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 papersThe lactic acid bacteria and other organisms used as starters: their metabolism, genetics, production, failure and control.
In the exams: ICAR AICE subject 36 Unit 5; ICAR AIEEA-PG group 16 (classification, genetic aspects and carbohydrate metabolism of LAB; propagation and inhibition of starters)
ICAR AICE-JRF/SRF (PhD) — Dairy Microbiology (subject 36, Unit 5)
Starter cultures and LAB: taxonomy, carbohydrate, citrate and protein metabolism, mesophilic and thermophilic starters, culture types, propagation and preservation, bacteriophage biology and control, inhibitors and bacteriocins, plasmid biology and strain improvement.
How our questions for ICAR AICE-JRF/SRF spread across the units of Starter Cultures & Lactic Acid Bacteria. Difficulty: 20 easy, 49 medium, 29 hard.
| Bacteriophage in dairy plants and its control | 12 | |
| Lactose, galactose and citrate metabolism; diacetyl formation | 9 | |
| Homofermentative and heterofermentative metabolism | 8 | |
| Proteolytic systems of starters | 8 | |
| Mesophilic and thermophilic starters | 8 | |
| Adjunct and secondary cultures: propionibacteria, moulds, smear bacteria | 8 | |
| Starter propagation, bulk starter systems and direct-vat-set cultures | 8 | |
| Inhibition by antibiotics, sanitisers and bacteriocins | 8 | |
| Genetics and genetic improvement of starters | 8 | |
| Lactic acid bacteria: genera and current taxonomy | 7 | |
| Single, multiple and mixed-strain starters; defined and undefined cultures | 7 | |
| Preservation of cultures: freezing and freeze-drying | 7 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
From one molecule of glucose, a heterofermentative LAB produces:
D. Lactate, CO2 and ethanol or acetate
One lactate, one CO2 and one ethanol (or acetate).
Further reading: Fox et al., Fundamentals of Cheese Science
Why does yoghurt contain free galactose?
A. Galactose is excreted
Galactose-negative S. thermophilus and L. bulgaricus export galactose via LacS.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
Which organism ferments citrate to produce diacetyl?
C. Lactococcus lactis biovar diacetylactis
Biovar diacetylactis has the citrate permease CitP; Leuconostoc also uses citrate.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
Leuconostoc species metabolise citrate mainly when:
C. Lactose is also available and the pH has fallen
Citrate co-metabolism by Leuconostoc is favoured at acid pH with sugar present.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
Natural whey cultures are the traditional starters for:
D. Parmigiano Reggiano and Grana Padano
Whey from the previous day's make is incubated to select thermophilic LAB.
Further reading: Fox et al., Fundamentals of Cheese Science
Multiple-strain defined starters usually contain:
A. Two to six selected strains
A few characterised strains provide back-up if one is attacked.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
Which smear organism gives the orange colour of washed-rind cheeses?
B. Brevibacterium linens and related species
Brevibacteria produce carotenoid pigments.
Further reading: Fox et al., Fundamentals of Cheese Science
Why are frozen culture pellets added directly to milk instead of being thawed slowly first?
C. Slow thawing harms viability
Rapid thawing in milk limits damage and avoids contamination.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
45 plaques form from 0.1 millilitre of a 1 in a million dilution of whey. What is the phage titre?
D. 4.5 x 10^8 pfu per millilitre
45 / (0.1 x 10^-6) = 4.5 x 10^8 pfu/mL. 4.5 x 10^7 forgets the 0.1 mL volume.
Further reading: Fox et al., Fundamentals of Cheese Science
Bacteriocins are distinguished from many other inhibitors because they are:
C. Inactivated by proteases
They are peptides, so proteases destroy them.
Further reading: Cogan and Accolas (eds), Dairy Starter Cultures
Ten here, 98 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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