Reducing and non reducing sugar food test

what molecules are reducing sugars (5)

glucose

fructose

galactose

disaccharides- maltose and lactose

non reducing sugar example (2)

sucrose

all polysaccharides- glycogen and cellulose

test for reducing sugars 4 steps

1. put 2cm cubed of food sample into test tube

2. add 3cm cubed of benedict’s agent

3. 3. heat for 5 mins (water is boiled)

4. 4. observe colour change blue to green, orange, brick red

non reducing test (5 steps)

1. test for reducing sugars if result is negative you don’t have reducing sugars

2. put 2cm cubed of sample into test tube

3. add cm cubed of dilute HCl and boil for 5 minutes . this hydrolyses non reducing sugars into reducing sugars

4. add sodium hydrogen carbonate, (alkaline substance neutralises acidic solution)

5. test for reducing sugars, if test is positive, reducing sugars should form a brick red precipitate.

More precise measurement example (7)

use a colimeter

measures absorbance of light by a solution

low absorbance: low concentration

high absorbance: high concentration

Filter solution and weigh solid

lower mass of precipitate: less sugar

higher mass of precipitate: more sugar

starch test (5)

put 2cm cubed of sample into test tube

add a few drops of iodine solution

shake

negative test stays orange

positive test blue black