Why is there a colour change in a reagent when a nutrient is present in food tests ?I'm trying to decide if it has anything to do with hard foods having to be crushed and water added when being...

Why is there a colour change in a reagent when a nutrient is present in food tests ?

I'm trying to decide if it has anything to do with hard foods having to be crushed and water added when being tested with a reagent.

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bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

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Any time you are doing a chemistry lab that involves a colour change, the colour change is being used as an indicator.  If one is conducting food tests, the colour change is probably indicating a presence of one of the three main constituents of foods, those being a carbohydrate, a protein, or a fat.  Carbohydrates may be broken down into two subgroups, sugars and starches.  Colour changes have long been used in the chemistry lab to indicate presence of a certain substance.  For example potassium cyanate (KSCN) will turn a fiery blood red in the presence of iron (Fe+2) ions.  Bromine solution, which is a deep orange in color, will turn a dark, bluish black color when it detects the presence of starch, such as that present in a potato.  So the colour change is part of an interaction with that specific substance, and the colour change is a physical observation used to detect the presence of that substance.

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