ICAR AICE-JRF/SRF Food Chemistry I: Water, Carbohydrates, Proteins & Lipids: practice questions

1 · Water in foods: structure, bound and free water, sorption isotherms and water activity · hard

On the food stability map, lipid oxidation in a dried food is slowest at

1. the very lowest water activity, as close to aw 0 as possible
2. an intermediate water activity of about aw 0.7–0.8
3. about the monolayer water activity, roughly aw 0.2–0.3
4. the highest water activity, just below aw 1.0

2 · Glass transition and molecular mobility · hard

Using the Gordon–Taylor equation with Tg(sucrose) = 62 °C, Tg(water) = −135 °C and k = 4.7, the Tg of amorphous sucrose containing 5 % water is closest to

1. 52 °C
2. 23 °C
3. 60 °C
4. 27 °C

3 · Glass transition and molecular mobility · medium

Tg′ in frozen foods refers to the glass transition of

1. pure ice at atmospheric pressure
2. the food before any freezing begins
3. the packaging film around the food
4. the maximally freeze-concentrated unfrozen phase

4 · Starch: structure, gelatinisation, pasting and retrogradation · hard

A frozen sauce shows weeping and a spongy texture after freeze–thaw cycles. Which starch would best correct this?

1. An acid-thinned starch
2. A hydroxypropylated or acetylated starch
3. A native potato starch
4. A pregelatinised normal maize starch

5 · Cellulose, pectic substances, gums and dietary fibre · hard

Oat and barley β-glucans are associated with lowering blood cholesterol mainly because they

1. are digested to glucose that inhibits cholesterol synthesis in the liver
2. form viscous solutions in the gut that slow absorption and bind bile acids
3. contain plant sterols that replace cholesterol in cell membranes
4. are insoluble fibres that only increase faecal bulk

6 · Amino acids, peptides and protein structure · hard

Melamine was added to some protein ingredients as an adulterant because

1. Kjeldahl and Dumas methods measure total nitrogen, so nitrogen-rich melamine inflates apparent protein
2. melamine binds to proteins and makes them more soluble in standard extraction tests
3. melamine is an essential amino acid that raises the true protein quality
4. melamine reacts with protein to form extra peptide bonds detected by titration

7 · Protein denaturation and functional properties: solubility, gelation, emulsification and foaming · medium

Egg white fails to whip into a stable foam in a bowl containing traces of fat because

1. lipids compete for the air–water interface and disrupt the protein film
2. fat raises the pH so that the proteins become fully denatured at once
3. fat binds the water and leaves no liquid to form the foam lamellae
4. fat makes the egg-white proteins far too stable to unfold at the bubble surface

8 · Post-mortem changes and tenderisation of muscle proteins · easy

Papain, bromelain and ficin, used as meat tenderisers, are obtained respectively from

1. papaya, pineapple and fig
2. pineapple, fig and papaya
3. fig, papaya and pineapple
4. papaya, fig and pineapple

9 · Lipid oxidation: autoxidation, photo-oxidation, rancidity and antioxidants · easy

An oil has a peroxide value of 4 meq/kg and a p-anisidine value of 6. Its totox value is

1. 10
2. 16
3. 14
4. 24

10 · Chemical and physical changes in macronutrients during processing · medium

Caramelisation differs from the Maillard reaction in that caramelisation

1. involves sugars alone heated to high temperature, without amino compounds
2. requires amino acids and reducing sugars at moderate temperature
3. occurs only in proteins and never in carbohydrates or sugar syrups heated alone
4. takes place at refrigeration temperatures over long storage