in this video we're going to run through the different food tests and we're going to cover all the ones you need to know for your gcse biology practicals so we'll cover the benedict's test which is for sugars the iodine test for starch the buret test for proteins and the sudan 3 test for lipids and for those of you doing the edexcel course we'll cover the emulsion test for lipids as well now one thing that all of these tests have in common is you need to prepare your food sample for this you first need to get your piece of food and break it up using a water and pestle then you need to put this crushed food into a beaker with some distilled water and stir it with a glass rod until some of it dissolves the last thing we need to do is filter out the solution using a funnel that's been lined with filter paper to get rid of all the solid bits of food that we don't need and this solution that we end up with will be our sample that we can use for the food tests sugars are the small units that all carbohydrates are made of and they can be split into two types reducing sugars and non-reducing sugars now you don't really need to know the difference between these two but just remember that the benedict's test only tests for reducing sugars so to do this test you first prepare your food sample like we did a minute ago and transfer five centimeters cubed of that sample to a test tube you also need to prepare a water bath and set it to 75 degrees celsius once your water bath is ready you can add about 10 drops of benedict solution to your test tube and place it in the water bath for five minutes for safety reasons though you should use a test tube holder to place it in the water bath and point the tube away from you and anybody else now if no reducing sugars are present then a solution will stay blue but if there are reducing sugars present it should change to green yellow or even brick red depending on the concentration just like sugars starch is a type of carbohydrate but it's a much larger and more complex molecule luckily though the test for it is much simpler all you do is take five centimeters of your food sample and add a few drops of iodine solution this will turn the solution a browny orange color next you get a gentle shake and if a sample did contain starch the solution would change from that brownie orange color to a blue black color and as all we did here was add iodine we simply call this the iodine test the buret test meanwhile is a test for proteins in this one you add two rather than five centimeters cubed of your sample to a test tube and then add another two centimeters of the burette solution to your sample turning in blue before gently giving it a shape and if the food sample did contain protein the solution would change from blue to pink or purple now if you're doing the edexcel course you might need to be a bit more specific and instead of just adding directory agent add potassium hydroxide followed by copper sulfate when it comes to lipids we do something called the sudan 3 test for this you need 5 centimeters cubed of your food sample but importantly you don't need to have filtered it then you add three drops of the sudan 3 stain solution to the test tube and gently shake it if the lipid was present it should get stained by the sudan 3 solution and as the lipid separates from the water because it's not soluble you'll see there's a bright red layer at the top if you're doing the ed excel course then you might need to know about the emulsion test flip is instead in this case all you do is take your food sample add two centimeters cubed of ethanol and shake it vigorously then you add an equal volume of distilled water and if it goes a cloudy white color it means that lipid was present if there isn't any cloudy white color then there wasn't any lipid and those are all the tests that you need to know for the food test practical if you found that useful then give us a like and we'll see you next time