Testing Compounds in Foods: Lipid, Protein, Sugar, Starch

[JimmyRay]

Hi we did a lab today for testing compounds in foods...

So basically the only way to detect if a lipid is present is by transparency? Like we used a paper towel, we added a few drops of the substance to the paper towel and then rubbed it today, if it was transparent it tested positive for lipid...

Is that the only indicator?

Is anyone familliar with the indicators for protein, sugar and starch? (Just want to see if I can check my results).

We tested these on Apple, Orange, Milk and Butter. For lipids we also used oil (positive), for protein we used albumin (I got negative), for sugar we used glucose (positive), for starch test we used.. starch (positive)

 

[DocToxyn]

Take a look at some of the more common assays for protein such as lowry, coomassie blue, bicinchoninnic acid (BCA). They are basically dye-binding assays which will quantify total protein in solution. A search on google scholar would be a place to start or check out an assay provider like Pierce.

 

[ravenprp]

Hi there,

Yes, the transparency test is one way to detect the presence of lipids in a substance. Lipids are non-polar molecules, meaning they do not mix well with water. Therefore, when they are placed on a paper towel, they will not dissolve and will appear as a translucent spot.

There are other indicators for lipids as well, such as the Sudan III or IV test, which involves adding a specific dye to the substance and observing a color change. However, the transparency test is a quick and easy way to detect the presence of lipids.

For protein, the most common indicator is the Biuret test, which involves adding a solution of copper sulfate and sodium hydroxide to the substance and observing a color change. If the substance turns purple, it indicates the presence of proteins.

For sugars, the most common indicator is the Benedict's test, which involves adding a solution of Benedict's reagent to the substance and heating it. If the substance turns orange or red, it indicates the presence of reducing sugars.

For starch, the most common indicator is the iodine test, which involves adding a few drops of iodine solution to the substance. If the substance turns blue-black, it indicates the presence of starch.

It's great that you were able to perform these tests on different foods and obtain positive results for lipids, proteins, sugars, and starch. These tests are important in determining the nutritional content of foods and can also be used to identify unknown substances. Keep up the good work!