Food Tests

Protein

Protein with biuret added turns purple. (Biuret pronounced buy-your-et)

Protein mixed with biuret solution should turn purple

The protesting teenagers (proteins) said: “We’ll buy your eggs” (biuret), but the shop would not sell them any because they would be used for protesting. The protesting teenagers turned purple with rage.

The test for protein:

Protein turns biuret solution purple when added and shaken with chopped food

Glucose

Add Benedict’s solution to some food in a test tube. Boil for 5 minutes. If glucose is present the colour turns green (if only trace amounts present), then orange-red if the concentration of glucose is greater.

Glucose added with benedicts solution should turn green then orange and red

If glucose is drunk by him, Big Ben predicts (Benedict’s) that the traffic lights at his foot will change to green then orange and red.

The test for glucose:

Benedict's solution added to chopped food in a test tube should be boiled, and should turn green with traces of glucose, then orange or red with high concentrations of glucose

Starch

Add orange-brown iodine to some food. If starch is present the colour changes to blue-black.

Iodene added to food should turn blue/black showing the presence of starch

I could see stars (starch) after I was beaten black and blue, just because I dined (iodine) on oranges!

The test for starch:

Food such as wheat based products like bread and cerial with iodene added should turn blue/black showing the presence of starch

Fats (Lipids)

Fats (lipids) go cloudy white when mixed with ethanol and water.

Fats should go cloudy when ethanol and water is added

Fat mama (fats) and her white poodle (ethanol) are in the rain (water) and Fat Mama’s lips (lipids) turn white. To remember that white poodle means ethanol, click here

The test for lipids.

Dissolved food in ethanol filtered into a text tube then add water the emulsion should turn white if lipids are present

Dissolve the food in ethanol and filter. Add water. Observe a white emulsion if lipids are present.