of alpha-s1-casein
Chymosin cleaves alpha-s1-casein at Phe23-Phe24 early in ripening, softening texture. Lys28-Lys29 is a plasmin site.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Which structural element of ice cream stabilises the air cells and gives melt resistance?
D. The partially coalesced fat network
Partially coalesced fat surrounds air cells.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which agent in Dutch-type cheeses produces the small round openings?
C. Citrate-fermenting lactococci and leuconostocs producing CO2
Citrate fermentation gives CO2 and diacetyl, forming small eyes.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
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