Qualitative Tests for Carbohydrates

Study Notes

Molisch Test: A general test for the presence of carbohydrates, indicating a positive result with a violet ring.
Glucose & Sucrose Molisch Test: Both yield a positive result with a violet ring.

Iodine Test: Used to detect starch by adding potassium iodide solution; a positive result shows a color change to purple/black.
Glucose, Water, Maltose Iodine Test: These do not yield a positive result, indicated by a negative (yellow) outcome since they are not polysaccharides.
Starch Iodine Test: A positive response is indicated by a blue-black color.

Benedict's Test: A biochemical reaction to identify reducing sugars; a positive result appears brick red.
Positive Reducing Sugars: Glucose, maltose, and fructose all produce a brick red result with Benedict's.
Negative Reducing Sugars: Sucrose and starch remain blue, indicating they are not reducing sugars.

Barfoed's Test: Specifically tests for monosaccharides; a positive result for glucose and fructose is brick-red.
Maltose Barfoed's Test: Yields a positive result after 10 minutes, indicating it is a disaccharide.
Negative Monosaccharides: Sucrose and starch both return a blue result, indicating they are not monosaccharides.

Seliwanoff's Test: Distinguishes between aldohexoses and ketohexoses, particularly effective for fructose.
Fructose & Sucrose Seliwanoff's Test: A positive reaction shows deep red, demonstrating fructose presence.

Molisch Test: Violet ring for carbohydrates, clear colorless for water, blue-black for starch, indicates presence of glucose and sucrose.
Iodine Test: Clear yellow with non-polysaccharides, blue-black for starch.
Benedict's Test: Clear blue solution for non-reducing sugars (sucrose, starch).
Barfoed's Test: Clear blue for polysaccharides, brick red for monosaccharides (glucose, fructose).
Seliwanoff's Test: Cherry-red when fructose is present, light yellow suggests water or negative results for non-sugars.