food tests - practical

what is the first step to preparing a food sample for a food test?

grind up the food using a pestles and mortar

what is the second step to preparing a food sample for a food test, after grinding it up?

add water and stir to dissolve the food

what is the third and final step to preparing a food sample for a food test, after adding water?

filter the mixture to remove the lumps of food, and then the remaining solution can be used for testing

what do we call the test for reducing sugars (like glucose) ?

benedict’s test is the test for reducing sugars

what do we call the test for starch?

the iodine test is for starch

what do we call the test for proteins?

the biuret test is the test for proteins

what are the two tests for lipids?

the emulsion test, and the sudan iii stain test

what is the first step to carrying out the benedict’s test?

add 10 drops of benedict’s solution to your food sample

what is the second and final step to carrying out the benedict’s test?

heat in a water bath at 75 degrees celsius for five minutes, and then look for a colour change

what colour change are you looking for in the benedict’s test?

a colour change from blue (no sugar), to green (low conc. reducing sugar), to orange (medium conc. reducing sugar), to brick red (high conc. reducing sugar) - this indicates hat reducing sugars are present

how would you perform the test for starch and what colour change would you look for?

take your food sample and add a few drops of iodine - if starch is present it will change from browny-orange to blue-black

how would you perform the test for protein and what colour change would you look for?

take your food sample and add an equal volume of biuret solution - if protein is present it will change from blue to purple

how would you perform the test for starch and what change would you look for?

place 5cm³ of your food sample in a test tube, add 3 drops of sudan iii stain solution, and then gently shake it - if a red layer separates out on top, then lipid was present