ASRB NET and ARS Milk Lipids: practice questions

1 · Lipid classes in milk: triglycerides, phospholipids, sterols · easy

Which three phospholipids are the main ones in cow milk?

1. Cerebroside, ganglioside and phosphatidylglycerol
2. Phosphatidylserine, phosphatidylinositol and cardiolipin
3. Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin
4. Lysophosphatidylcholine, ethanolamine plasmalogen and phosphatidic acid

2 · Fatty acid profile of milk fat and factors affecting it · easy

Which fatty acid is present in the largest proportion in cow milk fat?

1. Palmitic acid
2. Linoleic acid
3. Lauric acid
4. Butyric acid

3 · Biosynthesis of milk fat · medium

Which fatty acids of milk fat are synthesised entirely within the mammary gland?

1. C4 to C14 acids, plus about half of the palmitic acid
2. Only butyric acid; all others come from the blood
3. All fatty acids, because none are taken up from blood
4. C18 acids, plus about half of the palmitic acid

4 · Conjugated linoleic acid · easy

Which isomer makes up most of the conjugated linoleic acid in milk fat?

1. Trans-10, cis-12 C18:2
2. Trans-11 C18:1 (vaccenic acid)
3. Cis-9, cis-12 C18:2 (linoleic acid)
4. Cis-9, trans-11 C18:2 (rumenic acid)

5 · Milk fat globule and its membrane · easy

The milk fat globule membrane has which structure?

1. A crystalline shell of high-melting triglycerides with no proteins or phospholipids at the surface
2. A double layer of whey proteins bound by calcium phosphate
3. A single layer of adsorbed casein micelles formed after secretion
4. An inner monolayer from the endoplasmic reticulum and an outer bilayer from the plasma membrane

6 · Auto-oxidation: mechanism, factors and measurement · easy

In the propagation stage of auto-oxidation, a peroxyl radical:

1. Is formed directly from a saturated fatty acid without oxygen
2. Combines with another radical to form a stable non-radical product that ends the reaction chain
3. Reacts with an antioxidant to stop the chain
4. Removes hydrogen from another fatty acid, forming a hydroperoxide and a new lipid radical

7 · Auto-oxidation: mechanism, factors and measurement · medium

Which metal is the most active catalyst of lipid oxidation in milk?

1. Copper
2. Zinc
3. Magnesium
4. Calcium

8 · Antioxidants: natural and synthetic · easy

Citric acid improves the effect of phenolic antioxidants mainly by:

1. Raising the pH of the fat to inhibit oxidation
2. Donating hydrogen to lipid radicals faster than BHA
3. Chelating metal ions that catalyse initiation
4. Quenching singlet oxygen like carotene

9 · Antioxidants: natural and synthetic · hard

Why does ghee prepared at a higher clarification temperature usually keep better?

1. Higher temperature adds iron from the pan, which stabilises the fat against oxidation in storage
2. More phospholipids pass into the fat and Maillard products with antioxidant activity form
3. Higher temperature converts cholesterol into tocopherol
4. Higher temperature removes all unsaturated fatty acids from the fat

10 · Cholesterol in milk and its reduction · hard

How does beta-cyclodextrin remove cholesterol from milk or butter oil?

1. It dissolves cholesterol in supercritical carbon dioxide, which is then vented from the vessel
2. It oxidises cholesterol to carbon dioxide and water
3. It hydrolyses cholesterol esters into free fatty acids
4. It binds cholesterol in its hydrophobic cavity, and the complex is removed by centrifugation