ICAR AIEEA-PG Whey & Dairy By-product Utilisation: practice questions

1 · Casein and caseinates; co-precipitates · medium

1,000 kg of skim milk with 2.7% casein gives acid casein with 96% recovery; the dried casein contains 10% moisture. What mass of casein is produced?

1. 23.3 kg
2. 28.8 kg
3. 27.0 kg
4. 25.9 kg

2 · Whey disposal problem: BOD and COD · medium

If a cheese plant recovers its whey protein by UF but discharges the 5,000 L/day of permeate, whose BOD is still about 40,000 mg/L because of lactose, what BOD load remains?

1. 200 kg/day
2. 20 kg/day
3. 200,000 kg/day
4. 0 kg/day

3 · Types and composition of whey · easy

Which is the main solid component of whey?

1. Milk fat, which passes from the curd into the whey
2. Lactose
3. Whey protein, which makes up most of the solids
4. Casein, which stays in suspension after the curd forms

4 · Types and composition of whey · medium

Acid whey differs from sweet whey in having:

1. More lactic acid, calcium and phosphate
2. More caseinomacropeptide released by chymosin action
3. A higher pH, close to that of fresh milk at 6.6
4. Much more fat and casein carried over from the curd

5 · Whey disposal problem: BOD and COD · medium

Which component contributes most of the BOD of whey?

1. Milk fat, because it floats and blocks aeration
2. Lactose
3. Whey protein, because it is degraded fastest
4. Minerals, because they consume dissolved oxygen

6 · Whey beverages and whey cheese: ricotta, ricotta-type and brown whey cheese · medium

Why is milk or cream often added to whey for ricotta?

1. To raise the low yield and add richness
2. To supply rennet for coagulating the whey proteins
3. To lower the coagulation temperature to 30 °C
4. To remove lactose from the finished cheese

7 · Whey powder and demineralised whey · easy

Why is whey concentrate pre-crystallised before spray drying?

1. To denature the whey proteins before they reach the dryer
2. To remove all the minerals from the whey concentrate
3. To increase the fat content of the powder
4. To make a non-caking, less hygroscopic powder

8 · Lactose manufacture and refining · easy

Edible lactose crystallises from concentrated whey or permeate mainly as:

1. Lactulose crystals
2. Amorphous glassy lactose
3. Alpha-lactose monohydrate
4. Beta-lactose anhydrous above 100 °C

9 · Casein and caseinates; co-precipitates · medium

Sodium caseinate is made by:

1. Fermenting whey with a sodium-tolerant yeast culture for days
2. Heating milk with sodium chloride
3. Neutralising acid casein with sodium hydroxide
4. Adding salt to rennet casein curd

10 · Fermentation of whey: ethanol, biogas, single-cell protein · easy

Which yeast is commonly used to ferment whey lactose to ethanol?

1. Penicillium roqueforti
2. Kluyveromyces marxianus
3. Lactobacillus bulgaricus
4. Saccharomyces cerevisiae without modification