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ICAR AICE-JRF/SRF Food Structure, Colloids, Encapsulation & Nanotechnology: practice questions

ICAR AICE-JRF/SRF (PhD) — Food Processing Technology, Food Safety & Quality, Processing and Food Engineering · India · ICAR through the National Testing Agency

Original practice questions written to the published syllabus · not past papers
10worked here, free
83written to this exam in this subject
12syllabus units

What this subject covers

How the arrangement of molecules and phases decides texture, stability and digestion: emulsions, foams, gels and their stability, structure-function design, encapsulation and delivery of bioactives, digestion models, and the science and regulation of nanoscale food materials.

In the exams: ICAR AIEEA-PG Code 18 Unit I (colloidal systems, gels and emulsions); ICAR AICE 35.b Unit 5 (emulsions, foams, gels; hydrocolloids)

Where the 83 questions fall

How our questions for ICAR AICE-JRF/SRF spread across the units of Food Structure, Colloids, Encapsulation & Nanotechnology. Difficulty: 11 easy, 60 medium, 12 hard.

Nanoemulsions, liposomes and nanoparticles9
Safety assessment and regulation of nanomaterials in food9
Emulsion formation and stability mechanisms8
Protein-polysaccharide interactions8
In-vitro digestion models and bioaccessibility8
Nanotechnology in packaging and sensing8
Interfacial science: surfactants and proteins at interfaces7
Colloidal systems in foods: dispersions, emulsions, foams and gels6
Structure-function relationships and food structure design6
Microencapsulation: spray drying, coacervation and extrusion6
Foams and aerated foods4
Protein and polysaccharide gels4

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 · Colloidal systems in foods: dispersions, emulsions, foams and gels · medium

Which average droplet diameter is most sensitive to a few large droplets formed by coalescence?

  1. Number mean diameter
  2. Modal number diameter
  3. d₄₃ (volume-weighted mean)
  4. d₃₂ (surface-weighted mean)
Answer and working

C. d₄₃ (volume-weighted mean)

d₄₃ = Σnd⁴/Σnd³ weights large droplets heavily; d₃₂ relates to surface area.

Further reading: McClements, Food Emulsions; Dickinson, An Introduction to Food Colloids

2 · Emulsion formation and stability mechanisms · medium

Why is two-stage homogenisation used for cream and milk products?

  1. The second stage whips air into the emulsion
  2. The second stage pasteurises the product completely
  3. The second stage removes the emulsifier from droplets
  4. It breaks up droplet clusters
Answer and working

D. It breaks up droplet clusters

A lower-pressure second stage disperses clusters formed after the first stage.

Further reading: McClements, Food Emulsions; Dickinson, An Introduction to Food Colloids

3 · Protein-polysaccharide interactions · medium

Why is high-methoxyl pectin added to drinking yoghurt at pH about 4?

  1. It makes the whole drink set into a firm gel
  2. It raises the pH of the drink above 7
  3. It coats casein and stops aggregation
  4. It removes the lactose from the drink
Answer and working

C. It coats casein and stops aggregation

Adsorbed pectin gives negative charge and steric repulsion to casein near its pI.

Further reading: Phillips and Williams, Handbook of Hydrocolloids; Walstra, Physical Chemistry of Foods

4 · Protein-polysaccharide interactions · medium

Why is gum arabic an excellent emulsifier for beverage emulsions?

  1. It is a pure protein containing no carbohydrate at all
  2. It raises the interfacial tension of the oil sharply
  3. Protein anchors it; the carbohydrate gives steric repulsion
  4. It forms a firm gel with the calcium in the water
Answer and working

C. Protein anchors it; the carbohydrate gives steric repulsion

The protein-arabinogalactan complex adsorbs and provides a thick steric layer stable to acid and salt.

Further reading: Phillips and Williams, Handbook of Hydrocolloids; Walstra, Physical Chemistry of Foods

5 · Microencapsulation: spray drying, coacervation and extrusion · easy

A spray-dried fish oil powder has 30 g total oil and 1.5 g surface oil per 100 g. What is the encapsulation efficiency?

  1. 105%
  2. 95%
  3. 5%
  4. 28.5%
Answer and working

B. 95%

EE = (30 − 1.5)/30 × 100 = 95%. 5% is the surface fraction; 28.5% is the encapsulated mass in g; 105% adds the values.

Further reading: Zuidam and Nedović, Encapsulation Technologies; McClements, Food Emulsions

6 · Microencapsulation: spray drying, coacervation and extrusion · medium

What is a key advantage of complex coacervation over spray drying for fish oil?

  1. Much higher payloads
  2. No wall materials are needed at all
  3. Lower cost than any other encapsulation method
  4. It works without any water in the process
Answer and working

A. Much higher payloads

Coacervates can hold well above 50% oil.

Further reading: Zuidam and Nedović, Encapsulation Technologies; McClements, Food Emulsions

7 · Microencapsulation: spray drying, coacervation and extrusion · medium

Which wall material forms inclusion complexes holding small flavour molecules in a cavity?

  1. Gum arabic
  2. β-Cyclodextrin
  3. Sodium caseinate
  4. Maltodextrin of low DE
Answer and working

B. β-Cyclodextrin

Cyclodextrins have hydrophobic cavities that host small non-polar molecules.

Further reading: Zuidam and Nedović, Encapsulation Technologies; McClements, Food Emulsions

8 · Microencapsulation: spray drying, coacervation and extrusion · medium

What is spray chilling?

  1. Drying a solution of the wall material in hot air
  2. Freezing a gel of the active in liquid nitrogen
  3. Atomising molten fat with the active into cold air
  4. Coating particles with a polymer in a hot fluid bed
Answer and working

C. Atomising molten fat with the active into cold air

Droplets solidify as lipid matrices that release on melting.

Further reading: Zuidam and Nedović, Encapsulation Technologies; McClements, Food Emulsions

9 · Nanoemulsions, liposomes and nanoparticles · medium

How are chitosan nanoparticles formed by ionic gelation?

  1. Chitosan is cross-linked by tripolyphosphate
  2. Chitosan is precipitated by adding ethanol
  3. Chitosan is melted and extruded into strands
  4. Chitosan is hydrolysed completely to glucosamine
Answer and working

A. Chitosan is cross-linked by tripolyphosphate

Electrostatic cross-linking between protonated amines and TPP forms particles.

Further reading: Zuidam and Nedović, Encapsulation Technologies; McClements, Food Emulsions

10 · In-vitro digestion models and bioaccessibility · hard

Why should in-vitro digestion results on a functional ingredient be followed by human studies before health claims?

  1. They omit absorption, regulation and microbiota
  2. Human studies are cheaper than in-vitro tests
  3. Regulators accept only animal studies for claims
  4. In-vitro models always overestimate digestion tenfold
Answer and working

A. They omit absorption, regulation and microbiota

Models compare products and mechanisms but cannot capture whole-body physiology.

Further reading: Brodkorb et al. (2019) INFOGEST protocol

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Read the subject

Food Structure, Colloids, Encapsulation & NanotechnologyThe full study manual, free ICAR AICE-JRF/SRFFormat, sections and how it has changed

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