Of the following substances, which would react positively with Biuret's, Lugol's, and Benedict's?
1. water 2. starch 3. glucose 4. maltose 5. sucrose 6. fructose 7. galactose 8. albumin 9. hamburger juice 10. onion juice 11. milk 12. potato juice 13. lactose
3.glucose
Describe any limitations to the usefulness of protein, sugar, fats and starch test for food sample
To determine which substances would react positively with Biuret's, Lugol's, and Benedict's tests, we need to understand the principles behind each test.
1. Biuret's test: It is used to detect the presence of proteins. Biuret's reagent reacts with the peptide bonds in proteins, resulting in a color change from blue to purple.
2. Lugol's test: It is used to detect the presence of starch. Lugol's solution reacts with the starch, forming a dark blue color.
3. Benedict's test: It is used to detect the presence of reducing sugars, such as glucose and maltose. Benedict's reagent reacts with reducing sugars, causing a color change from blue to green, yellow, orange, or red, depending on the amount of sugar present.
Now, let's analyze each substance based on these tests:
1. Water: It does not contain proteins, starch, or reducing sugars, so it would not react positively with any of the tests.
2. Starch: It would react positively with Lugol's test, forming a dark blue color.
3. Glucose: It is a reducing sugar, so it would react positively with Benedict's test, causing a color change.
4. Maltose: It is also a reducing sugar, so it would react positively with Benedict's test.
5. Sucrose: It is a non-reducing sugar, so it would not react positively with Benedict's test.
6. Fructose: It is a reducing sugar and would react positively with Benedict's test.
7. Galactose: It is a reducing sugar and would react positively with Benedict's test.
8. Albumin: It is a protein and would react positively with Biuret's test, forming a purple color.
9. Hamburger juice: It may contain proteins, so it would react positively with Biuret's test if proteins are present.
10. Onion juice: It may contain reducing sugars or proteins, so it could potentially react positively with Benedict's or Biuret's test.
11. Milk: It contains proteins, so it would react positively with Biuret's test.
12. Potato juice: It may contain proteins, so it would react positively with Biuret's test if proteins are present.
13. Lactose: It is a reducing sugar and would react positively with Benedict's test.
In conclusion, the substances that would react positively are:
- Biuret's test: Albumin, hamburger juice, onion juice, milk, potato juice.
- Lugol's test: Starch.
- Benedict's test: Glucose, maltose, fructose, galactose, and lactose.