Food Tests

Question 1

Benedict’s test for reducing sugars ?

what is not a reducing sugar?

what test is this, quantitative or qualitative? and why

Answer 1

all monosaccharides and disaccharides are reducing sugars except sucrose

1) a small amount of the sample is placed in a test tube with the same volume of benedict’s solution

2) this is heated to 95°c in a water bath

3) a brick red or orange precipitate is formed if reducing sugar present

it is a qualitative test as it does not allow you to compare results from other samples, it simple gives you a positive or negative result

Question 2

what is a quantitative test?

Answer 2

a test which produces a colour whose intensity depends on the concentration of the reducing sugar in a solution

Question 3

quantitative benedict test

Answer 3

this is carried out to obtain numerical data to compare the concentration of reducing sugar in different samples

it is an objective test

this method can also be used to find the concentration of an unknown sample

1) perform benedict’s test on samples with a known concentration

2) control variables must be standardised, same volume of benedict’s and sample solution. heat both at same time and temperature

3) use a colorimeter to find the absorbance of the known solutions

4) plot a graph with known concentrations (x) and absorbance value (y)

^ calibration curve

5) repeat the benedicts with unknown sample

6) use the absorbance value to find the concentration on the the calibration curve

Question 4

test for proteins

Answer 4

1) add biuret reagent
2) blue—> purple/lilac