Detection of proteins in natural products
Proteins in potatoes
Grind with a grater one potato and add twice the amount of water. Allow to settle and dissolve for 15 minutes and filter.
Take two pipettes of the filtrate and do the Biuret-test. Bring the rest of the filtrate to boil. Hereby the albumen of the potato will flocculate. Filter again and do with the residue Millon's test and the xanthoprotein test.
Observations? - Explanations?
Comparison of wool, cotton and silk
Wool consists of keratin which means fibrous proteins which contain mainly the AA tyrosine, cysteine, phenylalanine and tryptophane .
Silk mainly consists of fibroin which contains to 60% alanine and glycine and to more than 10% tyrosine. The sulphurcontaining cysteine is (nearly) completely missing .
Cotton consists only of cellulose.
Try to distinguish between these products by the following tests: Xanthoprotein; Millon; Leadsulfide (refer to chapter AA)
Note the results in a table! - Do they prove the facts given above?