ICAR AIEEA-PG Dairy Colloids: Emulsions, Foams & Gels: practice questions

1 · Emulsifiers and the HLB concept · easy

What is the approximate HLB of distilled monoglycerides?

1. About 3–4
2. About 10–12
3. About 15
4. About 18–20

2 · Emulsion formation, homogenisation and stability · medium

What is the purpose of the second stage of a two-stage homogeniser?

1. To separate the cream from the skim milk after the first stage
2. To raise the fat globule size back to about 4 µm for flavour
3. To pasteurise the milk by the heat generated in the valve
4. To break up clusters of newly formed globules sharing casein

3 · Emulsion formation, homogenisation and stability · medium

What mainly covers the new fat surface created by homogenising milk?

1. Fresh milk fat globule membrane synthesised by enzymes during homogenisation
2. Adsorbed casein micelles and fragments, plus whey protein
3. Lactose crystals that deposit from the serum onto every globule surface
4. Nothing; the new surface stays bare until the milk is pasteurised

4 · Emulsion formation, homogenisation and stability · medium

Why must raw milk not be homogenised and then held before heat treatment?

1. Homogenised raw milk coagulates within minutes because of the pressure
2. The new globules rise faster and form a solid cream plug
3. Homogenisation raises the bacterial count tenfold in raw milk
4. Disrupted membranes let milk lipase act quickly, causing rancidity

5 · Foams: formation, structure and stability; whipped cream and overrun · easy

Why is cream whipped cold, at about 5 °C?

1. So the fat is partly crystalline and partially coalesces
2. So that all the fat is fully liquid and spreads over the bubbles
3. So that bacteria cannot grow during the minute of whipping
4. So that the cream freezes and holds its shape immediately

6 · Protein and polysaccharide gels · easy

With which cation does κ-carrageenan form firm, brittle gels?

1. Magnesium only
2. Potassium
3. Sodium only
4. Calcium only, in the form of the egg-box

7 · Protein and polysaccharide gels · medium

Fat globules bound to a protein gel network, increasing its firmness, are called:

1. Inactive fillers
2. Active fillers
3. Depletants
4. Antifoams

8 · Hydrocolloid stabilisers and protein-polysaccharide interactions · medium

How does high-methoxyl pectin stabilise acidified milk drinks at pH about 4?

1. It hydrolyses casein into soluble peptides
2. It raises the pH back to 6.7 so that casein is negatively charged again
3. It adsorbs on positive casein and repels by steric and charge effects
4. It forms a calcium egg-box gel that traps every particle

9 · Organogels, hydrogels and nanoemulsions · easy

Nanoemulsions are commonly defined as emulsions with mean droplet radius below about:

1. 10 µm
2. 1 nm
3. 1 mm
4. 100 nm

10 · Organogels, hydrogels and nanoemulsions · easy

Which device makes nanoemulsions by colliding two high-velocity jets in an interaction chamber?

1. Colloid mill
2. Microfluidiser
3. Paddle mixer
4. Cream separator