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ICAR AICE-JRF/SRF Microbiology of Dairy Products: practice questions

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 papers
10worked here, free
84written to this exam in this subject
11syllabus units

What this subject covers

The microflora, spoilage and safety of each dairy product family, from cream to ice cream to traditional products.

In the exams: ICAR AICE subject 36 Units 3 and 5; ICAR AIEEA-PG group 16 (microbiological quality of cream, butter, ice cream, concentrated and dried milks, infant foods and indigenous products)

What ICAR AICE-JRF/SRF asks from it

ICAR AICE-JRF/SRF (PhD) — Dairy Microbiology (subject 36, Units 3 and 5)

Microbiological quality of processed dairy products: flora and spoilage of cream, butter, concentrated and dried milks, infant foods, ice cream, cheeses and fermented milks, late blowing and its control, yeast and mould spoilage, and microbiological standards and sampling plans.

Where the 84 questions fall

How our questions for ICAR AICE-JRF/SRF spread across the units of Microbiology of Dairy Products. Difficulty: 19 easy, 38 medium, 27 hard.

Microbiology of concentrated and dried milks9
Microbiology of fermented milks: dahi, yoghurt, kefir, koumiss9
Microbiology of ripened cheeses and ripening flora8
Late blowing and other cheese defects8
Yeast and mould spoilage8
Microbiological standards for dairy products8
Microbiology of cream and butter7
Microbiology of infant milk foods7
Microbiology of ice cream and frozen desserts7
Microbiology of fresh cheeses7
Microbiology of traditional and heat-desiccated products6

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Microbiology of concentrated and dried milks · medium

Why do milk powders not support microbial growth?

  1. They contain added preservatives
  2. They are sterilised by spray drying
  3. They have a pH below 4
  4. Their aw is too low
Answer and working

D. Their aw is too low

Low water activity prevents growth; spores and some vegetative cells survive.

Further reading: Fox et al., Fundamentals of Cheese Science

2 · Microbiology of ripened cheeses and ripening flora · medium

A cheese has 1.8 per cent salt and 38 per cent moisture. What is its salt in moisture?

  1. About 4.7 per cent
  2. About 4.5 per cent
  3. About 21 per cent
  4. About 1.8 per cent
Answer and working

B. About 4.5 per cent

1.8/(1.8 + 38) x 100 = 4.5%. 4.7 divides by moisture only.

Further reading: Fox et al., Fundamentals of Cheese Science

3 · Late blowing and other cheese defects · medium

What is the main source of Clostridium tyrobutyricum spores in cheese milk?

  1. Rennet
  2. Salt
  3. Rinse water
  4. Silage
Answer and working

D. Silage

Spores pass from silage through faeces to teats.

Further reading: Fox et al., Fundamentals of Cheese Science

4 · Late blowing and other cheese defects · hard

Slits in Cheddar ripened at elevated temperatures are usually caused by:

  1. Heterofermentative NSLAB producing CO2
  2. Moulds producing gas
  3. Propionibacteria producing CO2
  4. Clostridium tyrobutyricum producing H2
Answer and working

A. Heterofermentative NSLAB producing CO2

Gas-forming heterofermentative lactobacilli open the texture.

Further reading: Robinson (ed.), Dairy Microbiology Handbook

5 · Late blowing and other cheese defects · hard

About how many C. tyrobutyricum spores per litre of milk can be enough to cause late blowing?

  1. One billion
  2. None; spores never cause blowing
  3. A few hundred
  4. Ten million
Answer and working

C. A few hundred

Very low spore numbers can cause the defect in susceptible cheeses.

Further reading: Robinson (ed.), Dairy Microbiology Handbook

6 · Microbiology of fermented milks: dahi, yoghurt, kefir, koumiss · medium

A yoghurt sample gives 56 colonies on a plate from 0.1 millilitre of a 1 in a million dilution. What is the count?

  1. 5.6 x 10^7 cfu per gram
  2. 5.6 x 10^6 cfu per gram
  3. 5.6 x 10^9 cfu per gram
  4. 5.6 x 10^8 cfu per gram
Answer and working

D. 5.6 x 10^8 cfu per gram

56 / (0.1 x 10^-6) = 5.6 x 10^8. 5.6 x 10^7 forgets the 0.1 mL.

Further reading: Fox et al., Fundamentals of Cheese Science

7 · Microbiology of traditional and heat-desiccated products · medium

Kulfi made without effective pasteurisation after mixing carries risks similar to:

  1. Butter oil
  2. Ice cream
  3. Ghee
  4. Milk powder
Answer and working

B. Ice cream

It is a frozen dairy dessert with similar contamination routes.

Further reading: Fox et al., Fundamentals of Cheese Science

8 · Microbiology of traditional and heat-desiccated products · easy

Rasogolla keeps reasonably well mainly because it is:

  1. Salted heavily
  2. Dried to 5 per cent moisture
  3. Stored in sugar syrup
  4. Fermented with yeasts
Answer and working

C. Stored in sugar syrup

The syrup lowers water activity; canning extends shelf life.

Further reading: Robinson (ed.), Dairy Microbiology Handbook

9 · Microbiological standards for dairy products · medium

If 2 per cent of units in a lot are contaminated and five samples are tested with c = 0, about how often is the lot accepted?

  1. About 98 per cent
  2. About 90 per cent
  3. About 10 per cent
  4. About 50 per cent
Answer and working

B. About 90 per cent

(1 - 0.02)^5 = 0.904, so the lot is accepted about 90 per cent of the time despite contamination.

Further reading: Fox et al., Fundamentals of Cheese Science

10 · Microbiological standards for dairy products · hard

With 2 per cent of units contaminated and c = 0, about how often is the lot accepted if 60 samples are tested?

  1. About 90 per cent
  2. About 2 per cent
  3. About 30 per cent
  4. About 60 per cent
Answer and working

C. About 30 per cent

(0.98)^60 = 0.298; more samples give better detection.

Further reading: Robinson (ed.), Dairy Microbiology Handbook

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Read the subject

Microbiology of Dairy ProductsThe full study manual, free ICAR AICE-JRF/SRFFormat, sections and how it has changed

More ICAR AICE-JRF/SRF practice

Rheology & Texture of Dairy FoodsFermentation Technology & Dairy BiotechnologyInstrumentation, Process Control & AutomationAdvanced Dairy MicrobiologyAdvanced Dairy Technology & Product DevelopmentAdvanced Dairy EngineeringResearch Methods, Experimental Design & Scientific CommunicationAdvanced Dairy ChemistryStarter Cultures & Lactic Acid BacteriaDairy Pathogens, Toxins & Microbial RiskQuality Assurance, Statistical Quality Control & Laboratory ManagementDairy Analysis & Instrumental MethodsMicrobiology of Raw & Market MilkChemistry of Dairy ProductsMilk Proteins & EnzymesMembrane Processing & Dairy IngredientsLactose, Milk Salts & VitaminsProbiotics, Prebiotics & Functional Dairy FoodsMicrobiological Quality Assurance & Rapid MethodsDairy Effluent Treatment & Environmental ManagementMilk LipidsEmerging & Non-thermal Dairy ProcessingDairy Plant Utilities & Energy ManagementFermented Milks Technology

Microbiology of Dairy Products for other exams

ICAR AIEEA-PG · IndiaASRB NET and ARS · India

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