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Summary IGCSE-Biology-Food Tests
IGCSE-Biology-Food Tests: Summary of Food test in IGCSE Biology triple award.
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Food Tests:Scientists need to test food for specific nutrients they contain. Food tests are qualitative: they provide
observations about what nutrients are present, but not the amounts of them (quantitative). There are 4
things they can test for: Starch, Sugars (glucose), Proteins, Lipids.
Testing for STARCH:
You can test for starch using an iodine solution. A positive result will cause the iodine to change colour
from yellow-brown to blue-black.
Testing for GLUCOSE:
You can test for glucose using benedict's solution. You need to dissolve the glucose in water, and add
Benedict's. This needs heating in a water bath. If glucose is present, the benedicts will turn from clear
blue to a cloudy orange colour (brick red).
Fructose will also give a similar result with benedict’s solution as glucose, however sucrose will not.
The test works with glucose and fructose
because they are reducing sugars. They
are able to reduce Copper(II) sulfate
(blue) to copper(I)oxide. The amount of
sugar can also be determined, as
benedicts will change different colours
depending on the amount of sugar
present.
Testing for PROTEIN:
You can test for protein using biuret solution. You need to mix the protein in water, and add biuret
solution. If protein is present, the biuret solution will turn from blue to purple.
Testing for LIPIDS:
Lipids are insoluble in water, but are soluble in ethanol. You can shake a test tube of oil and ethanol, to
dissolve the oil, then add this to water. The lipid will precipitate out, forming an emulsion
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