ASRB NET and ARS: dairy disciplines · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersLactose chemistry and crystallisation, the salt system of milk, trace elements and water-soluble vitamins.
In the exams: ICAR AICE subject 34 Unit 1; ICAR AIEEA-PG group 16 (lactose crystallisation and its significance)
ASRB NET and ARS — Dairy Chemistry
Recall at Master's depth: alpha and beta lactose properties, the 93.5 degree transition, sucrose ratio, salt concentrations and partition, stabilising salts, trace elements, vitamin contents and stabilities.
How our questions for ASRB NET and ARS spread across the units of Lactose, Milk Salts & Vitamins. Difficulty: 20 easy, 5 medium, 4 hard.
| Lactose structure, alpha and beta forms and mutarotation | 5 | |
| Lactose solubility and crystallisation | 4 | |
| Maillard browning and its control | 4 | |
| Lactose biosynthesis and intolerance | 3 | |
| Milk salts: calcium, phosphate, citrate and their partition | 3 | |
| Lactose in sweetened condensed milk, powders and ice cream | 2 | |
| Lactose derivatives: lactulose, galacto-oligosaccharides, lactitol, lactobionic acid | 2 | |
| Salt balance and heat stability | 2 | |
| Trace elements in milk | 2 | |
| Water-soluble vitamins and their losses in processing | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Compared with sucrose, the sweetness of lactose is roughly:
D. One fifth to one third
Lactose has low relative sweetness, so milk does not taste sweet despite about 4.7% lactose.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 3: Lactose, Water, Salts and Minor Constituents
Below about which temperature does lactose crystallise from solution as alpha-lactose monohydrate?
B. 93.5 degrees Celsius
Below about 93.5 C alpha-monohydrate crystallises; above it, anhydrous beta-lactose.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 3: Lactose, Water, Salts and Minor Constituents
Why is sweetened condensed milk seeded with finely ground lactose during rapid cooling?
A. To provide many nuclei so that lactose crystallises as many small crystals
Lactose is supersaturated in SCM, so crystallisation cannot be avoided; seeding at high supersaturation gives many small crystals and a smooth texture.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
The Maillard reaction in milk occurs mainly between lactose and:
A. The epsilon-amino group of lysine residues
Reducing sugars react with free amino groups, chiefly lysine's epsilon-amino group in proteins.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
At about what water activity is Maillard browning fastest?
D. 0.6 to 0.7
Browning peaks at intermediate water activity, typical of concentrated and partly dried products.
Further reading: McSweeney and Fox (eds), Advanced Dairy Chemistry Vol. 3: Lactose, Water, Salts and Minor Constituents
Lactose synthase consists of:
A. Beta-1,4-galactosyltransferase and alpha-lactalbumin
Alpha-lactalbumin changes galactosyltransferase specificity so glucose becomes the acceptor.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Lactose intolerance is caused by:
A. Low intestinal lactase activity, leaving lactose undigested
It is a non-immune malabsorption; galactose metabolism defects cause galactosaemia.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which ions in milk are almost entirely in the soluble phase?
C. Sodium, potassium and chloride
Monovalent ions do not bind the micelles; calcium, magnesium and phosphate are partly colloidal.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
In the salt balance theory, which ions tend to destabilise milk on heating?
A. Calcium and magnesium
Divalent cations reduce casein charge and bridge micelles; phosphate and citrate bind them and stabilise.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Which trace element in milk is technologically important mainly as a catalyst of lipid oxidation?
C. Copper
Copper, even at fractions of a mg/L, catalyses oxidation; this is why copper fittings were replaced by stainless steel.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Ten here, 29 in the app. The Laisha app has every practice question we have written to ASRB NET and ARS 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.
Free for ten days, then one subscription of US$10 a month. We would rather say so here than have you find it later.
An AI operating system for agriculture: free guides, manuals and tools written for every country.