ASRB NET and ARS: dairy disciplines · India · Agricultural Scientists Recruitment Board (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)
ASRB NET and ARS — Dairy Chemistry
Master's-level recall of product compositions and standards, ghee constants and methods, flavour compounds of fermented products, ripening agents and indices, and stabilisers and emulsifiers in ice cream.
How our questions for ASRB NET and ARS spread across the units of Chemistry of Dairy Products. Difficulty: 17 easy, 13 medium, 1 hard.
| Heat stability of milk and the heat coagulation time | 3 | |
| Age gelation of UHT milk | 3 | |
| Chemistry of cream: neutralisation and ripening | 3 | |
| Mechanism of churning and butter microstructure | 3 | |
| Chemistry of rennet coagulation | 3 | |
| Changes during cheese ripening: glycolysis, proteolysis, lipolysis | 3 | |
| Chemistry of milk fermentation and flavour compounds | 3 | |
| Ghee: composition by method, analytical constants, flavour and deterioration | 2 | |
| Concentrated milks: physico-chemical changes in manufacture and storage | 2 | |
| Milk powders: structure, solubility and instant properties | 2 | |
| Ice cream: structure and role of stabilisers and emulsifiers | 2 | |
| Heat-desiccated and acid-coagulated products: khoa, chhana, paneer | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
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
Why is sour cream partly neutralised before pasteurisation for butter or ghee?
B. To prevent curdling on heating and reduce fat loss
Acid cream curdles on heating, trapping fat, and salted butter from very acid cream develops off-flavours.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Cream with 40 per cent fat has a titratable acidity of 0.30 per cent. What is its serum acidity?
C. 0.50 per cent
Serum acidity = 0.30 x 100/(100 - 40) = 0.50%. 0.12 multiplies by 0.4 (the fat fraction); 0.75 divides by 0.4.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Which organisms in a butter culture produce diacetyl from citrate?
C. Lactococcus lactis biovar diacetylactis and Leuconostoc species
Citrate-fermenting mesophilic aroma bacteria make diacetyl; the yoghurt pair produce acetaldehyde.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
Cream containing 40 kilograms of fat yields 48.8 kilograms of butter. What is the overrun?
A. 22 per cent
Overrun = (48.8 - 40)/40 x 100 = 22%. 18 divides by the butter weight; 8.8 is the weight difference in kg.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
In the pre-stratification method of ghee making, butter is first held at about:
D. 80 degrees Celsius
At about 80 C, melted butter separates and the lower serum layer is drained before final clarification.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Milk with 12.5 per cent total solids is concentrated to 25 per cent total solids. What is the concentration factor?
A. 2.0
CF = 25/12.5 = 2.0; 0.5 inverts the ratio.
Further reading: Walstra, Wouters and Geurts, Dairy Science and Technology
What are vacuoles in spray-dried powder particles?
C. Air pockets formed during atomisation and droplet expansion
Vacuoles lower particle density and influence bulk density.
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
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
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