FSSAI Food Analyst and Junior Analyst Examinations Milk Composition & Physical Properties: practice questions

1 · Variation with breed, feed, season, lactation stage and mastitis · hard

A milk collection centre notices that a farmer's evening milk is consistently richer in fat than his morning milk. Cows are milked at 5 a.m. and 3 p.m. What is the most likely explanation?

1. The shorter interval before the afternoon milking gives a smaller, fat-richer yield
2. The cows are milked incompletely in the afternoon, which raises the fat of that milking
3. The afternoon feed contains more fibre, which raises fat within hours
4. Evening milk is warmer, and warm milk always tests higher in fat

2 · Colostrum and abnormal milks · medium

Milk from a cow treated with an intramammary antibiotic is sent to a cheese plant before the withdrawal period ends. Apart from the public-health concern, what technological problem is expected?

1. Faster rennet coagulation, giving an over-firm curd that is hard to cut
2. An increase in lactose that causes browning on heating
3. A higher fat content that overloads the separator
4. Inhibition of the starter culture, giving slow acid development

3 · Colostrum and abnormal milks · hard

A sample shows a metallic, cardboard-like flavour. The farm uses unlined copper-alloy fittings and stores milk in clear containers. Which defect is this, and what drives it?

1. Malty flavour from growth of Lactococcus lactis var. maltigenes
2. Rancid flavour from lipolysis of milk fat caused by lipoprotein lipase
3. Oxidised flavour from lipid oxidation catalysed by copper and light
4. Feed flavour absorbed from silage odours in the milking shed

4 · Density and specific gravity; lactometer readings · easy

A Quevenne lactometer reads 27 in milk at 56 degrees Fahrenheit. What is the corrected lactometer reading at 60 degrees Fahrenheit?

1. 27.0
2. 27.4
3. 22.6
4. 26.6

5 · Density and specific gravity; lactometer readings · medium

Using Richmond's formula for readings at 60 degrees Fahrenheit, what is the SNF of milk with 3.5 per cent fat and a corrected lactometer reading of 26.6?

1. 7.53 per cent
2. 7.39 per cent
3. 11.03 per cent
4. 6.79 per cent

6 · Acidity and pH; titratable acidity · hard

Buffalo milk at a collection centre shows 0.16 per cent titratable acidity but passes the clot-on-boiling and alcohol tests. What is the most reasonable interpretation?

1. The milk is sour and should be rejected at once, because any TA above 0.14 per cent proves souring in buffalo milk
2. The higher protein and phosphate of buffalo milk raise natural acidity; the milk is not necessarily sour
3. The milk is colostral, because only colostrum exceeds 0.14 per cent
4. The milk has been watered, because watering raises titratable acidity

7 · Buffer capacity and acid-base equilibria · hard

Why does milk concentrated by ultrafiltration acidify more slowly during fermentation than normal milk?

1. Ultrafiltration removes all citrate, the main buffer of normal milk
2. Lactose is removed completely in the permeate, so starter bacteria cannot produce any acid
3. Proteins and colloidal calcium phosphate are concentrated, raising buffer capacity
4. The membrane adds sodium hydroxide that neutralises the lactic acid

8 · Electrical conductivity, refractive index and thermal properties · medium

How much heat is needed to raise 5,000 kilograms of milk from 4 to 72 degrees Celsius, taking specific heat as 3.9 kilojoules per kilogram per kelvin and ignoring losses?

1. 1,421,400 kilojoules
2. 1,404,000 kilojoules
3. 1,326,000 kilojoules
4. 19,500 kilojoules

9 · Oxidation-reduction potential · medium

In the resazurin test, the colour of milk changes as the bacterial load increases in which sequence?

1. Green to yellow to brown
2. Blue to pink to colourless
3. Colourless to pink to blue
4. Pink to blue to yellow

10 · Colour and optical properties of milk · medium

Milk sold in clear bottles develops a burnt-feather off-flavour after a few hours in sunlight. Which reaction is responsible?

1. Lipolysis of milk fat by lipoprotein lipase
2. Riboflavin-sensitised oxidation of methionine to methional
3. Fermentation of lactose to lactic acid by bacteria
4. Maillard reaction between lactose and lysine