Biochemical Tests AS Biology

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BIOCHEMICAL TESTS

Proteins - add biurettes reagent to the sample. If protein is present, clear colour change from blue to purple.

Reducing Sugarsadd Benedict’s reagent to the sample. Heat in bunsen or water bath. If reducing sugars are present, clear colour change from blue -> orange red precipitate.

Lipidsdissolve sample in ethanol. Slowly pour the solution into the water. If lipids are present a white emulation forms on the surface.

Starchadd iodine solution to the sample. If starch is present clear colour change from orange red to blue black.

Non reducing sugarsdo the reducing sugars test. Add Benedict's to the sample & heat. You get a negative result. Take a fresh sample and add heat with dilute acid. Bring to the boil. This hydrolyses it! Then, neutralise it with an alkali and test with pH paper. Add Benedict's and heat again. If non reducing sugars are present, clear colour change from blue to an orange red precipitate.

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