ICAR AIEEA-PG: Dairy Science (group 16) and Dairy Technology (group 17) · India · NTA for ICAR
Original practice questions written to the published syllabus · not past papersYoghurt, dahi and the world's fermented milks: process, cultures, texture, defects and shelf life.
In the exams: ICAR AICE subjects 34 Unit 7 and 36 Unit 5; ICAR AIEEA-PG group 16 (dahi, yoghurt, kefir, koumiss, Bulgarian milk, cultured buttermilk, leben, yakult); GATE XL-U Section 2 (curd, yoghurt)
ICAR AIEEA-PG — Dairy Science (group 16)
Microbiology of fermented milks and the probiotic concept in dahi, yoghurt, kefir, kumiss, Bulgarian milk, cultured buttermilk, leben and similar products; chemistry of milk fermentation. Expect direct MCQs on the organisms of each product, protocooperation, flavour compounds (acetaldehyde, diacetyl) and defects.
How our questions for ICAR AIEEA-PG spread across the units of Fermented Milks Technology. Difficulty: 17 easy, 21 medium, 5 hard.
| Dahi, misti dahi, shrikhand and lassi | 10 | |
| Process steps and their effect on texture | 7 | |
| Cultured buttermilk and sour cream | 5 | |
| Classification of fermented milks worldwide | 4 | |
| Kefir, koumiss and yeast-lactic fermented milks | 4 | |
| Yoghurt: set, stirred, drinking and strained types | 3 | |
| Syneresis, post-acidification and other defects | 3 | |
| Skyr, labneh and other concentrated fermented milks | 2 | |
| Fruit preparations and flavouring | 2 | |
| Probiotic fermented milks | 2 | |
| Shelf life of fermented milks | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Shrikhand is made from 40 kg of chakka. How much sugar must be added so that sugar is 45% of the finished shrikhand?
C. 32.7 kg
S ÷ (40 + S) = 0.45 gives S = 0.45 × 40 ÷ 0.55 = 32.7 kg. 18.0 kg is 45% of the chakka, not of the final product; 48.9 kg inverts the fractions; 12.4 kg uses the wrong denominator.
Further reading: De, Outlines of Dairy Technology
Under the Codex standard, yoghurt is made with which pair of organisms?
A. Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus
Codex yoghurt uses S. thermophilus with L. bulgaricus. The lactococcus-leuconostoc pair is a buttermilk culture; L. acidophilus with bifidobacteria is a probiotic culture; L. bulgaricus with K. marxianus is kumys.
Further reading: Tamime (ed.), Fermented Milks
Which fermented milk is classed as yeast-lactic?
B. Kefir
Kefir contains lactic acid bacteria and yeasts. Yoghurt, cultured buttermilk and acidophilus milk are lactic fermentations only.
Further reading: Tamime (ed.), Fermented Milks
In the yoghurt culture, which organism produces most of the acetaldehyde that gives the characteristic flavour?
D. Lactobacillus bulgaricus
L. bulgaricus is the main acetaldehyde producer. S. thermophilus contributes less; leuconostocs and yeasts are not yoghurt organisms.
Further reading: Tamime and Robinson, Yoghurt: Science and Technology
In yoghurt protocooperation, what does S. thermophilus supply that stimulates L. bulgaricus?
A. Formic acid and carbon dioxide, and a lower oxygen level
The streptococcus provides formic acid, CO2 and reduced oxygen; the lactobacillus, being more proteolytic, supplies peptides and amino acids to the streptococcus.
Further reading: Tamime and Robinson, Yoghurt: Science and Technology
How does set yoghurt differ from stirred yoghurt in manufacture?
A. It is fermented in the retail cup
Set yoghurt incubates in the cup; stirred yoghurt is fermented in tanks, broken and then filled; drinking yoghurt is broken down further; strained yoghurt loses whey.
Further reading: Tamime and Robinson, Yoghurt: Science and Technology
Household dahi in India is traditionally made by:
B. Inoculating boiled, cooled milk with a little of yesterday's dahi
Back-slopping gives an undefined mixed culture. Rennet and pressing make cheese; citric acid at high temperature makes paneer.
Further reading: De, Outlines of Dairy Technology
Buffalo milk dahi is typically firmer than cow milk dahi because buffalo milk has:
A. Higher casein, fat and total solids
Higher solids, especially casein, give a firmer acid gel.
Further reading: Tamime and Robinson, Yoghurt: Science and Technology
The buttery aroma of cultured buttermilk comes mainly from:
B. Diacetyl made from citrate
Citrate-fermenting aroma organisms produce diacetyl. Acetaldehyde is the yoghurt note; ethanol comes from yeasts; propionic acid from propionibacteria.
Further reading: Tamime (ed.), Fermented Milks
Which organisms in a buttermilk culture convert citrate to diacetyl?
A. L. lactis biovar diacetylactis and Leuconostoc mesenteroides subsp. cremoris
The citrate-positive lactococcus and leuconostoc are the aroma producers in mesophilic cultures.
Further reading: Tamime (ed.), Fermented Milks
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