IIT JEE 2006 Sample Question Paper

Passage 2

When food is cooked, only some of the nutrients are preserved. Food scientists performed two experiments to study the retention of vitamin C after potatoes were cooked. The scientists measured the retention of ascorbic acid (AA) and dehydroascorbic acid (DAA). The sum of the amounts of AA and DAA equals the total amount of Vitamin C.

Experiment 1
In this experiment, potatoes were peeled and then fried. The following table shows the stability of ascorbic acid and dehydroascorbic acid after frying. The concentrations of AA and DAA are given in milligrams per 100 grams of dry potato.

Sample DAA
(mg/100g) AA
(mg/100g) Total Content of vitamin C
(mg/100g)

Raw, peeled potatoes before frying 7.4 44.6 52.0

Fried potatoes
140^o for 10 min
140^o for 20 min
140^o for 30 min
180^o for 5 min
29.7
33.7
42.7
42.8
20.6
7.3
0
0
50.3
41.0
42.7
42.8

Experiment 2
In this experiment, potatoes were peeled and then boiled in water with varying concentrations of NaCl. The following table shows the stability of ascorbic acid (AA)and dehydroascorbic acid (DAA) after boiling.

Sample DAA
(mg/100g) AA
(mg/100g) Total Content of vitamin C
(mg/100g)

Raw peeled potatoes
Coocked in water
Coocked in 1% NaCl
Coocked in 5% NaCl
Coocked in 10% NaCl 7.4
9.0
9.1
7.1
5.8 43.1
17.1
13.1
11.2
8.9 50.5
26.1
22.2
18.3
14.7

Q. 6 Which of the following statements accurately reflects the experimental results?

There is more DAA in fried potatoes than in raw, uncooked potatoes.
There is more AA in fried potatoes than in raw, uncooked potatoes.
There is more total vitamin C content in fried than in raw, uncooked potatoes.
There is more AA in fried potatoes compared with uncooked potatoes, but only if they are fried at 140oC or lower.

Answer: A

Description: The concentration of DAA in uncooked potatoes is 7.4 mg/100 grams of dry matter. In the four examples of frying, the DAA concentrations ranged from 29.7 to 42.8, clearly indicating an increase.

Q. 7 If some potatoes were boiled in a 10% NaCl solution, and there were 300 grams of potato left, how many milligrams of vitamin C would there be?

14.7
17.4
26.7
44.1

Answer: D

Description: After potatoes are boiled in a 10% NaCl solution, there are 14.7 milligrams of vitamin C per 100 grams of potato. Therefore, if there were 300 grams of potato, there would be 14.7 * 3 = 44.1 milligrams of vitamin C.

Q. 8 What concentration of ascorbic acid would you expect to see if potatoes were fried for 45 minutes at 140oC?

0 mg/100 grams
7.3 mg/100 grams
20.6 mg/100 grams
There is insufficient evidence to answer

Answer: A

Description: Although this question does break our rule concerning extrapolation, it is reasonable to infer from the given data that the ascorbic acid will be depleted. The data show a decreasing concentration until there is 0 mg/100 grams after 30 minutes of frying. Unless there is some process by which AA is suddenly created as the frying proceeds, the concentration will stay at zero.

Q. 9

Answer: D

Description: The table tells us how much Vitamin C will be retained. The concentration will be about 18 mg/100 grams of potato after cooking in a 5% NaCl solution, whereas for the uncooked potato, the vitamin C content is 50 mg per 100 grams. That means about 36% of the Vitamin C is retained. But this means that about 64% is lost.

Q. 10 All of the following explanations could account for the different pattern of DAA retention when comparing frying and boiling except:

When immersed in water, the AA is less likely to oxydize to become DAA.
When immersed in water, DAA is hydrolized to become 2,3-diketogluconic acid.
Frying increases the likelihood for DAA to break down into other compounds.
Frying dries out the potatoes and reduces the tendency for DAA to hydrolyze.

Answer: C

Description: If it were true that frying increased the likelihood of DAA breaking down into other compounds, then we would expect to see less DAA when frying than when boiling. But the opposite is true, so this explanation must be false.