Benedicts Test for Reducing Sugars: Tube Solution/food Color reaction to Benedic
ID: 9440 • Letter: B
Question
Benedicts Test for Reducing Sugars:Tube Solution/food Color reaction to Benedicts solution Presence of reducing sugar (green/reddish orange color)
1 1ml distilled water
2 good pinch glucose powder
3 good pinch table sugar (sucrose)
4 2 drops honey
5 finely chopped onion
6 finely chopped fruit
7 1ml milk
8
9
10
Which of the above solutions was included as your negative control? [1 pt]
Which of the above solutions was included as your positive control? [1 pt]
Which of the above foods/solutions tested positive for sugars? [4 pts]
Explain why sucrose (table sugar) yielded the result above. [2 pts]
What does this tell you about the way sugars are stored, for example in onions? [2 pts]
Sugar is actually a common name for glucose. Glucose is stored as starch in onions as it is a bulb present in plants.
Would you use the Benedicts test to investigate if a cake mix were sugar free? Explain your answer [2 pts]
The benedicts test cannot be used to determine if a cake mix is sugar free or not. This is because benedicts test is used to determine the presence of reducing sugars like maltose and lactose. Fructose also gives a positive test. We use sucrose in food so we cannot detect the presence or absence of sucrose in the cake mix
Iodine Test for Starch:
Depression Number Solution/food Color reaction to iodine solution Presence of starch (bluish-black color)
1 ½ ml distilled water
2 pinch glucose powder
3 pinch cornstarch
4 ½ ml egg white
5 finely chopped onion
6 Finely chopped potato
7 1 drop honey
8
9
10
Which of the above solutions was included as your negative control? [1 pt]
Which of the above solutions was included as your positive control? [1 pt]
Which of the above foods/solutions tested positive for starch? [4 pts]
Did any of the animal sources contain starch? Explain your answer. [2 pts]
Did any of the same foods test positive for both reducing sugars (Benedicts Test) and starch (Iodine Test)? Explain your answer. [4 pts]
Proteins:
Tube Solution/food Color reaction to Biuret Reagent Presence of protein (violet color)
1 2ml distilled water
2 2ml milk
3 2ml egg white
4 2ml egg yolk
5 2ml honey
6
7
8
9
10
Which of the above foods/solutions tested positive for protein? [4 pts]
Did any of the foods/solutions that tested positive for protein also test positive for reducing sugars (Benedicts Test) or starch (Iodine test)? Explain your answer. [2 pts]
How is the structure of proteins in plants and animals similar? [3 pts]
How are proteins in plants and animals different? [3 pts]
Lipids:
Test Solution/food Grease spot indicating the presence of lipid
1 1ml distilled water
2 Oil-vinegar salad dressing
3 walnut
4 Egg white (wipe away excess)
5 Egg yolk (wipe away excess)
6
7
8
9
10
Which of the foods tested were positive for the presence of lipid? [4 pts]
Part 2 – Tracking Macromolecules in Your Diet
Include a copy of your “nutrient intake” and record the following nutrient intakes in the space below. NOTE: Nutrient Intake is the name of the report generated at www.MyPyramid.gov [10 pts]
Kilocalories Percent Total Recommended
Energy Intake Intake
Carbohydrate ___________ ______________ 45-65%
Protein ________________ ______________ 10-35%
Total Fat _______________ _______________ 20-35%
Show your calculations in the space below
How did your consumption of macronutrients compare to the recommended intake?
Explanation / Answer
Benedict’s test is used to identify the presence of reducing sugar. The Benedict’s reagent is prepared by copper sulfate, sodium carbonate, and sodium citrate, which is used to identify the reducing sugar. The examples of reducing sugar are glucose, fructose, galactose etc. This test is both qualitative and quantitative test.
The control used in this test is mostly water. The color of the Benedict’s reagent is blue. The result is considered to be positive when the color of solution turns from blue to green, yellow, orange, or red. The range of colors indicates intensity of reducing sugar in the solution.
In the above solutions, the negative controls include 1ml distilled water and good pinch table sugar (sucrose).
In the above solutions, the positive controls include good pinch glucose powder, finely chopped onion, 2 drops honey, finely chopped fruit, and 1ml milk.
Milk contains a reducing disaccharide called lactose. Lactose is formed by glucose and galactose. The honey contains hydrolyzed sucrose, which includes glucose and fructose. Similarly, onion and fruits contains glucose, fructose, and sucrose. Except sucrose remaining two sugars are reducing sugars in onions and fruits. Thus, onion and fruit solutions give positive result with Benedict’s reagent.
Sucrose is a non-reducing sugar where the glucose and fructose are linked via C1 on glucosyl sub-unit and C2 on fructosyl unit. In sucrose, the reducing ends are involved in bond formation. Thus, they give negative result with Benedict’s reagent.
In the given test, onions give positive result with Benedict’s reagent. This indicates that the onions contain reducing sugars.
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